Classification

Phylum Arthropoda

Order Acari

Tick Biology and Life Cycles

Ticks (order Ixodida Leach, 1815) are blood-feeding ectoparasites of vertebrates representing important vectors of pathogens that cause diseases in humans and other animals (see Figure 1). They are obligate parasites at 1 or more developmental stages and may parasitize different classes of terrestrial vertebrates including mammals, birds, reptiles, and amphibians. All species of ticks have 4 stages in their life cycle, including the embryonated egg and 3 active stages: Larva, nymph (one or more instars), and adult (male and female). The tick life cycle may have many variations depending on the family and species. Depending on the number of hosts on which they feed, the tick may have a 1-host, 2-host, 3-host, or multi-host life cycle. During their off-host development phases, they can persist for long periods in the environment without feeding, particularly ticks in the family Argasidae (the soft ticks; see Sonenshine, 1991).

Figure 1. Life cycle of 3-host ixodid (hard) ticks. The adult is considered the diagnostic stage, as identification to the species level is best
achieved with adults. Most ticks of public health importance follow this pattern, including members of the genera Ixodes (Lyme borreliosis, babesiosis, human granulocytic ehrlichiosis), Amblyomma (tularemia, ehrlichiosis, and Rocky Mountain spotted fever), Dermacentor (Rocky Mountain spotted fever, Colorado tick fever, tularemia, tick paralysis), and Rhipicephalus (Rocky Mountain spotted fever, boutonneuse fever). — Three-host ixodid ticks have a life cycle that usually spans 3 years, although some species can complete the cycle in only 2 years. Adult females drop off the third host to lay eggs after feeding (1), usually in the fall. Eggs hatch into 6-legged larvae (2) and overwinter in the larval stage. In the spring, the larvae seek out and attach to the first host, usually a small rodent (3). Later in the summer, engorged larvae leave the first host (4) and molt into nymphs (5), usually in the fall. The ticks overwinter in this stage. During the following spring, the nymphs seek out and attach to the second host (6), usually another rodent or lagomorph. The nymphs feed on the second host and drop off later in the summer (7). Nymphs molt into adults (7a–7b) off the host in the late summer or fall and overwinter in this stage. The next spring, adults seek out and attach to a third host, which is usually a larger herbivore (including cervids and bovids), carnivore, or human (8). The adults feed and mate on the third host during the summer. Females drop off the host in the fall to continue the cycle. Females may reattach and feed multiple times. The 3 hosts do not necessarily have to be different species, or even different individuals. Also, humans may serve as first, second, or third hosts.
(Source: Division of Parasitic Diseases and Malaria, United States Centers for Disease Control and Prevention, 2017. Public domain.)

Ixodid ticks (family Ixodidae, the hard ticks) have a single nymphal instar and of them are non-nidicolous, meaning living in open and exposed habitats. In some species, only females result from the nymphal stage. These females reproduce parthenogenetically, that is, they do not need to mate to produce eggs (Sonenshine, 1991). Larvae and nymphs take a blood meal before molting to the next stage. Females lay several hundreds or thousands of eggs after engorging. Larvae, nymphs, and females may feed for several days, whereas males are usually intermittent feeders, taking small blood meals at each feeding and may remain on the host for long periods of time (Oliver, 1989; Sonenshine, 1991; 2013). Ixodid females have a single gonotrophic cycle. After completing feeding, they detach from the host to initiate oviposition (egg laying) in a secluded place, such as under vegetation, at the base of tree trunks, animal burrows, or even in cracks and crevices on the walls of human houses and animal sheds. Once oviposition is complete, the female dies. Males of the lineage Metastriata may stay on the hosts for long periods, mating with several females. These males usually mate on the host and need a blood meal to produce viable sperm. Males of the genus Ixodes (Prostriata lineage) typically mate off the host, which is typical of nidocolous tick species. Most ixodids have a 3-host life cycle, where each stage falls to the ground after feeding. Engorged larvae detach from a host to molt in the environment, the same occurring with resulting nymphs that seek another host to feed and detach as engorged nymphs to molt into males or females, which in turn will complete the parasitic life cycle onto another host (Oliver, 1989; Sonenshine, 1991).

Other species of ixodids have a 2-host tick life cycle, characterized by larvae that feed and molt on the same host, whereas the nymphs feed and detach after engorgement. Nymphs molt in the environment and the resulting males or females attach to another host to complete the parasitic life cycle. There are a few species, including some of economic importance, that have a 1-host life cycle. They molt on the host (from larva to nymph and then to adult) and detach from the host as engorged females (Oliver, 1989; Sonenshine, 1991).

Almost all argasid species (family Argasidae, the soft ticks) are nidicolous, meaning living in the protected habitat of a nest of a bird or mammal, and usually have more than 1 nymphal instar in their life cycle. Many species have a multi-host life cycle, although some do not, such as Ornithodoros lahorensis Neumann, 1908, which has a 2-host life cycle, and O. megnini that is a 1-host tick. In most argasid species, nymphs and adults are rapid feeders (generally taking around 30 to 40 minutes to complete a meal), but larvae usually remain feeding on a host for several days (Oliver, 1989; Sonenshine, 1991; 2013). Each immature stage feeds before molting to the next stage, but in some species of the genus Ornithodoros, such as O. brasiliensis Aragão, 1923, larvae molt to nymphs without feeding (Ramirez et al., 2016).

Some species of Argas and Ornithodoros may reproduce by autogeny (for example, A. persicus (Oken, 1818), O. lahorensis, O. tholozani (Laboulbène and Mégnin, 1882), O. tartakovskyi Olenev, 1931, and O. parkeri Cooley, 1936) (see Feldman-Muhsam, 1973; Oliver, 1989), and nymphs of some species (for example, O. fonsecai (Labruna and Venzal, 2009) and Nothoaspis amazoniensis) molt from the first to the second instar without feeding (Nava et al., 2010). Facultative autogeny may occur in the absence of a host. Females present multiple gonotrophic cycles and can feed many times, usually before mating and oviposition (Sonenshine, 1991), but for some species, the feeding behavior remains unknown.

Mating takes place off-host, and the female can lay a few hundred eggs after each meal, in each gonotrophic cycle. This is a survival mechanism, especially for nest dwelling species that depend on the presence, not always frequent, of their hosts. Exceptions may occur, for example, in adults of Antricola and Otobius that have vestigial mouthparts and a female may even lay eggs without feeding (this is called obligate autogeny) (Oliver, 1989; Sonenshine, 1991; 2013).

The biological life cycle involving multiple hosts is typical of argasids, which inhabit restricted environments and feed on the same individual host several times or in several hosts (of the same species or not) during their lifetime. Their habitat is intimately associated with that of their hosts. However, they can be found in remote locations far from human habitations such as loose soil, tree bark, animal burrows, caves, and in nests of wild and marine birds. Those that inhabit animal nests live in relatively stable microhabitats, feeding and reproducing continuously throughout the year. In this group, as in ixodids that inhabit nests, the development can be adapted seasonally, and a generation can take a year or more to develop in temperate climates (Oliver, 1989; Sonenshine, 1991; 2013).

The life cycle of the only species of family Nuttalliellidae is still unknown and the main hosts for each stage are uncertain. As an ixodid tick, Nuttalliella namaqua has a single nymphal instar and recently it has been shown that N. namaqua females may feed multiple times, like argasid females (Latif et al., 2012; Mans et al., 2012). Potential hosts already described for N. namaqua include mammals, reptiles, and birds (Mans et al., 2014). Larvae have been found parasitizing different species of rodents (Horak et al., 2012) and adults have been found in nests of birds (Keirans et al., 1976). Results of DNA analysis of the gut meals of females indicated that the ticks had fed on lizards of different species. Nymphs and adult females, therefore, have been shown to successfully feed on lizards in an experimental setting (Mans et al., 2011; 2014). Nymphs and adult females have been found in a variety of microhabitats in different regions of Africa (Mans et al., 2014). Although larvae may generally feed on rodents, the nymphal and adult stages seem to prefer reptiles, it is still premature to conclude that natural hosts of immature individuals or adults may feed exclusively on either mammals or reptiles. All these data may suggest a wider geographic distribution as well as host preference for N. namaqua.

Host Range

Ticks have variable degrees of specificity for their hosts, with some species parasitizing very different groups of animals. Some species of ticks only feed on a narrow range of host groups or on a specific host species (host-specific = narrow host range), whereas others are less selective (generalists), using a wide range (broad host range) of vertebrates as hosts (Sonenshine, 2013). Mammals serve as hosts for more tick species than birds, reptiles, and amphibians. Among mammals, rodents are one of the most common host groups, particularly for immature stages of hard ticks.

In general, immature stages of species that have a 2- or 3-host life cycle feed on small animals (for example, rodents), whereas adults prefer medium- and large-sized animals. In ticks that use more than 1 host, as happens with most species of the genus Amblyomma, immature stages are less specific than the adults, and may parasitize a greater diversity of hosts (Sonenshine, 2013). Host specificity is influenced by several factors, including host defense mechanisms against tick infestations, such as physical barriers in the body, self-cleaning behavior, and immunological responses.

Both passive and active questing methods are used by ticks to find their hosts. Passive species, such as most nidicolous ticks, remain in their habitat (for example, grassy fields, brushy areas, animal burrows, nests) and depend upon contact with vertebrate animals that invade their space incidentally. Most non-nidicolous ticks are hunters; they use ambush behavior (called questing), referring to ticks living in grass or brush-covered habitats typically climbing to the tips of stems or branches of vegetation where they wait for passing hosts to brush against them (Sonenshine, 2013). The success of a tick in finding a host depends on several factors, including the height of the vegetation on which ticks of different stages are waiting for a host, as well as the response of ticks to specific stimuli, such as body odor, body heat, and carbon dioxide (CO₂), which are emitted from the host. Also, the type of environment has a direct influence on the qualitative and quantitative availability of hosts for the ticks.

The seasonal variation in the biological cycles and development of a species of tick is determined by the host and by abiotic factors, such as temperature, photoperiod, and relative humidity. Temperature plays an important role in determining the duration of each off-host development phase such as: For example, oviposition, egg incubation, larvae hatching, and ecdysis (molting from one stage to another). The photoperiod has a direct influence in the induction of diapause, mainly in nonequatorial regions, modulating the cycles in seasonal rhythms that assure the ticks the synchronization of their activities with the appropriate climatic conditions (Oliver, 1989; Sonenshine, 2013).

Two types of diapause are known: Behavioral (suppression of host-seeking activity or delay of engorgement) and morphogenetic or developmental (delay during embryogenesis) in the ecdysis of immature stages or in the oviposition of females (Sonenshine, 2013). This is an important strategy in the biology of both nidicolous and non-nidicolous ticks, such as Amblyomma sculptum, that use both larval and behavioral diapause (Labruna et al., 2002; 2003).

Taxonomic History

Millions of years ago, during the Paleozoic Era, ticks diverged from other Acari Leach, 1817, probably as parasites of the ancestors of modern vertebrates such as reptiles and amphibians (Dantas-Torres, 2018). Therefore, ticks disappeared when their conquering continental hosts went extinct. Fossil evidence indicates that modern tick lineages originated and diverged during the Mesozoic Era (Mans et al., 2016). There are 2 fossil species in the family Argasidae Koch, 1844 (soft ticks), both of which are in the genus Ornithodoros Koch, 1844, namely, O. antiquus Poinar, 1995 and O. jerseyi (Klompen and Grimaldi, 2001). The third argasid fossil with an adequate morphological description corresponds to a male of Ornithodoros sp. found in Dominican amber from about 25 Ma (= million years ago) (Estrada-Peña and De La Fuente, 2018). These authors suggested that many of the lineage splits were produced when the landmasses were still forming the supercontinent Pangea, or Laurasia and Gondwanaland. Fossil species in the family Ixodidae Koch, 1844 (hard ticks) include Amblyomma birmitum Chitimia-Dobler et al., 2017, Cornupalpatum burmanicum Poinar and Brown, 2003, Compluriscutula vetulum Poinar and Buckley, 2008, Ixodes succineus Weidner, 1964, and Haemaphysalis cretacea Chitimia-Dobler et al., 2018. The only fossil of the genus Haemaphysalis Koch, 1844 may actually belong to another genus (Guglielmone et al., 2016; see also Dantas-Torres, 2018). Recently, a fossil species, namely Deinocroton draculi Peñalver et al., 2017, was described in a recently proposed fossil family Deinocrotonidae Peñalver et al., 2017. This species resembles Nuttalliella namaqua Bedford, 1931, which represents a basal lineage within the order Ixodida.

Current Taxonomic Position of Tick Genera

As of 2019, the Ixodida was represented by 956 species (948 extant and 8 fossil species) (see the supplementary material for more about this), which are considered to be distributed into 4 families: Argasidae (215 species), Ixodidae (733 species), Nuttalliellidae Bedford, 1931 (monospecific), and Deinocrotonidae (monospecific) (Dantas-Torres, 2018; Du et al., 2018; Kwak, 2018; Barker, 2019; Tomlinson and Apanaskevich, 2019).

Excluding the monospecific families, the genus-level classification of ticks has been a long issue of debate and changes are constantly proposed, particularly in the family Argasidae. Following are detailed descriptions of some groups of ticks.

Family Argasidae: The Soft Ticks

The family Argasidae, or the soft ticks, includes 215 extant and 2 fossil species (Dantas-Torres, 2018), many of which have not been yet adequately described. Estrada-Peña and colleagues (2010) suggest that there is still a long way to go to achieve an accurate view of the main evolutionary lines of the family. The soft ticks are so-named because they have no hard plate on their back (called the scutum in hard ticks; see below). They also commented that there is no consensus about the relevant morphological features for the determination of argasid species nor there is consensus on the appropriate genus for many species. According to Venzal and colleagues (2008), only larval morphological features have been adequately defined for a specific determination, mainly in the absence of DNA sequence data.

In this chapter, the genus-level classification adopted by the last lists of ticks of the world is used (Guglielmone et al., 2010; Dantas-Torres, 2018). Also included are 2 recent genera proposed by Barker and Burger (2018) and new species described in 2019 (Barker, 2019; Martins et al., 2019; Tomlinson and Apanaskevich, 2019; Sun et al., 2019). However, the genus-level classification of argasids is still controversial, with some subgenera perhaps deserving to be elevated to the rank of genera (Burger et al., 2014; Mans et al., 2019). Based on 4 classification schemes for the argasid genera (the Soviet, American, French, and Cladistic schools), the subfamily Argasinae (Trouessart, 1892, pro parte) Pospelova-Shtrom, 1946 (ectoparasites of chickens and wild birds) is well supported by molecular data (Burger et al., 2014). However, this is not true for the subfamily Ornithodorinae Pospelova-Shtrom, 1946. After sequencing the mitochondrial genomes of 12 species, Burger and colleagues (2014) concluded that there is a clade of Neotropical species within the Ornithodorinae that includes the genera Antricola Cooley and Kohls, 1942 and Nothoaspis Keirans and Clifford, 1975, and the subgenera Alectorobius Pocock, 1907, Parantricola Cerny, 1966, and Subparmatus Clifford et al., 1964. On the other hand, the genera and subgenera of the Neotropical Ornithodorinae clade were placed in the genus Carios Latreille, 1796, as previously proposed by Klompen and Oliver (1993). Probably, the generic classification of argasids adopted here (Guglielmone et al., 2010) will change in the future, considering that new genomic data are becoming available, shedding new light onto this issue. For instance, Mans and colleagues (2019) generated a total of 83 whole mitochondrial genomes, 18S rRNA and 28S rRNA genes and proposed a revised genus-level classification for the family Argasidae. The new classification corresponds broadly with the morphological cladistic analysis of Klompen and Oliver (1993), however, with the erection of different subgenera to the genus level.

The genus Antricola is represented by 17 species distributed in the Neotropical region, most of them being restricted to Cuba. Besides Cuba, some species have been described from Mexico, Puerto Rico, Brazil, and Venezuela (Jones et al., 1972; De La Cruz, 1973; 1976; 1978; De La Cruz and Estrada-Peña, 1995; Camicas et al., 1998; Estrada-Peña et al., 2004; Guglielmone et al., 2010). The main contributions to the taxonomy of this genus were produced by De La Cruz during the 1970s (De La Cruz, 1973; 1976; 1978). The number of species described from 1910 to 2004 is shown in Figure 2A. A key for the currently known species of Antricola is available in Estrada-Peña and colleagues (2004).

The genus Argas Latreille, 1795 is currently represented by 62 species, distributed in the Afrotropical, Australasian, Neotropical, and Oriental regions (Camicas et al., 1998). The number of species described from 1795 to 2012 is shown in Figure 2B. Most of the species have been described in the last century, and half of them from 1960 to 1980 (35 species). The main contributions were those of Kohls and Hoogstraal (1961), Kohls and colleagues (1970), and Keirans and colleagues (1979). According to Muñoz-Leal (2018), the morphology of nymphs and adults of Argas are less informative taxonomically, but some integumental dorsal features may be useful for a specific identification.

The genus Nothoaspis is composed of 3 species (N. reddelli Keirans and Clifford, 1975 in Mexico; N. amazoniensis Nava et al., 2010 in Brazil; and N. setosus (Kohls et al., 1969) n. comb. (Muñoz-Leal et al., 2019). The last species was previously assigned to the genus Ornithodoros, but the morphological and molecular analysis of O. setosus larvae recently collected of the local type of this species showed that it belongs to the genus Nothoaspis. This genus is restricted to the Neotropical region (Keirans and Clifford, 1975; Nava et al., 2010; Muñoz-Leal et al., 2019). Note that N. setosus is referred to as O. setosus in the supplementary list for this chapter.

The genus Ornithodoros is the most speciose in the family Argasidae and comprises 131 extant and 2 fossil species (note that the fossil species are not included in the supplementary list for this chapter). They are distributed in the Afrotropical, Australasian, Oriental, Nearctic, Neotropical, and Palearctic regions (Camicas et al., 1998). The number of species described from 1820 to 2019 is shown in Figure 2C. As for Argas, most of them were described from 1960–1969 (29 species), and the main contributions are those of Clifford and colleagues (1964), Kohls and Clifford (1964), Kohls and colleagues (1965; 1969a), followed by those described from 2010–2019 (20 species) (Dantas-Torres et al., 2012a; Trape et al., 2013; Venzal et al., 2012; 2013; 2015; Barros-Battesti et al., 2015; Labruna et al., 2016; Muñoz-Leal et al, 2016; 2017; Bakkes et al., 2018; Sun et al., 2019).

Figure 2. Argasidae genera. A) Number of Antricola species chronologically described from 1910 to 2004; B) number of Argas species chronologically described from 1795 to 2012; C) number of Ornithodoros species chronologically described from 1820 to 2019.
(Source: D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres. License: CC BY.)

The nymphs and adults of Ornithodoros are very similar and no reliable keys are currently available for their identification. On the other hand, larvae can be reliably separated by chaetotaxy of dorsum and venter, morphology of hypostome and, if present, dorsal plate.

The genus Otobius (Banks, 1912) includes 2 species, namely O. megnini (Dugès, 1883) and O. lagophilus Cooley and Kohls, 1940. The species O. megnini is thought to have had its original center of distribution in the arid lands of southwestern North America (Keirans and Pound, 2003). It was probably introduced into Central America and South America on both cattle and horses, and it was imported into South Africa in the ears of horses from South America or, perhaps, Mexico (Keirans and Pound, 2003). Currently, it is distributed worldwide, occurring in Afrotropical, Nearctic, Neotropical and Oriental regions (Camicas et al., 1998; Flores and Solís, 2018; Hosseini-Chegeni et al., 2018). The species O. lagophilus is restricted to the Nearctic region, parasitizing wild rabbits, occurring in Canada and the United States (Herrin and Beck, 1965).

A life cycle diagram for the argasid ticks is shown in Figure 3.

Figure 3. Multihost life cycle for argasid (soft) ticks. Unlike the Ixodidae, members of the family Argasidae have 2 or more nymphal stages, each of which requires a blood meal. This pattern is referred to as the multihost life cycle. Two species of public health concern in the United States, Ornithodoros hermsi and O. turicata, are vectors of tick-borne relapsing fever (TBRF) spirochetes. In Africa and Asia, O. moubata is a vector of TBRF spirochetes. Members of the genus Carios are vectors of TBRF spirochetes in Central America and South America. — Mating usually occurs, and egg-laying always occurs, off the host in a sheltered area (usually an animal nest). Eggs hatch into 6-legged larvae (1) in the parents’ sheltered area. They quest for a host in the vicinity of the sheltered area. Once a suitable host is found, they feed for anywhere from 1 hour to several days, depending on the species (2). After feeding, the larvae leave the host and molt into the first nymphal instars in the sheltered area (3a–3b). The nymphs quest for, and feed on, the second host (4) rapidly (usually about an hour). The second host is usually the same species, and often the same individual, as the first host. The first nymphal instars leave the host and molt into the next nymphal instars in the sheltered area (5a–5b). This cycle can continue to accommodate up to 7 nymphal instars (6), depending on the species. After the last nymphal instar has fed, it leaves the host and molts into an adult (7a–7b) in the sheltered area. Adults may continue to feed on the host (8), feeding rapidly and detaching after each blood meal. Females of some species lay egg batches after each meal. Humans are usually only incidental hosts for argasid ticks and may be fed upon by any of the stages.
(Source: United States Centers for Disease Control and Prevention, Division of Parasitic Diseases and Malaria, 2017. Public domain.)

Family Ixodidae: The Hard Ticks

The family Ixodidae currently comprises 733 extant and 5 fossil species. This family is divided into 2 lineages (that is, Prostriata and Metastriata) found in all zoogeographic regions of the world (Guglielmone et al., 2014). The ixodids are called hard ticks because they have a big plate on their back called the scutum. The Prostriata (anal groove curves anterior to anus) contains only 1 genus, whereas the Metastriata (when present, anal groove curves posterior to anus) contains 14 genera (Burger et al., 2012; Barker and Burger, 2018). In contrast to what occurs with the family Argasidae, the genus-level classification of Ixodidae is more stable and consensual (Barker and Murrell, 2002; Guglielmone et al., 2014; Dantas-Torres, 2018). Nonetheless, some systematic issues (for example, paraphyly of the genus Amblyomma Koch, 1844) are still under debate (Barker and Burger, 2018), but the 2 genera proposed by these authors are here included with the new combinations.

The genus Ixodes Latreille, 1795 comprises 255 extant species and 1 fossil species. They are distributed in the Afrotropical, Australasian, Nearctic, Neotropical, Oriental, and Palearctic regions, and combinations of these regions including remote islands, and the polar area (circumpolar) (Guglielmone et al., 2014; Estrada-Peña et al., 2014; Hornok et al., 2014, 2016; Ash et al., 2017; Apanaskevich and Bermúdez, 2017; Guo et al., 2017; Heath and Palma, 2017; Kwak et al., 2018; Barker, 2019). This is the largest tick genus, and most of the species originated on Gondwanaland (the southern continental landmass that began to break up in the early Jurassic around 184 million years BCE) (Guglielmone et al., 2014). The number of species described from 1758 to 2019 is shown in Figure 4A. The highest number of species were described during the 1950s and 1960s, with 47 and 39 species, respectively, mainly due to the contributions of Arthur (1956; 1960a), Kohls (1953; 1956a; 1956b; 1957; 1969), Kohls and Clifford (1962; 1966; 1967), and Kohls and colleagues (1969b).

The genus Archaeocroton Barker and Burger, 2018 was proposed for Amblyomma sphenodonti (Dumbleton, 1943), the tuatara tick of New Zealand. This new combination was mainly because this species in Amblyomma leaves this genus polyphyletic, and indeed, taxonomically unstable (Barker and Burger, 2018). The species was named Archaeocroton sphenodonti (Dumbleton, 1943).

The genus Amblyomma is 1 of the largest genera and comprises 137 extant and 1 fossil species, distributed in the Afrotropical, Australasian, Nearctic, Neotropical, and Oriental regions. Some species are found in more than 1 region, presenting Afrotropical–Neotropical, Afrotropical–Oriental, Afrotropical–Palearctic, Australasian–Oriental, Nearctic–Neotropical, Oriental-Palearctic, Afrotropical–Australasian–Oriental, or Australasian–Oriental–Palearctic distributions (Guglielmone et al., 2014; Nava et al., 2014a; 2014b; Krawczak et al., 2015; Apaneskevich and Apaneskevich, 2018). Chitimia-Dobler et al. (2017) commented that the genus Amblyomma was split in Gondwanaland, with a concurrent spread into what are now known as Africa, Australia, Asia, and South America. No species occurs exclusively in the Palearctic region (Guglielmone et al., 2014). The Neotropical region is home to the largest number of species within this genus, followed by the Afrotropical region. The number of species described from 1758–2019 is shown in Figure 4B. The highest number of species was described from 1840–1849 and 1890–1899, with 25 taxa each of those decades. The greatest contributions were those of Koch (1844) and Neumann (1899), who described 20 and 21 species of Amblyomma, respectively, during those years. In the first 10 years of the last century, Neumann (1901; 1904; 1905; 1906; 1907; 1911) described 16 species belonging to this genus.

The genus Anomalohimalaya Hoogstraal et al., 1970 is represented by 3 species, namely A. lamai Hoogstraal et al., 1970 from Nepal, A. lotozkyi Filippova and Panova, 1978 from Tajikistan, and A. cricetuli Teng and Huang, 1981 from China. They are exclusive to the Palearctic region and found in lands that once constituted Laurasia (Hoogstraal et al., 1970; Filippova and Panova, 1978; Filippova and Bardzimashvily, 1992; Guglielmone et al., 2014).

The genus Bothriocroton Keirans, King and Sharrad, 1994 includes 7 species: B. undatum (Fabricius, 1775), B. hydrosauri (Denny, 1843), B. concolor (Neumann, 1899), B. oudemansi (Neumann, 1910), B. auruginans (Schulze, 1936), B. tachyglossi (Roberts, 1953), and B. glebopalma (Keirans, King and Sharrad, 1994). They are found exclusively in the Australasian region (Klompen et al., 2002; Beati et al., 2008; Burger et al., 2012; Barker and Walker, 2014).

The monospecific genus Cosmiomma Schulze, 1919 is found in the Afrotropical region and it is represented only by C. hippopotamensis (Denny, 1843) (Arthur, 1960b).

The genus Dermacentor Koch, 1844 is represented by 40 species, which are of Afrotropical, Nearctic, Neotropical, Oriental, Palearctic, Australasian–Oriental, Nearctic–Neotropical, and Nearctic–Palearctic distribution (Guglielmone et al., 2014; Rubel et al., 2016; Vongphayloth et al., 2018). According to Nava and colleagues (2017), the species are more prevalent in lands of Laurasian origin than in Gondwanan lands. The number of species described from 1776–2016 is shown in Figure 4C. Most species were described during the 1930s, with 10 taxa described during that decade. The main contributions to this genus were those of Schulze (1933; 1935; 1937; 1939). In the last 5 years, 1 species was described in Central America (Apanaskevich and Bermúdez, 2013a) and 4 taxa were described to in the Oriental region (Apanaskevich and Apanaskevich, 2015a; 2015b; 2015c; 2016).

Figure 4. Ixodidae genera. A) Number of Ixodes species chronologically described from 1758 to 2019; B) number of Amblyomma species chronologically described from 1758 to 2019; C) number of Dermacentor species chronologically described from 1776 to 2016.
(Source: D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres. License: CC BY.)

The genus Haemaphysalis comprises 169 extant species and 1 fossil species, distributed in the Afrotropical, Australasian, Nearctic, Neotropical, Oriental, and Palearctic regions, and combinations of these regions: Afrotropical–Neotropical, Afrotropical–Palearctic, Australasian–Oriental, Nearctic–Neotropical, Oriental–Palearctic, Afrotropical–Oriental–Palearctic, and Australasian–Oriental–Palearctic (Guglielmone et al., 2014). This genus is poorly represented in the Nearctic and Neotropical regions, with the majority of species occurring exclusively in the Oriental region. The inclusion of the fossil species H. cretacea in this genus (Chitimia-Dobler et al., 2018) has been questioned (Dantas-Torres, 2018). The number of species described from 1826–2019 is shown in Figure 5A. The greatest numbers of species were described during the 1960s with 31 taxa, followed by the 1970s with 22 species. The greatest contributions were those of Hoogstraal and colleagues (1965; 1969), Hoogstraal and Trapido (1966), and Hoogstraal and Kim (1985). In the last decade, 6 species were described (Tomlinson and Apanaskevich, 2019).

The genus Hyalomma Koch, 1844 is represented by 27 species, distributed in the Afrotropical, Oriental, Palearctic, Afrotropical-Palearctic, Oriental–Palearctic, and Afrotropical–Oriental–Palearctic regions (Guglielmone et al., 2014). The greatest number of species is found in the Afrotropical, followed by the Palearctic regions. According to these authors, the genus is absent in the Australasian, Nearctic, and Neotropical regions. The highest numbers of species were described during the 1840s with 8 taxa described, and the main contributions were those of Koch (1844) who described 7 species during that decade. The number of species described from 1758–1982 is shown in Figure 5B.

The genus Margaropus Karsch, 1879 is represented by 3 species, namely M. reidi Hoogstraal, 1956, M. wileyi Walker and Laurence, 1973, and M. winthemi Karsch, 1879, which occur only in the Afrotropical region (Arthur, 1960b; Walker and Laurence, 1973; Guglielmone et al., 2014).

The genus Nosomma Schulze, 1919 is represented only by 2 species, namely N. monstrosum (Nuttall and Warburton, 1908) and N. keralensis Prakasan and Ramani, 2007. Both species are exclusively from the Oriental region (Guglielmone et al., 2014).

The genus Rhipicentor Nuttall and Warburton, 1908 is represented by 2 species, namely R. bicornis Nuttall and Warburton, 1908 and R. nuttalli Cooper and Robinson, 1908, both of which are exclusively found in the Afrotropical region (Guglielmone et al., 2014).

The genus Rhipicephalus Koch, 1844 includes 85 species. According to Guglielmone and colleagues (2014), 63 species are exclusively found in the Afrotropical region, 7 species occur exclusively in the Palearctic region, and 3 are found only in the Oriental region. The remaining species are distributed in the Australasian, Nearctic, and Neotropical regions, but they are not exclusively from these regions. The number of species described from 1806–2013 is shown in Figure 5C. The highest numbers of species described were from 1900–1910 with 18 taxa, followed by the 1910s with 12 species. The greatest contributions were those of Neumann (1899; 1901; 1904; 1905; 1906; 1907; 1911; 1913). The 2 latest species described in this genus were in 2013 (Apanaskevich et al., 2013b; Horak et al., 2013).

Figure 5. Ixodidae genera. A) Number of Haemaphysalis species chronologically described from 1826 to 2019; B) number of Hyalomma species chronologically described from 1758 to 1982; C) number of Rhipicephalus species chronologically described from 1806 to 2013.(Source: D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres. License: CC BY.)

The genus Robertsicus Barker and Burger, 2018 was proposed for Amblyomma elaphensis (Price, 1959), from the Chihuahuan Desert of Mexico and the southeastern United States. This new combination was meant to solve for the polyphyly of the genus Amblyomma that is in the same situation (Barker and Burger, 2018). These authors named the species Robertsicus elaphensis (Price, 1959).

Family Nuttalliellidae

Nuttalliellidae is a monospecific family, which presently is restricted to the Afrotropical region (Bedford, 1931; Keirans et al., 1976; Camicas et al., 1998; Mans et al., 2011; 2016). Based on analysis of mitochondrial genome and nuclear ribosomal RNA (18S and 28S) sequence data, Mans and colleagues (2011; 2019) suggested that the Nuttalliellidae is basal to other tick families, representing the closest extant lineage to the last common ancestral tick lineage. According to these authors, nuttalliellids almost became extinct during the great end-Permian mass extinction event, leaving Nuttalliellia namaqua as the closest living relative to the ancestral tick lineage.

Family Deinocrotonidae (Fossil)

Deinocrotonidae is a fossil tick family recently described based on fossil material retrieved in 99-million-year-old Cretaceous amber from Myanmar (Peñalver et al., 2017). Deinocroton draculi was found in association with Cornupalpatum burmanicum, suggesting that both deinocrotonids and ixodids fed on blood from feathered dinosaurs (Peñalver et al., 2017). Morphologically, deinocrotonids resemble nuttalliellids, but no DNA sequences from the former are available to assess their phylogenetic relationship.

Descriptions of Selected Tick Genera

In this section, morphological descriptions are presented for the identification of several tick genera as used in scientific papers. The fossil family Deinocrotonidae and the fossil genera Deinocroton, Cornupalpatum, and Compluriscutula are not included.

Argasid Tick Genera

Genus Argas

The following morphological descriptions are based on Cooley and Kohls (1944) and Kohls and colleagues (1970).

Larva: Dorsal surface with around 25–30 pairs of setae, dorsal plate oval and elongated; ventral surface with less than 7 pairs of setae and 1 pair on valves; posteromedial seta present or absent; 2 pairs of short post-hypostomal setae; hypostome rounded at apex, dentition 2/2 at basis to 3/3 at apex (Figure 6). Nymph: Outline oval, discs present, distributed more or less symmetrically dorsally; idiosoma mammillated, flattened dorsoventrally, with suture and lateral margin demarcating the dorsal and ventral surfaces; Haller’s organ with transversely slit-like aperture, placed slightly laterally (Figure 7). Adult: Idiosoma flattened, dorsal and ventral surface equal, margin distinct flattened, made up a radial striae or quadrangular plates; sutural line present; flattened margin not obliterated even when tick is fully fed; capitulum ventral; integument leathery, minutely wrinkled in folds, of many shapes often intermingled with small, rounded, buttons each with a pit on top and often bearing a hair in the pit; discs present on both dorsal and ventral surfaces and placed in more or less radial lines; eyes absent (Figure 8).

Figure 6. Larvae of Argasidae genera. A) Otobius megnini, dorsal view; B) Argas miniatus, dorsal view; C) Ornithodoros brasiliensis, dorsal view; D) Or. fonsecai, dorsal view. Scale bars: A–C = 100 μm; D = 120 μm.
(Source: D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres. License: CC BY-NC-SA 4.0.)

Figure 7. Nymphs of Argasidae genera. A, B) Argas miniatus, dorsal and ventral view, C) Otobius megnini, ventral view; D) Antricola guglielmonei, dorsal view; E) Ornithodoros brasiliensis dorsal view. Scale bars: A, B, E = 1,000 μm; C = 300 μm; D = 200 μm.
(Source: D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres. License: CC BY-NC-SA 4.0.)

Figure 8. Adults of Argasidae genera. A) Argas miniatus female, ventral view; B, C) Antricola guglielmonei, spiracular plate and dorsal view; D) Ornithodoros sp., dorsal view. Scale bars: A, D = 1,000 μm; B = 100 μm; C = 200 μm.
(Source: D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres. License: CC BY-NC-SA 4.0.)

Genus Antricola

The following morphological descriptions are based on Cooley and Kohls (1944), Estrada-Peña and colleagues (2004), and Barros-Battesti and colleagues (2013).

Larva: Dorsal surface with 14 pairs of setae, typically 14 (11 dorsolateral, 3 central dorsal); dorsal plate, large and elongated with lateral margins parallel, narrowing anteriorly; eyes absent; ventral surface with 11 pairs of setae (3 sternal setae, 3 post-coxal setae, 4 circumanal + 1 on valves), and 1 posteromedial seta; 2 pairs of long post hypostomal setae, hypostome pointed, dentition 3/3 in anterior three-fourths, then 2/2 posteriorly to basis; palps with 18 setae, number of setae on palpal article 1–4, respectively 0, 4, 5 and 9; pulvilli large, claws absent (except in A. marginatus); dorsal hump absent; Haller’s organ with a rounded capsule, open only in a small central portion. Nymph: Body outline suboval, pointed anteriorly, covered by tubercles, most of them bearing short setae, some single, others in groups; hypostome short, broad and rounded apically, with small denticles on anterior and lateral margins; cheeks absent; spiracular plates oval, relatively large, expanded and dorsally visible in some specimens, with numerous minute pores. Adult: Dorsal surface flattened and marginated; cuticle semi-translucent and smooth, shining, and with tubercles and tufts of setae; dorsomarginal grooves well defined; transverse post-anal groove present. Basis capituli slightly longer than wide, rounded laterally, hypostome small, slightly longer than wide, scoop-like, without denticles.

Genus Ornithodoros

The following morphological descriptions are based on Venzal and colleagues (2006) and Barros-Battesti and colleagues (2013).

Larva: Dorsal surface of idiosoma usually with 13–14 pairs of setae (with some exceptions); dorsal plate absent in few species, but present in the majority, varying in shape, from triangular to pyriform (bat-associated group) to elongated subrectangular with anterior extremity narrowed; venter with 7–8 pairs + 1 pair on anal valves, and 1 posteromedial seta (which may be absent). Basis capituli with lateral angles slightly rounded, lateral auriculae present or absent, hypostome with apex rounded or pointed, dental formula: 5/5 to 2/2 at apex, 4/4 to 2/2 in medial portion and 2/2 at basis; Haller’s organ with capsule aperture transversely slitlike, large, occupying all of the dorsum with many small setae, or small occupying part of the dorsum. Nymph: Body outline oval, slightly pointed anteriorly, idiosoma covered by tile-like mammillae; presence of 4 pairs of bulging lateral structures resembling large mammillae on supracoxal folds between legs I–IV (soil-living group) or absent (bat-associated group), hypostome rounded on apex; humps present (only in the soil-living group) or absent (bat-associated group), Haller’s organ similar to the larvae. Adult: Idiosoma suboval, with rounded margins, without marginal lateral sutures; well-developed hypostome with well-defined rows of denticles; hood present; sometimes cheeks present; eyes, when present are arranged anterolaterally to the supracoxal folds; integument leathery, with tiny mammillated elevations, interspersed by discs on both the dorsal and ventral surfaces.

Genus Otobius

The following morphological descriptions are based on Cooley and Kohls (1940; 1944), Guglielmone and colleagues (2006), and Barros-Battesti and colleagues. (2013).

Larva: Integument striated, dorsal surface with 7–10 pairs of setae, dorsal plate large, elongate tapering slightly posteriorly; 2 pairs of eyes; ventral surface with 5 pairs of setae + 1 pair on valves; pulvilli present on all tarsi, not enlarged, claws present, Haller’s organ with capsule aperture large and rounded, with posterior projections; hypostome long without corona, dental formula 2/2. Nymph: Camerostome and hood absent; hypostomal dentition 4/4; idiosoma panduriform, integument striated and spinous; spiracular plate cone-shaped; Haller’s organ with capsule aperture transversely slit-like, elevated and large, bordered with prolonged pointed projections and with small setae internally. Adult: Integument granulated and with no change of pattern at the sides; small discs present; hood and eyes absent; hypostome vestigial, not functional to the hematophagy. The morphology is very similar between the 2 species, but the distance between the dorsal small discs in Otobius megnini is larger than in O. lagophilus.

Genus Nothoaspis

The following morphological descriptions are based on Nava and colleagues (2010) and Barros-Battesti and colleagues (2013) and Muñoz-Leal and colleagues (2019).

Larva: Dorsal plate with isosceles triangle shape occupying entire length of the dorsum of unfed specimens with a curvy-notched posterior margin; lateral margins of basis capitulum provided with a small bulge dorsal; surface with 12–13 pairs of setae; hypostome with apex pointed, dental formula 2/2 with 20 denticles in each row, corona absent. Nymph: Idiosoma twice as longer as wide, anteriorly more abruptly narrowing than posteriorly; false shield covered by cells (irregular in shape and size) occupying the anterocentral area of dorsum, most of them at least with 1 seta; setae short, except for posterior margin of idiosoma, where setae are larger. Ventral surface with integument also covered by cells (irregular in shape and size), except for a narrow area located between coxae I and III; spiracular plate small; basis capituli subrectangular in outline, with 1 pair of post-hypostomal setae and at least 7 pairs of sublateral setae, bordered posteriorly by integumental fold; postpalpal setae absent; hood large, broadly rounded, not entirely covering capitulum, cheliceral blades, palpal articles II–IV visible dorsally; ventrally, article I forms elongate flaps protecting the pointed hypostome, dental formula 4/4 apically, 5/5 at base. Adult: Presence of false shield or nothoaspis (pseudoscutum), an anteriorly projecting hood covering the capitulum, a medial extension of palpal article I (flaps), genital plate extending from coxa I to IV, absence of 2 setae on the internal margin of the flaps, a small hypostome without denticles, presence of a central pore in the base of hypostome, and a reticulate surface pattern on the posterior half of the nothoaspis in males.

Ixodid Tick Genera

Genus Ixodes

The following morphological descriptions are based on Coley and Kohls (1945), Clifford and Anastos (1960), Clifford and colleagues. (1973), Nava and colleagues (2017), Apaneskevich and Lemon (2018), and Kwuat and colleagues (2018).

Larva: Anal groove anterior to anus; sensilla sagittiformia absent; with 2 pairs of post-hypostomal setae; eyes and festoons absent; 6 legs (Figure 9). Nymph: Anal groove anterior to anus; eyes and festoons absent; genital pore absent; spiracular plates circular ; 8 legs; nymphs are smaller than adults (Figure 10). Adult: An anal groove is present anterior to the anus, forming an arch; eyes and festoons are absent; an inornate scutum is present; spiracular plates are semicircular or oval; and there is a spur on the coxae. Sexual dimorphism is pronounced. The male venter is largely covered by 7 sclerotized plates. Males have ventral plates. Females have porose areas. The denticles of the female hypostome are well developed, while those of the male are usually few and small, often appearing only as mild crenulations (Figures 11–12).

Figure 9. Larvae of Ixodidae genera. A) Ixodes auritulus group, ventral view; B) Amblyomma romitii, dorsal view; C) Dermacentor nitens, gnathosoma dorsal view; D) Haemaphysalis juxtakochi, ventral view; E) Rhipicephalus microplus, gnatosoma dorsal view; F) Rhipicephalus sanguineus, ventral view. Scale bars: A = 250 μm; B, F = 30 μm; C = 40 μm; D = 60 μm; E = 20 μm.
(Source: D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres. License: CC BY-NC-SA 4.0.)

Figure 10. Nymphs of Ixodidae genera. A) Ixodes luciae anal groove, ventral view; B) Haemaphysalis juxtakochi gnathosoma, dorsal view; C) Amblyomma longirostre, dorsal view; D) Dermacentor nitens gnathosoma, dorsal view; d1) Dermacentor nitens spiracular plate; E) Rhipicephalus sanguineus s. l. anal groove, ventral view; F) Rhipicephalus sanguineus s. l. gnathosoma, ventral view; G) Rhipicephalus microplus gnathosoma, ventral view. Scale bars: A, E = 100 μm; B, G = 20 μm; C = 300 μm; D = 80 μm; d1 = 40 μm.
(Source: D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres. License: CC BY-NC-SA 4.0.)

Figure 11. Adults of Ixodidae genera. A) Ixodes aragaoi female, ventral view; B) Bothriocroton sp. male, dorsal view; C) Amblyomma (Aponomma) quadricavum female, ventral view; D) Haemaphysalis juxtakochi male, ventral view; E) H. leporipalustris, gnatosoma ventral view; F) Anomalohimalaya female, dorsal and ventral view. Scale bars: A = 500 μm; C = 1,000 μm; D = 300 μm; E = 100 μm.
(Sources: A, C–E) D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres; B) adapted from Baker and Walker, 2004; F) adapted from Hoogstraal et al., 1970. License: CC BY-NC-SA 4.0.)

Figure 12. Adults of Ixodidae genera. A) Nosomma sp. male, ventral view; B) Hyalomma female, dorsal view; C) Amblyomma sculptum male, dorsal view; D) Rhipicephalus (Boophilus) microplus male, ventral view; E) Dermacentor sp. male, gnathosoma dorsal view; F) Rhipicephalus sanguineus s. l. male, dorsal view; G) Rhipicentor sp. male, ventral view. Scale bars: C = 250 μm; D = 500 μm; E = 250 μm.
(Sources: A) Adapted from Prakasan and Ramani, 2007; B) adapted from Walker et al., 2003; C–F) D. Moraes Barros-Battesti, V. Castilho Onofrio, and F. Dantas-Torres; G) adapted from Nuttall and Warburton, 1908. License: CC BY-NC-SA 4.0.)

Genus Dermacentor

The following morphological descriptions are based on Arthur (1960b), Yunker and colleagues (1986), Apanaskevich and Bermúdez (2013a), and Barker and Walker (2014).

Larva: Sensilla sagittiformia present; eyes present; a pair of posthypostomal setae; anal groove absent; 3 marginal dorsal setae anterior to the sensilla sagittiformia on dorsal surface; idiosoma with 9 festoons. Nymph: Eyes present; anal groove absent; spiracular plate circular to suboval with few and large goblet cells. Adult: Scutum in females usually ornate (inornate in Dermacentor nitens Neumann, 1897); anal groove contouring the anus behind; spiracular plates subcircular to comma-shaped (subcircular in D. nitens with large goblet cells); basis capituli more broad than long, rectangular dorsally; eyes on the scutum usually present and distinct. Male: Scutum usually ornate (inornate in D. nitens); anal groove posterior to the anus; coxae I–IV increase progressively in size; dorsal and posterior margins with festoons.

Genus Amblyomma

The following morphological descriptions are based on Klompen and colleagues (1996), Barbieri and colleagues (2007), and Nava and colleagues (2017).

Larva: Anal groove absent, sometimes indistinct; sensilla sagittiformia present on idiosomal dorsal segment VIII and sometimes on segment V; hypostome with denticles arranged in rows; with 1 pair of posthypostomal setae; eyes and festoons present. Nymph: Anal groove posterior to the anus; eyes and festoons present; spiracular plates comma-shaped. Adult: Scutum ornate with rare exceptions; anal groove posterior to the anus; eyes and festoons present; spiracular plates in comma shape; spurs on coxae usually present; ventral plates absent in most males; porose areas present in females.

Genus Hyalomma

The following descriptions are based on Apanaskevich and colleagues (2008).

Larva: Eyes present; portion of scutum posterior to eyes 1/5 to 1/4 of scutal length; apex of spur on coxae I directed posteriorly or medially; narrower palps and hypostome; shorter legs. Nymph: Posterior margin of scutum broadly rounded with moderate posterolateral depressions on either side of its extremity; spiracular plates with relatively large, wide, blunt dorsal prolongation. Adult: Deep cervical grooves; in females scutum with sparse large punctations, small punctations usually very sparse or absent; narrow V-shaped genital operculum; preatrial fold of genital operculum flat or very slightly convex; posteromedial spur of coxa I broad and with blunt apex; males with broadly oval shape of conscutum; deep and long cervical grooves; short marginal grooves; large punctations sparse; smaller punctations normally sparse or absent; adanal plates distinctly curved medially; subanal plates moderate in size; dorsal prolongation of spiracular plates long.

Genus Rhipicentor

The following morphological descriptions are based on Cooper and Robinson (1908) and Clifford and Anastos (1960).

Larva: Palps short with 3 articles (article 1 absent); 3 marginal dorsal setae anterior to the sensilla sagittiformia; eyes present; idiosomal with 9 festoons. Adult: females with scutum as long as broad, with few punctations, posterior border sinuous; eyes present slightly anterior to the lateral angles; cervical grooves parallel; spiracular plates short, comma-shaped; basis capituli protuberant laterally, small cornua present. Male of Rhipicentor nuttalli has idiosoma oval, narrow in front, slightly concave just behind level of eyes; scutum covers entire dorsum, glabrous, polished, punctations not numerous, coarse and showing a tendency to arrange linearly; numerous fine punctations at posterior end of body immediately anterior to festoons; cervical grooves short and deep, crescentic with convexity outwards; marginal grooves well-defined, commencing a little distance behind the eyes and terminating at the external festoon on either side; posteromedian and accessory grooves shallow and ill-defined; eyes large and pale. Venter yellowish-brown with few scattered pale hairs; genital grooves parallel anteriorly, divergent behind coxae and extending to festoons; spiracles comma-shaped. Capitulum short (length 1.1 mm), basis capituli large, with pronounced lateral angles, cornua strong, short and blunt; palps short and broad; articles 2 and 3 rounded laterally; slight ventral retrograde tooth on article 3; hypostome slightly spatulate, dentition 3/3. Legs strong, coxa I with 2 strong spurs placed close together, the internal pointed, the external blunt; coxae II and III with very stumpy blunt spurs; coxa IV very large, with 2 long almost equal spurs, widely separated and slightly divergent.

Genus Rhipicephalus

The following morphological descriptions are based on Neumann (1900; 1901; 1904; 1905; 1907; 1911), Apanaskevich and colleagues (2013b), Horak and colleagues (2013), and Nava and colleagues (2018).

Larva: Eyes present, with 4 pairs of marginal dorsal setae anterior to the sensilla sagittiformia; idiosomal with 9 festoons; lateral sides of basis capituli acute or slightly angular. Nymph: Eyes present; basis capituli hexagonal, hypostomal dentition 3/3, small auriculae present in Rhipicephalus sanguineus (Latreille, 1806) and related species that forms the R. sanguineus group; anal groove distinct or indistinct. Female: Scutum inornate; eyes present; basis capituli dorsally hexagonal; palps short and round apically, dental formula 3/3 to 4/4; anal groove distinct or indistinct; spiracular plates rounded to elongated. Male: Eyes present; basis capituli hexagonal dorsally; small cornua present or absent; palps short, palpal articles II and III with short, retrograde, internal process; dental formula 3/3 to 4/4; anal groove distinct or indistinct; spiracular plates round to elongated; adanal plates present, some species with caudal appendage.

Genus Archaeocroton

The description presented below was that proposed by Dumbleton (1943) and by Kaufman (1972) for Archaeocroton sphenodonti.

Larva: Large elongate cervical grooves. Nymph: Not available. Adult: Idiosoma suboval in both, scutum light brown, inornate, with small and very numerous punctations evenly distributed; eyes absent. Male with cervical and marginal grooves, cervical grooves short, slightly divergent; lateral grooves distinct, incomplete, extending half the distance between the first festoons and scapulae; basis capitulum subtriangular, cornua distinct, blunt; palps elongate and somewhat thickened; hypostome spatulate, dentition 3/3 distally and 2/2 proximally, with large corona; 2 files with about 5–6 stout denticles and partial innerfile with 5 very fine denticles; all coxae with a single subtriangular spur; tarsi very elongate. Female with scutum subcordiform, broader than long, cervical groove present; cervical pits deep, slightly concave externally; cervical grooves short and slightly divergent; cornua extremely broad, very blunt; palps elongate, thickened, article (segment) 2 about twice as long as article (segment) 3; a pair of very large conical spurs on either side of the midline of the ventral basis capituli; hypostome spatulate, dentition 3/3 distally and 2/2 proximally, with large corona; 2 files with circa 5–6 stout denticles and partial innerfile with 5 very fine denticles; genital aperture opposite level of coxae II; genital groove divergent; spiracular plate subcircular, as wide as long; all coxae with a subtriangular spur that is as long as broad, and tarsi very slightly humped, noticeably elongate and without spurs.

Genus Anomalohimalaya

The following morphological descriptions are based on Hoogstraal and colleagues (1970) and Filippova and Bardzimashvily (1992).

Larva: Basis capituli dorsally 3.5 times as broad as long, the ventrally posteroexternal junctures are at an angle; dorsally with 2 small sensilla hastiformia, ventrally 1 pair post-hypostomal setae, palps 2 times as long as broad; scutum 1.7 times as broad as long; anterior emargination broad, shallow; scapulae slightly rounded; external margin gradually diverging to convex posterior margin; eyes are large, slightly convex, pale area in each posteroexternal juncture; festoons present. Nymph: The nymph of Anomalohimalaya cricetuli has a smooth nitidus scutum with closely moved lateral and cervical grooves, forming a narrow deep short furrow, whereas in 2 other species the scutum is dull, the furrow between the lateral and cervical grooves is short and nearly reaches posterolateral margins of the scutum. Shape and location of the lateral projections of the basis capituli corresponds to those of female. Anal valves equally get narrow forward and backward, whereas in A. lotozkyi they are narrower anteriorly; eyes absent in A. lamai. Adult: Basis capituli dorsally broadly quadrangular, externally converging to narrower, straight posterior margin; anteroventrally flanged; palps clavate, 2 times as long as broad, article I extended ventrointernally; eyes absent; scutum broadly pyriform, rugose, lacking lateral grooves, cervical grooves indistinct, punctations especially large and numerous. Basis capituli hexagonal in females; the dorsal scutum in A. cricetuli, is pointed posteriorly and the genital opening is U-shaped, whereas in 2 other species the scutum is rounded posteriorly and the genital opening is V-shaped. Anomalohimalaya cricetuli differs from A. lotozkyi in that it has less pointed and shorter lateral projections of the gnathosoma basis, apexes of which are moved forward from the posterior margin, and by concave laterally porous area. It differs from A. lama by the absence of the dorsal process on the spiracular plate, and a short tooth on coxae IV.

Genus Bothriocroton

The following morphological descriptions are based on Klompen and colleagues (2002), Barker and Walker (2014), and Beati and colleagues (2008).

Larva: Hypostomal dentition in the adults 2/2 or 3/3, internal row much smaller than other rows; 3 large wax glands lateral near setae s6 (= marginal dorsal setae Md3), and anterior to the first festoons; large wax glands on festoon 5 absent; eyes absent; idiosomal setation pattern generally as in other Metastriata; scutum more broad than long; leg and palpal chaetotaxy as in Amblyomma sensu lato. Nymph: Scutum similar to the females, with conspicuous posterolateral indentations formed by confluence of larger punctations; eyes absent; anal groove posterior to the anus; spiracular plates extruding from lateral body margins in Bothriocroton oudemansi. Adult: Basis capituli subpentagonal in shape; eyes absent, but large punctations could be mistaken for an eye; hypostomal dentition 3/3 to 4/4; scutum of the males with partial or complete lateral grooves, with white ornamentation in some species; trochanters with a single subterminal ventral spur (absent in B. glebopalma); coxae I with anterior projection visible in some species; anal groove posterior to the anus; large spiracular plates anterior to first festoon, extruding from lateral body margin in male and female of B. oudemansi.

Genus Cosmiomma

The following morphological descriptions are based on adults (Arthur, 1960b); immature stages are unknown.

Adult: Basis capituli subtriangular dorsally; palpal article 2 appreciably narrower than article 3, and about twice as long; enamel pigmentation on the palps, basis capituli, scutum, and legs; eyes well developed; 11 festoons in the female more or less clearly defined, with large spiracular plate abutting against the margins of the anterior festoons; female with anal groove encircling the anus and produced behind in a median groove; male with 1 pair of adanal plates, accessory and subanal plates absent. Coxa I with long external spur and prominent internal spur, divergent.

Genus Haemaphysalis

The following descriptions are based on Apanaskevich and colleagues (2007).

Larva: Eyes absent; scutum inornate; 2 marginal dorsal setae anterior to the sensilla sagittiformia on each side; article II of palps laterally produced beyond the basis capituli; idiosoma with 11 festoons; anal groove posterior to the anus. Nymph: Eyes absent; basis capituli rectangular dorsally; scutum inornate; article II of palps laterally produced; article III of palps with retrograde ventral spur; spiracular plate suboval; anal groove posterior to the anus. Adult: Article II of palps laterally produced; article III of palps with retrograde ventral spur; eyes absent; scutum inornate; article II of palps laterally produced; article III of palps with retrograde ventral spur; in females the scutum is 1.3 times as long as broad, cervical grooves narrow arcs extending 2/3 of total scutal length; posterior lip of genital aperture broadly U-shaped; spiracular plates varying in size, irregularly suboval or subcircular, dorsal projection short, broadly triangular; in males the spiracular plate is variable in size, usually slightly broader than long, suboval, dorsal projection triangular, submarginal row of perforations on spiracular plate complete; coxal pore absent. In male, the basis capituli rectangular dorsally; article II of palps laterally produced; article III of palps with retrograde ventral spur; marginal groove absent.

Genus Margaropus

The following morphological descriptions are based on Arthur (1960b), Clifford and Anastos (1960), Walker and Laurence (1973), and Walker and colleagues (2003).

Larva: 5 marginal dorsal setae, Md5, located anteriorly to the dorsal sensilla sagittiformia, all other larval morphology resembles those of the genera Dermacentor and Rhipicephalus. Nymph: Idiosoma with long setae; basis capituli 3 times as wide as long, with straight basal margin, rounded junctures, and divergent lateral margins; eyes present; palps 4 times as long as wide; segment I forming a slight pedicle; segments 2 and 3 of approximately equal length and subrectangular; apex more or less bluntly rounded; segment 3 ventrally with a short, wide spur not reaching basal margin of segment; hypostome similar with smaller corona and 3/3 dentition in files of 8 denticles; spiracular plates subcircular, with 6 large goblets in a circle. Adult: Festoons absent; in females the scutum is inornate, widest at midlength between the scapulae and the eyes, posterior margin bluntly pointed; eyes present which may be indistinct; porose areas vertically subtriangular; palpal articles 2 and 3 separated by a slight constriction; coxae conical, unarmed but for a small spur posteriorly on coxa I, tarsi elongate, narrow, tapering with a large apical hook-like projection; integument bears conspicuous hairs posteriorly; spiracular plate subcircular, 3 rows of large goblets around the ostium; males with expanded leg articles that are more or less deeply separated from each other; scutum with lateral margins convex, more strongly convergent anteriorly, bluntly rounded behind, about a third as long again as it is wide; spiracular plates similar to the females; a pair of adanal plates present; caudal appendage present in Margaropus winthemi, broad and has a hook on the ventral surface; hypostome about twice as long as broad, slightly notched in the mid-line distally, and behind a well-defined corona the dentition is 4/4. This species is distinguished from Rhipicephalus (Boophilus) spp. by the thick legs that are very conspicuous in males.

Genus Nosomma

The following morphological descriptions are based on Arthur (1965), Singh (1968), and Prakasan and Ramani (2007).

Larva: Basis capituli triangular dorsally, posterior margin slightly convex, lateral margins slightly sinuous and meet posterior margin to form sharp lateral points; ventrally basis triangular with posterior margin bow shaped; palps long and slender, reaching to the apex of hypostome, hypostome slender, dentition 2/2; eyes flat; cervical grooves shallow, narrow anteriorly but broadening posteriorly to almost reach the hind margin of scutum; dorsally without marginal grooves but with 9 distinct festoons. Nymph: Basis capituli dorsally triangular; posterior margin almost straight; posterolateral angle sharp and pointed. Ventrally posterior margin bow shaped; palps long and slender, reaching to the tip of hypostome, article 2 twice as long as article 3, dentition 2/2; posterior margin of scutum broadly rounded; eyes flat and situated at posterolateral corners of scutum, cervical grooves subparallel anteriorly and diverging posteriorly reaching posterior margin; dorsal integument with faint marginal grooves and 11 well marked festoons; spiracular plates oval. Adult: Nosomma resembles Dermacentor in the shape of the capitulum and in having short palps; palpal articles 1, 2, and 3 of Nosomma are unlike those of known Dermacentor species in the possession of long, broad, strong sabre-like hairs on their infra–internal margin. Basis capituli of female is almost twice as broad as long; cornua prominent, basal breadth exceeding their length, broadly rounded; idiosomal with distinct median and paramedian grooves on the dorsal surface, posterior extremity of median groove continuous with depressions separating parma from adjacent festoons; 11 festoons present. Basis capituli of male is rectangular dorsally; palps conical lacking basolateral salience; median ridge like dorsal palpal spur; hypostome reaching apex of palps; hypostomal denticles formula 4/4; scutum outline elongated oval, brownish, whitish ornamentation present; cervical grooves short and deep; pseudoscutum well marked; eyes prominently colored; 11 festoons present, festoon 2 dorsally separated by well-marked sutures; palpal article III more broad than long with a stronger ventral process, hypostomal dentition 3/3; coxa I with 2 separated spurs; coxae II–IV with small spurs; tarsus IV with 2 ventral spurs, the distal one stronger than the proximal; ventral plates represented by adanal and accessory subadanal plates tri-lobed, middle lobes come close to each other behind the anal groove; anal groove posterior to the anus; spiracular plates comma-shaped.

Genus Robertsicus

Baker and Burger (2018) did not repeat the description for Amblyomma elaphense when the new combination for Robertsicus elaphense was proposed, but we present the one previously detailed by Keirans and Degenhardt (1985).

Larva: Outline suboval, widest at midlength with 11 festoons; setae dorsally 13 pairs, all minute except for scutal central 1 (SC1); 2 central dorsal pairs; 8 marginal dorsal pairs, 2 of which are anterior to sensilla sagittiformia; supplementary setae absent; 3 scutal pairs; ventrally 15 pairs, 3 sternal pairs, 2 preanal pairs, 4–5 premarginal pairs, 5 marginal pairs, 1 pair on anal valves; palpal setae 10 on segment 4, 3 dorsally, 1 laterally, 2 ventrally on segment 3; 3 dorsally, 1 laterally, 2 ventrally on segment 2; 0 on segment 1; hypostome bluntly rounded apically with few minute hooklets, dental formula 2/2; scutum inornamented; eyes absent; cervical grooves and punctations absent; legs with small triangular external spur on coxae I–III, internal spurs absent; setae: coxa I with 3, coxae II and III with 2 setae each; Haller’s organ with roof bifurcate; anterior pit setae: 1 porose, 2 fines, 1 fine or perhaps setiform. Nymph: Small, suboval, about as wide as long; scutum with scale-like markings over the surface, otherwise as in female; capitulum dorsally broadly triangular, corona absent; ventrally with hypostomal dentition 2/2, a small corona of minute denticles apically; legs each with a very small bluntly rounded spur on coxae I–IV; spiracular plate suboval, without dorsal prolongation. Adult: Inornate, light brown. Male with scutum smooth, without cervical or marginal grooves, setae and punctations minute, inapparent under binocular microscopy; capitulum dorsally subtriangular, lacking cornua; ventrally with hypostomal dentition 2/2 throughout, apically with a large corona of fine denticles; palps elongate; legs each with a single triangular spur on coxae I–IV; Haller’s organ roof slit-like and slightly bifurcate medially, 5 anterior pit setae; spiracular plate suboval with a long narrow dorsal prolongation, globet cells minute. Female with scutum more broad than long, cordiform, smooth, without cervical grooves, setae and punctations minute; capitulum dorsally subtriangular, cornua absent; porose areas subcircular, shallow; ventrally with hypostomal dentition 2/2 (although the hypostome figured has a single supernumerary tooth between file 1 and 2 on the left side of the hypostome as viewed from above); legs with coxae as in male; genital aperture at level of coxae II; spiracular plate suboval with a short dorsal prolongation, goblet cells minute.

Genus Nuttalliella

The following morphological descriptions are based on Bedford (1931), Latif and colleagues (2012), and Mans and colleagues (2018).

Larva: Dorsum with a sclerotized scutum; cervical grooves and eyes absent; pre-anal groove present; anal plate with rows of denticles separated by the median post-anal groove; 5 posthypostomal setae present; apex of hypostome distinctly rounded, forming a ball-like structure, with 11 prominent denticles arranged in 2 rows. Nymph: Idiosoma circular; pseudoscutum with elevation between the cervical grooves; eyes absent; surface of alloscutum with dense-elevated and convoluted rosettes and setae in rosette pits; posthypostomal setae present; hypostomal denticles rudimentary; spiracular plates fenestrated and located posterior to coxa IV. Female: Idiosoma covered by leathery integument; scutum semi-sclerotized wider than long; preanal groove present; gnathosoma ventroapically, a pair of posthypostomal setae present; hypostomal denticles large and distinct arranged in 2 rows; palps 4-segmented; coxal organ absent; and spiracular plates fenestrated and located posterior to coxa IV. Male: Pseudoscutum present, covering most of the dorsum; chelicerae forming a unique rod-like structure similar to a spematodactyl in mites.

Medical and Veterinary Significance of Ticks

Ticks are obligate blood-sucking parasites with an almost worldwide distribution. As the second largest group of vectors of human disease agents (only trailing mosquitoes), ticks are among the most important vectors of pathogens causing disease in humans and other animals (Dantas-Torres et al., 2012). They are the most important ectoparasites of livestock in tropical and subtropical areas, and the diseases and direct damage caused by ticks are responsible for severe economic losses in livestock production (Jongejan and Uilenberg, 2004).

Human–tick interactions are extremely common resulting in a great impact on human health. Due to saliva secretion during blood feeding, ticks transmit pathogens, such as viruses, bacteria, protozoa, and helminths, readily to hosts. Aside from mere irritation, their bite can also lead to allergy and even severe toxic conditions, such as paralysis and toxicosis in humans and other animals. Infection with multiple tick-transmitted pathogens can occur in an individual host after exposure to co-infected ticks or multiple ticks infected with different pathogens. The coinfection of individual ticks is a relatively frequent phenomenon and the same tick species may be a vector for different pathogens (Milutinovic et al., 2008; Nicholson et al., 2010), which may partially explain variations in clinical presentation, pathogenicity, and host response to therapy.

Pathogens ingested by a single larval tick may be passed through to subsequent developmental stages (that is, nymph and adult) through transstadial transmission from host to host (also called horizontal transmission) and, if a female is infected, may eventually be spread to her offspring through vertical or transovarial transmission. Female ticks are extremely fecund and may lay thousands of eggs, which enables effective dissemination of infectious agents.

Wildlife and ticks are the main reservoirs and vectors of tickborne pathogens of medical and veterinary importance (Dantas-Torres et al., 2012b). Species of ticks that parasitize domestic animals are the most studied, while those that parasitize wildlife are still poorly understood as to their ability to transmit pathogens. Wild and domestic carnivores are considered the primary source of tickborne zoonotic agents affecting humans (Otranto et al., 2015).

Ticks and tickborne diseases have a zoogeographical range restricted by host movement and climatic factors. However, the increased mobility of humans and of domestic animals has resulted in a rapid extension of the zoogeographical ranges for many tick species and tick-transmitted pathogens. As such, the incidence of tickborne diseases in humans and animals has increased in the 21st century (Estrada-Peña and Jongejan, 1999; Guglielmone et al., 2006). Additional factors associated with the emergence or re-emergence of vector-borne diseases include global warming (and resultant climate change), increased outdoor recreation, global travel, urbanization, encroachment of human development on natural environments, deforestation, and habitat fragmentation, which together promote greater contact between ticks, wildlife, humans, and domestic animals (Beugnet and Chalvet-Monfray, 2013; Dantas-Torres, 2015).
The major zoonoses whose causative agents are transmitted by ticks are rickettsioses, borrelioses, ehrlichiosis, and babesiosis. Rickettsioses are mainly associated with ticks of the genera Amblyomma, Dermacentor, Ixodes, and Rhipicephalus, borrelioses to Ixodes and Ornithodoros, and ehrlichiosis and babesiosis mostly to Rhipicephalus (Barros-Battesti et al., 2006). These diseases and other zoonotic tickborne illnesses, such as those of viral origin, characterized by encephalitis and hemorrhagic fevers, are the major cause of host morbidity and mortality (Jongejan and Uilenberg, 2004; Dantas-Torres et al., 2012b). In the following sections, the main tickborne diseases of humans and other animals are summarized.

Anaplasmosis

Anaplasmosis is a disease caused by gram-negative bacteria of the order Rickettsiales, family Anaplasmataceae, and genus Anaplasma (Dumler et al., 2001).

Bovine anaplasmosis occurs in tropical, subtropical, and temperate regions of the world, and is caused by the intraerythrocytic rickettsia Anaplasma marginale, a member of the ehrlichial genogroup II (Dumler et al., 2001); A. marginale is transmitted biologically by ixodid ticks, by hematophagous insects, and mechanically by needles contaminated with blood of infected animals.

After inoculation of a suitable bovine host, and after an incubation period of 20–40 days, there is an increase in rickettsemia, resulting in anemia, weight loss, abortion, and death (Richey, 1981). The disease can have serious consequences, especially when susceptible animals are introduced into endemic areas. In this case, mortality may exceed 50%, causing serious problems to genetic breeding programs, based on the importation of animals from disease-free areas (Machado, 1995).

Combining tick control and vaccination results in the most effective measure against this disease (Palmer, 1989). Immunized cattle may develop persistent field infections, acting as reservoirs of Anaplasma marginale helping to maintain the pathogen circulation in endemic areas.

The most important species in dogs is Anaplasma platys, which mainly infects platelets and causes infectious canine cyclic thrombocytopenia (Ferreira et al., 2007). It is generally found in co-infections with Babesia and Ehrlichia, and Rhipicephalus sanguineus sensu lato is suspected to be a vector, though its role remains unproven (Dantas-Torres, 2008; Ribeiro et al., 2017). This pathogen is widespread on several continents but has a predilection for tropical and subtropical regions (Ferreira et al., 2007).

Anaplasma phagocytophilum is incriminated as the causal agent of the human granulocytic anaplasmosis (HGA) in the Northern Hemisphere, tickborne fever in cattle and sheep in Europe, and equine and canine granulocytic anaplasmosis in the United States (Woldehiwet, 2010; André, 2018).

Babesiosis

Babesiosis is caused by tick-transmitted intraerythrocytic protozoa of the order Piroplasmida, family Babesiidae, genus Babesia (see Figure 13). Babesia protozoa are one of the most common blood parasites in the world and they have a wide host range, including mammals and bird species (Schnittger et al., 2012). Hard ticks are the known vectors of these protozoa, such as Rhipicephalus sanguineus sensu lato that transmits B. vogeli (Gray et al., 2010; René et al., 2012; Silva et al., 2012).

The disease can occur in subclinical, acute, hyperacute, or chronic forms, ranging from mild clinical signs to fatal disease. Severity of illness depends on many factors, such as Babesia species and immunocompetence of the patient (Schetters et al., 1997; Gray et al., 2010; Yabsley and Shock, 2013).

Figure 13. Babesiosis life cycle. Babesiosis is caused by apicomplexan parasites of the genus Babesia. While more than 100 species have been reported, only a few have been identified as causing human infections, including B. microti, B. divergens, B. duncani, and a currently unnamed strain designated MO-1. — The Babesia microti life cycle involves 2 hosts, which includes a rodent, primarily the white-footed mouse Peromyscus leucopus and a tick in the genus Ixodes. During a blood meal, a Babesia-infected tick introduces sporozoites into the mouse host (1). Sporozoites enter erythrocytes and undergo asexual reproduction (budding) (2). In the blood, some parasites differentiate into male and female gametes although these cannot be distinguished at the light microscope level (3). The definitive host is the tick. Once ingested by an appropriate tick (4), gametes unite and undergo a sporogonic cycle resulting in sporozoites (5). Transovarial transmission (also known as vertical, or hereditary, transmission) has been documented for “large” Babesia spp. but not for the “small” babesiae, such as B. microti (A). — Humans enter the cycle when bitten by infected ticks. During a blood meal, a Babesia-infected tick introduces sporozoites into the human host (6). Sporozoites enter erythrocytes (B) and undergo asexual replication (budding) (7). Multiplication of the blood stage parasites is responsible for the clinical manifestations of the disease. Humans are, for all practical purposes, dead-end hosts and there is probably little, if any, subsequent transmission that occurs from ticks feeding on infected persons. However, human-to-human transmission is well recognized to occur through blood transfusions (8).
(Source: Division of Parasitic Diseases and Malaria, United States Centers for Disease Control and Prevention, 2017. Public domain.)

Bovine babesiosis (BB) is a tickborne disease of cattle caused by protozoan parasites of the genus Babesia (phylum Apicomplexa, order Piroplasmida). The principal species of Babesia that cause BB are: Babesia bovis, B. bigemina, and B. divergens. Other species that can infect cattle include B. major, B. ovata, B. occultans, and B. jakimovi. Rhipicephalus tick species are most commonly involved in the transmission of this disease, generally in tropical and subtropical countries (WOAH, 2021).

Canine babesiosis may be caused by several species of Babesia, which are usually classified as small and large Babesia. Small Babesia species include B. gibsoni, B. conradae, and B. microti-like (also referred to Theileria annae and B. vulpes, but these are nomina nuda, meaning that the scientific names are used but without the necessary accompanying scientific description), whereas large Babesia species include B. canis, B. vogeli, B. rossi, and an unclassified species (“Babesia sp. Coco”) found in dogs in North Carolina, United States (Citard et al., 1995; Schetters et al., 1997; Köster et al., 2015; Solano-Gallego et al., 2016). Babesia gibsoni is transmitted by Haemaphysalis longicornis Neumann, 1901 in Asia and possibly by blood exchange during dog fights. Babesia canis is transmitted by Dermacentor reticulatus in Europe, B. vogeli is transmitted by R. sanguineus sensu lato in tropical and subtropical regions, and B. rossi is transmitted by H. elliptica (Koch, 1844) in southern Africa (Uilenberg et al., 1989; Sasaki et al., 2007; Köster et al., 2015). The vectors of B. conradae and B. microti-like remain unknown.

Ehrlichiosis

Ehrlichiosis is a disease caused by several species of obligate intracellular gram-negative bacteria of the genus Ehrlichia that infect humans and other animals in different parts of the world (Dumler et al., 2001).

Human ehrlichiosis is caused by Ehrlichia chaffeensis (human monocytic ehrlichiosis), E. ewingii (human granulocytic ehrlichiosis), or E. muris eauclairensis (undetermined ehrlichiosis) (Dantas-Torres et al., 2012b; Pritt et al., 2017). Ehrlichia chaffeensis is the most common causative agent of human ehrlichiosis in the United States. It is maintained in a cycle that involves the white-tailed deer (Odocoileus virginianus) and the lone star tick Amblyomma americanum (Linnaeus, 1758), which play a role as primary reservoir and vector, respectively (Skotarczak, 2003; Yabsley, 2010). Even though white-tailed deer seem to be the main host for E. chaffeensis, serological and molecular evidence of infection by this agent has been reported in wild carnivores (André, 2018). Amblyomma americanum also transmits E. ewingii, while the vector of E. muris eauclairensis is Ixodes scapularis Say, 1821.

Canine monocytic ehrlichiosis (CME) is a life-threatening disease in dogs that requires rapid and accurate diagnosis in order to initiate appropriate therapy (Skotarczak, 2003). Ehrlichia canis, the agent of CME, infects monocytes and macrophages of domestic dogs and wild carnivores (Stich et al., 2008). Rhipicephalus sanguineus sensu lato and Dermacentor variabilis (Say, 1821) are the recognized vectors for E. canis (Johnson et al., 1998; Dantas-Torres, 2008). The disease is described around the world, but CME appears to be particularly prevalent in tropical regions where it is principally vectored by R. sanguineus sensu lato (Cicuttin et al., 2015). In South America, the occurrence of CME in tropical regions is related to the difference in vector competence. Populations of R. sanguineus sensu lato belonging to the tropical lineage are highly competent vectors of E. canis, while South American populations of R. sanguineus sensu stricto (= temperate lineage) are incompetent vectors of E. canis, which partly explains the scarcity or absence of CME in colder regions of South America (Nava et al., 2012; Moraes-Filho et al., 2015).

Lyme disease (or Lyme borreliosis)

Lyme borreliosis (LB) is the most frequent tickborne disease in the Northern Hemisphere. The disease is caused by spirochetes of the Borrelia burgdorferi sensu lato complex, which are transmitted by several tick species of the genus Ixodes (Gray et al, 2002; Rauter and Hartung, 2005). LB is recognized as the most commonly reported arthropod-borne disease in North America and Europe, accounting for thousands of new cases yearly in both regions (Piesman and Eisen, 2008; Marques, 2010; CDC, 2017).

In most cases, the tick must be attached to its mammalian host for 36 to 48 hours or more before the bacteria can be transmitted. Typical symptoms include fever, headache, fatigue, and a characteristic skin rash called erythema migrans (CDC, 2017). The complications of untreated LB in humans can be severe and disabling (Dennis and Hayes, 2002).

Rickettsioses

Tickborne rickettsioses are caused by intracellular bacteria belonging to the spotted fever group (SFG) of the genus Rickettsia and are among the oldest known vector-borne diseases of humans. The importance of the recognized rickettsial pathogens has increased in the past several years. Several species of tickborne rickettsiae that were considered nonpathogenic for decades are now associated with human infections, such as R. slovaca, R. aeschlimannii, R. massiliae, R. monacensis, and R. parkeri. New species of Rickettsia of undetermined pathogenicity continue to be detected in or isolated from ticks around the world (Labruna et al., 2011; Parola et al., 2013).

Ticks can be reservoirs and vectors for most species of Rickettsia. Bacteria remain in tick populations by transovarial and transstadial transmission. However, some rickettsiae may also be deleterious to ticks, such as R. rickettsii (Labruna, 2009).

Vertical transmission of rickettsial agents in arthropods helps to maintain the infection in nature, but for some species of rickettsiae, a life cycle including infected arthropods and 1 or more amplifying hosts is required to guarantee survival of the bacteria (Davoust et al., 2010). Humans are only occasional hosts for ticks and, thus, play no role in maintaining these bacteria in nature (Socolovschi et al., 2009). Rickettsia rickettsii is the most pathogenic Rickettsia species, and the disease caused by this agent is generally called Rocky Mountain spotted fever (RMSF), because it was first reported in the Rocky Mountain region of the United States (CDC, 2006). In Brazil, the disease is Brazilian spotted fever and has a high fatality rate (Oliveira et al., 2016). Despite the availability of accurate diagnostic tools and efficacious therapy, RMSF continues to be a life-threatening disease, with high lethality rate in several endemic geographic foci. The disease has been shown to have a complex ecology with participation of different vertebrate animals and tick species (CDC, 2006). Several tick species have been implicated as vectors of Rickettsia rickettsii accordingly to different geographic areas. While Dermacentor andersoni Stiles, 1908 and D. variablilis are the main vectors in the United States, ticks of the Amblyomma cajennense (Fabricius, 1787) species complex, such as A. cajennense sensu stricto and A. sculptum (Berlese, 1888), have been implicated as the most important vectors in South America, mainly in Brazil (Labruna et al., 2017). Moreover, R. sanguineus sensu lato has been implicated as a vector in Mexico and the United States (Dantas-Torres, 2007).

Rickettsia parkeri is another SFG rickettsia recognized as a human pathogen, with several confirmed cases in the United States. The first confirmed human infection with R. parkeri was reported in the United States in 2004, more than 60 years after this bacterium was first isolated in that country, from the Gulf Coast tick Amblyomma maculatum Koch, 1844 (Paddock et al., 2004). Rickettsia parkeri rickettsiosis can be difficult to distinguish from RMSF and other spotted fevers, especially during the early stages. A retrospective study provided serological evidence that a number of cases previously diagnosed as RMSF in the United States were actually caused by R. parkeri, suggesting that both rickettsioses have been misidentified in that country. This disease is characteristically less severe than RMSF and almost always associated with an inoculation eschar (an ulcerated, necrotic lesion) at the site of tick attachment (Paddock et al., 2004).

Several other SFG rickettsia (for example, Rickettsia conorii) are important human pathogens and may also infect and cause disease in animals, such as dogs, in Europe and elsewhere in the world. Comprehensive information about other rickettsiae infection humans can be found elsewhere (Dantas-Torres et al., 2012a; Parola et al., 2013; Portillo et al., 2015).

Epidemiological Tick Control and Preventative Measures

Human behavior (for example, sitting on logs, gathering wood, leaning against trees, and walking) might increase the risk of exposure to ticks (Lane et al., 2004). For instance, people visiting forested areas might be exposed to hard ticks whereas people entering tick-infested caves and encountering rodent burrows might be exposed to soft ticks.

Strategies to reduce populations of vector ticks through area-wide application of acaricides and control of tick habitats (for example, clearing leaf litter and brush) have been effective in small-scale trials. Community based, integrated, tick management strategies may prove to be an effective public health response to reduce the incidence of tickborne infections. However, limiting exposure to ticks is currently the most effective method of prevention (Dantas-Torres, 2007; Pinter et al., 2011).

Whenever possible, areas that are likely to be infected with ticks should be avoided, particularly in the seasons in which larvae and nymphs feed and can be found in abundance. Ticks are commonly found in humid and shady environments, especially grassy or litter areas with low lying vegetation.

From a practical perspective, it is unreasonable to assume that a person can eliminate all activities that may result in tick exposure. Therefore, measures should be aimed at personal protection (Dantas-Torres, 2007; Piesman and Eisen, 2008; CDC, 2006; 2017). The following measures are recommended:

• When walking through forested areas or with shrubby vegetation, avoid places potentially infested by ticks, and if possible, walk in the center of trails.
• Wear long-sleeved shirts and long trousers (not shorts) and tuck pant bottoms into tops of socks or boots. Wear light colored clothing which makes it easier to find crawling ticks.
• Check often for ticks especially after leaving forested areas. Common sites of attachment include the groin, the underarms, the nape of the neck, around the waist, and behind the knee.
• Examine children more often, paying special attention to the head, neck, and ears. Teach them to avoid tall grass and low brush.
• Do not let pets roam freely in these areas, and if they are allowed to go to these spots, check them daily, especially if allowed indoors. Free roaming pets may carry ticks of all life stages and can be infected with tickborne diseases. This is rather important for companion animals living in close contact with humans.
• To remove attached ticks, use fine-tipped tweezers or shield your fingers with a tissue, paper towel, or rubber gloves. Avoid removing ticks with bare hands.
• Grasp the tick with the tweezers as close as possible to the surface of the skin, turn it gently, and from time to time pull upward with steady, even pressure.
• Do not squeeze, crush, or puncture the body of the tick because its fluids (saliva, body fluids, gut contents) may contain infectious organisms.
• Save the tick for identification and potentially test for pathogens. This may help your doctor make an accurate diagnosis if you become sick.

Supplemental Materials

Supplemental documents are available online including keys for the identification of tick families and genera, and a list of extant species described chronologically from 1758 to October 2019.

Reviewers

Agustín Estrada-Peña, Department of Animal Health, Faculty of Veterinary Medicine, University of Zaragoza, Zaragoza, Spain.

Alberto A. Guglielmone, Instituto Nacional de Tecnología Agropecuaria, Estación Experimental Agropecuaria, Rafaela, Argentina.

Literature Cited

André, M. R. 2018. Diversity of Anaplasma and Ehrlichia/Neoehrlichia agents in terrestrial wild carnivores worldwide: Implications for human and domestic animal health and wildlife conservation. Frontiers in Veterinary Science 5: 293. doi: 10.3389/fvets.2018.00293

Apanaskevich, D. A., and M. A. Apanaskevich. 2018. Description of a new species of Amblyomma Koch, 1844 (Acari: Ixodidae), parasite of deer (Artiodactyla: Cervidae) and wild pigs (Artiodactyla: Suidae) in the Philippines. Systematic Parasitology 95: 415–425. doi: 10.1007/s11230-018-9797-x

Apanaskevich, D. A., and M. A. Apanaskevich. 2015b. Description of new Dermacentor (Acari: Ixodidae) species from Malaysia and Vietnam. Journal of Medical Entomology 52: 156–162. doi: 10.1093/jme/tjv001

Apanaskevich, D. A., and M. A. Apanaskevich. 2015a. Description of a new Dermacentor (Acari: Ixodidae) species from Thailand and Vietnam. Journal of Medical Entomology 52: 806–812. doi: 10.1093/jme/tjv067

Apanaskevich, D. A., and M. A. Apanaskevich. 2016. Description of two new species of Dermacentor Koch, 1844 (Acari: Ixodidae) from Oriental Asia. Systematic Parasitology 93: 159–171. doi: 10.1007/s11230-015-9614-8

Apanaskevich, D. A., and M. A. Apanaskevich. 2015c. Reinstatement of Dermacentor bellulus (Acari: Ixodidae) as a valid species previously confused with D. taiwanensis and comparison of all parasitic stages. Journal of Medical Entomology 52: 573–595. doi: 10.1093/jme/tjv034

Apanaskevich, D. A., and S. E. Bermúdez. 2013a. Description of a new Dermacentor (Acari: Ixodidae) species, a parasite of wild mammals in Central America. Journal of Medical Entomology 50: 1,190–1,201. doi: 10.1603/ME13121

Apanaskevich, D. A., and S. E. Bermúdez. 2017. Description of a new species of Ixodes Latreille, 1795 (Acari: Ixodidae) and redescription of I. lasallei Méndez and Ortiz, 1958, parasites of agoutis and pacas (Rodentia: Dasyproctidae, Cuniculidae) in Central and South America. Systematic Parasitology 94: 463–475. doi: 10.1007/s11230-017-9718-4

Apanaskevich, D. A., and H. E. Lemon. 2018. Description of a new species of Ixodes Latreille, 1795 (Acari: Ixodidae) and redescription of I. priscicollaris Schulze, 1932, parasites of New Guinea rodents (Rodentia: Muridae). Systematic Parasitology 95: 373–382. doi: 10.1007/s11230-018-9786-0

Apanaskevich, D. A., I. G. Horak, and J.-L. Camicas. 2007. Redescription of Haemaphysalis (Rhipistoma) elliptica (Koch, 1844), an old taxon of the Haemaphysalis (Rhipistoma) leachi group from East and southern Africa, and of Haemaphysalis (Rhipistoma) leachi (Audouin, 1826) (Ixodida, Ixodidae). Onderstepoort Journal of Veterinary Research 74: 181–208. doi: 10.4102/ojvr.v74i3.122

Apanaskevich, D. A., I. G. Horak, and L. K. Mulumba-Mfumu. 2013b. A new species of Rhipicephalus (Acari: Ixodidae), a parasite of red river hogs and domestic pigs in the Democratic Republic of Congo. Journal of Medical Entomology 50: 479–84. doi: 10.1603/ME12266

Apanaskevich, D. A., A. L. Schuster, and I. G. Horak. 2008. The genus Hyalomma, VII:. Redescription of all parasitic stages of H. (Euhyalomma) dromedarii and H. (E.) schulzei (Acari: Ixodidae). Journal of Medical Entomology 45: 817–831. doi: 10.1093/jmedent/45.5.817

Arthur, D. R. 1956. The morphology of the British Prostriata with particular reference to Ixodes hexagonus Leach II 1. Parasitology 46: 261–307. doi: 10.1017/s0031182000026512

Arthur D. R. 1960a. A review of some ticks (Acarina: Ixodidae) of sea birds, Part II: The taxonomic problems associated with the Ixodes auritulus–percavatus group of species. Parasitology 50: 199–226. doi: 10.1017/s0031182000025294

Arthur, D. R. 1965. A revision of Nosomma monstrosum (Nuttall and Warburton, 1908) Ixodoidea: Ixodidae. Parasitology 55: 391–400. doi: 10.1017/s0031182000068864

Arthur, D. R. 1960b. Ticks: A monograph of the Ixodoidea, Part V: On the genera Dermacentor, Anocentor, Cosmiomma, Boophilus and Margaropus. London, United Kingdom, Cambridge University Press, 251 p.

Ash, A., A. Elliot, S. Godfrey, H. Burmej, et al. 2017. Morphological and molecular description of Ixodes woyliei n. sp. (Ixodidae) with consideration for co-extinction with its critically endangered marsupial host. Parasites and Vectors 10: 70. doi: 10.1186/s13071-017-1997-8

Bakkes, D. K., D. De Klerk, A. A. Latif, and B. J. Mans. 2018. Integrative taxonomy of Afrotropical Ornithodoros (Ornithodoros) (Acari: Ixodida: Argasidae). Ticks and Tick-Borne Diseases 9: 1,006–1,037. doi: 10.1016/j.ttbdis.2018.03.024

Barbieri, F. S., S. C. Chacón, M. B. Labruna, D. M. Barros-Battesti, et al. 2007. Topographical and numerical study of the idiosomal integumentary structures of the larva of four Neotropical species of Amblyomma Koch, 1844 (Acari: Ixodidae). Systematic Parasitology 68: 57–70. doi: 10.1007/s11230-006-9078-y

Barker, D. 2019. Ixodes barkeri n. sp. (Acari: Ixodidae) from the short-beaked echidna, Tachyglossus aculeatus, with a revised key to the male Ixodes of Australia, and list of the subgenera and species of Ixodes known to occur in Australia. Zootaxa 4658: 331–342. doi: 10.11646/zootaxa.4658.2.7

Barker, S. C., and T. D. Burger. 2018. Two new genera of hard ticks, Robertsicus n. gen. and Archaeocroton n. gen., and the solution to the mystery of Hoogstraal’s and Kaufman’s “primitive” tick from the Carpathian Mountains. Zootaxa 4500(4): 543–552. doi: 10.11646/zootaxa.4500.4.4

Barker, S. C., and A. Murrell. 2002. Phylogeny, evolution and historical zoogeography of ticks: A review of recent progress. Experimental and Applied Acarology 28: 55–68. doi: 10.1023/a:1025333830086

Barker, S. C., and A. R. Walker. 2014. Ticks of Australia: The species that infest domestic animals and humans. Zootaxa 3816: 001–144. doi: 10.11646/zootaxa.2316.1.1

Barros-Battesti, D. M., M. Arzua, and G. H. Bechara. 2006. Carrapatos de importância médico–veterinária da Região Neotropical: Um Guia Ilustrado para Identificação de Espécies. Vox/ICTTD-3/Butantan, São Paulo, Brazil, 223 p.

Barros-Battesti, D. M., G. A. Landulfo, H. R. Luz, A. Marcili, et al. 2015. Ornithodoros faccinii n. sp. (Acari: Ixodida: Argasidae) parasitizing the frog Thoropa miliaris (Amphibia: Anura: Cycloramphidae) in Brazil. Parasites and Vectors 8: 268. doi: 10.1186/s13071-015-0877-3

Barros-Battesti, D. M., D. G. Ramirez, G. A. Landulfo, J. L. H. Faccini, et al. 2013. Immature argasid ticks: Diagnosis and keys for neotropical region. Revista Brasileira de Parasitologia Veterinária 22: 443–456. doi: 10.1590/S1984-29612013000400002

Beati, L., J. E. Keirans, L. A. Durden, and M. D. Opiang. 2008. Bothriocroton oudemansi (Neumann, 1910) n. comb. (Acari: Ixodida: Ixodidae), an ectoparasite of the western longbeaked echidna in Papua New Guinea: Redescription of the male and first description of the female and nymph. Systematic Parasitology 69: 185–200. doi: 10.1007/s11230-007-9115-5

Bedford, G. A. H. 1931. Nuttalliella namaqua, a new genus and species of tick. Parasitology 23: 230–232. doi: 10.1017/S0031182000013573

Beugnet, F., and K. Chalvet-Monfray. 2013. Impact of climate change in the epidemiology of vector-borne diseases in domestic carnivores. Comparative Immunology, Microbiology and Infectious Diseases 36: 559–66. doi: 10.1016/j.cimid.2013.07.003

Burger, T. D., R. Shao, L. Beati, H. Miller, et al. 2012. Phylogenetic analysis of ticks (Acari: Ixodida) using mitochondrial genomes and nuclear rRNA genes indicates that the genus Amblyomma is polyphyletic. Molecular Phylogenetics and Evolution 64: 45–55. doi: 10.1016/j.ympev.2012.03.004

Camicas, L. J., J. P. Hervey, F. Adam, and P.-C. Morel. 1998. Les tiques du monde (Acarida, Ixodida): Nomenclature, stades décrits, hôtes, répartition. ORSTOM, Paris, 233 p.

Carret, C., F. Walas, B. Carcy, N. Grande, et al. 1999. Babesia canis canis, Babesia canis vogeli, Babesia canis rossi: Differentiation of three subspecies by restriction fragment length polymorphism analysis on amplified small subunit ribosomal RNA genes. Journal of Eukaryotic Microbiology 46: 298–303. doi: 10.1111/j.1550-7408.1999.tb05128.x

CDC (United States Centers for Disease Control and Prevention). 2006. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichiosis, and anaplasmosis, United States. Morbidity and Mortality Week Report 55: RR-4.

CDC (United States Centers for Disease Control and Prevention). 2017. Tickborne diseases of the United States. A reference manual for health care providers. 4th Edition, 20 p.

Chitimia-Dobler, L., B. C. de Araujo, B. Ruthensteiner, T. Pfeffer, et al. 2017. Amblyomma birmitum a new species of hard tick in Burmese amber. Parasitology 144: 1,441–1,448. doi: 10.1017/S0031182017000853

Chitimia-Dobler, L., T. Pfeffer, and J. A. Dunlop. 2018. Haemaphysalis cretacea a nymph of a new species of hard tick in Burmese amber. Parasitology 145: 1,440–1,451. doi: 10.1017/S0031182018000537

Cicuttin, G. L., E. L. Tarragona, M. N. Salvo, A. J. Mangold, et al. 2015. Infection with Ehrlichia canis and Anaplasma platys (Rickettsiales: Anaplasmataceae) in two lineages of Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) from Argentina. Ticks and Tick-Borne Diseases 6: 724–729. doi: 10.1016/j.ttbdis.2015.06.006

Clifford, C. M., and G. Anastos. 1960. The use of chaetotaxy in the identification of larval ticks (Acarina: Ixodidae). Journal of Parasitology 46: 567–578. doi: 10.2307/3274939

Clifford, C. M., G. Anastos, and A. Elbl. 1961. The larval ixodid ticks of the eastern United States (Acarina: Ixodidae). Miscellaneous Publications of the Entomological Society of America 2: 213–237.

Clifford, C. M., G. M. Kohls, and D. E. Sonenshine. 1964. The systematics of the subfamily Ornithodorinae (Acarina: Argasidae), I: The genera and subgenera. Annals of Entomological Society of America 57: 429–437. doi: 10.1093/aesa/57.4.429

Clifford, C. M., D. E. Sonenshine, J. E. Keirans, and G. M. Kohls. 1973. Systematics of the subfamily Ixodinae (Acarina: Ixodidae), 1. The subgenera of Ixodes. Annals of the Entomological Society of America 66: 489–500. doi: 10.4182/BHJB6050.2-1.3

Cooley, R. A. 1946. The genera Boophilus, Rhipicephalus, and Haemaphysalis (Ixodoidea) of the New World. National Institute of Health Bulletin 187: 1–54.

Cooley, R. A., and G. M. Kohls. 1944. The Argasidae of North America, Central America and Cuba. American Midland Naturalist 1: 152. doi: 10.5962/bhl.title.4511

Cooley, R. A., and G. M. Kohls. 1945. The genus Ixodes in North America. National Institute of Health Bulletin 184: 1–246. doi: 10.1093/jmammal/27.4.399

Cooley, R. A., and G. M. Kohls. 1940. Two new species of Argasidae (Acarina: Ixodoidea). Public Health Reports 55: 925–933. doi: 10.2307/4583300

Cooper, B. A., and L. E. Robinson. 1908. On six new species of Ixodidae, including a second species of the new genus Rhipicentor N. and W. Proceedings of the Cambridge Philosophical Society 14: 457–470.

Dantas-Torres, F. 2008. Canine vector-borne diseases in Brazil. Parasites and Vectors 1: 25. doi: 10.1186/1756-3305-1-25

Dantas-Torres, F. 2015. Climate change, biodiversity, ticks and tick-borne diseases: The butterfly effect. International Journal for Parasitology: Parasites and Wildlife. 4: 452–461. doi: 10.1016/j.ijppaw.2015.07.001

Dantas-Torres, F. 2007. Rocky Mountain spotted fever. Lancet Infectious Diseases 7: 724–732. doi: 10.1016/S1473-3099(07)70261-X

Dantas-Torres, F. 2018. Species concepts: What about ticks? Trends in Parasitology 34: 1,017–1,026. doi: 10.1016/j.pt.2018.09.009

Dantas-Torres, F., B. B. Chomel, and D. Otranto. 2012a. Ticks and tick-borne diseases: A One Health perspective. Trends in Parasitology 28: 437–446. doi: 10.1016/j.pt.2012.07.003

Dantas-Torres, F., J. M. Venzal, L. F. O. Bernardi, R. L. Ferreira, et al. 2012b. Description of a new species of bat-associated argasid tick (Acari: Argasidae) from Brazil. Journal of Parasitology 98: 36–45. doi: 10.1645/GE-2840.1

Davoust, B., O. Mediannikov, J. L. Marie, C. Socolovschi, et al. 2010. Are vertebrates reservoir hosts for Rickettsia? Bulletin de l’Académie vétérinaire de France 163: 291–302.

De la Cruz, J. 1976. Notas adicionales a la fauna de las garrapatas (Ixodoidea) de Cuba, V: Una nueva especie de genero Antricola Cooley & Kohls 1942 (Argasidae). Poeyana 151: 1–8.

De la Cruz, J. 1978. Notas adicionales a la fauna de las garrapatas (Ixodoidea) de Cuba, VI: Cuatro nuevas especies del género Antricola Cooley y Kohls, 1942 (Argasidae; Ornithodorinae). Poeyana 184: 1–17.

De La Cruz, J. 1973. Notas sobre las garrapatas del gênero Antricola Cooley y Kohls, 1942 (Ixodiformes, Argasidae) con la descripción de una nueva especie. Academia de Ciencias de Cuba 44: 1–13.

De la Cruz, J., and A. Estrada-Peña. 1995. Four new species of Antricola ticks (Argasidae: Antricolinae) from bat guano in Cuba and Curação. Acarologia 36: 277–286.

Du, C.-H., Y. Sun, and Z. T. Shao. 2018. Description of Haemaphysalis (Alloceraea) kolonini sp. nov., a new species in subgenus Alloceraea Schulze (Ixodidae: Haemaphysalis) in China. Acta Parasitologica 63: 678–691. doi: 10.1515/ap-2018-0080

Dumbleton, L. J. 1943. A new tick from the tuatara (Sphenodon punctatus). New Zealand Journal of Science and Technology 24: 185–190.

Dumler, J. S., A. F. Barbet, C. P. J. Bekker, G. A. Dasch, et al. 2001. Reorganization of genera in the families Rickettsiaceae and Anaplasmataceae in the order Rickettsiales; unification of some species of Ehrlichia with Anaplasma, Cowdria with Ehrlichia with Neorickettsia, descriptions of six new species combinations and designation of Ehrlichia equi and HE agent as subjective synonyms of Ehrlichia phagocytophila. International Journal of Systematic and Evolutionary Microbiology 51: 2,145–2,165. doi: 10.1099/00207713-51-6-2145

Durden, L. A., and J. E. Keirans 1996. Nymphs of the Genus Ixodes (Acari: Ixodidae) of the United States: Taxonomy, Identification Key, Distribution, Hosts, and Medical/Veterinary Importance. Entomological Society of America, Lanham, Maryland, United States, 95 p.

Estrada-Peña, A., and J. De La Fuente. 2018. The fossil record and the origin of ticks revisited. Experimental and Applied Acarology 75: 255–261. doi: 10.1007/s10493-018-0261-z

Estrada-Peña, A., and F. Jongejan. 1999. Ticks feeding on humans: A review of records on human-biting Ixodoidea with special reference to pathogen transmission. Experimental and Applied Acarology 23: 685–715. doi: 10.1023/A:1006241108739

Estrada-Peña, A., A. J. Mangold, S. Nava, J. M. Venzal, et al. 2010. A review of the systematics of the tick family Argasidae (Ixodida). Acarologia 50: 317–333. doi: 10.1051/acarologia/20101975

Estrada-Peña, A., S. Nava, and T. Petney. 2014. Description of all the stages of Ixodes inopinatus n. sp. (Acari: Ixodidae). Ticks and Tick-Borne Diseases 5: 734–743. doi: 10.1016/j.ttbdis.2014.05.003

Estrada-Peña, A., J. M. Venzal, D. M. Barros-Battesti, V. C. Onofrio, et al. 2004. Three new species of Antricola (Acari: Argasidae) from Brazil, with a key to the known species in the genus. Journal of Parasitology 90: 490–498. doi: 10.1645/GE-172R

Ferreira, R. F., A. M. F. Cerqueira, A. M. Pereira, C. M.Guimarães, et al. 2007. Anaplasma platys diagnosis in  dogs: Comparison between morphological and molecular tests. International Journal of Applied Research in Veterinary Medicine 5: 113.

Feldman-Muhsam, B. 1973. Autogeny in soft ticks of the genus Ornithodoros (Acari: Argasidae). Journal of Parasitology 59: 536–539. doi: 10.2307/3278790

Filippova, N. A., and E. A. Bardzimashvily. 1992. [Anomalohimalaya cricetuli (Ixodoidea: Ixodidae) in the mountains of middle Asia and differential diagnostics of female and nymph.] Parazitologiia 26: 403–408. [In Russian.]

Filippova, N. A., and I. V. Panova. 1978. [Anomalohimalaya lotozkyi sp. n., a new species of ixodid ticks from the Peter the First Range (Ixodoidea, Ixodidae).] Parazitologiia 12: 391–399. [In Russian.]

Flores, J. P., and D. G. Solís. 2018. First record of the spinose ear tick (Otobius megnini) on the Baird’s tapir. International Journal of Acarology 44: 189–191. doi: 10.1080/01647954.2018.1490347

Gray, J. S., L. V. VonStedingk, and M. E. A. Gurtelschmid. 2002. Transmission studies of Babesia microti in Ixodes ricinus ticks and gerbils. Journal of Clinical Microbiology 40: 1,259–1,263. doi: 10.1128/jcm.40.4.1259-1263.2002

Gray, J. S., A. Zintl, A. Hildebrandt, K.-P. Hunfeld, et al. 2010. Zoonotic babesiosis: Overview of the disease and novel aspects of pathogen identity. Ticks and Tick-Borne Diseases 1: 3–10. doi: 10.1016/j.ttbdis.2009.11.003

Groves, M. G., G. L. Dennis, H. L. Amyx, and D. L. Huxsoll. 1975. Transmission of Ehrlichia canis to dogs by ticks (Rhipicephalus sanguineus). American Journal of Veterinary Research 36: 937–940.

Guglielmone, A. A., L. Beati, D. M. Barros-Battesti, M. B. Labruna, et al. 2006. Ticks (Ixodidae) on humans in South America. Experimental and Applied Acarology 40: 83–100. doi: 10.1007/s10493-006-9027-0

Guglielmone, A. A., R. G. Robbins, D. A. Apanaskevich, T. N. Petney, et al. 2010. The Argasidae, Ixodidae and Nuttalliellidae (Acari: Ixodida) of the world: A list of valid species names. Zootaxa 2528: 1–28. doi: 10.11646/zootaxa.2528.1.1

Guglielmone, A. A., R. G. Robbins, D. A. Apanaskevich, T. N. Petney, et al. 2014. The hard ticks of the world (Acari: Ixodida: Ixodidae). Springer, London, United Kingdom, 738 p.

Guglielmone, A. A., M. E. Sánchez, L. G. Franco, S. Nava, et al. 2016. Sitio web “Nombres de Especies de Garrapatas Duras.” 8º Congreso de AgroInformática. Jornadas Argentinas de Informática 45: 195–201.

Guglielmone, A. A., M. P. J. Szabó, J. R. S. Martins, and Estrada-Peña A. 2006. Diversidade e importância de carrapatos na sanidade animal. In D. M. Barros-Battesti, M. Arzua, and G. H. Bechara, eds. Carrapatos de importância médico veterinária da Região Neotropical: Um guia ilustrado para identificação de espéciesVox/ICTTD-3/Butantan, São Paulo, Brazil, p. 115–138.

Guo, T., Y. Sun, G. Xu, and L. A. Durden. 2017. Ixodes kangdingensis (Acari: Ixodidae), a new species from the Siberian weasel, Mustela sibirica (Carnivora: Mustelidae) in China. Parasitology Open 3: 1–8. doi: 10.1017/pao.2017.7

Guzmán-Cornejo, C., and R. G. Robbins. 2010. The genus Ixodes (Acari: Ixodidae) in Mexico: Adult identification keys, diagnoses, hosts, and distribution = El género Ixodes (Acari: Ixodidae) en México: Claves de identificación para adultos, diagnosis, huéspedes y distribución. Revista mexicana de biodiversidad 81.

Halperin, J. J., P. Baker, and G. P. Wormser. 2013. Common misconceptions about Lyme disease. American Journal of Medicine 126: 264. doi: 10.1016/j.amjmed.2012.10.008

Heath, A. C. G., and R. L. Palma. 2017. A new species of tick (Acari: Ixodidae) from seabirds in New Zealand and Australia, previously misidentified as Ixodes eudyptidis. Zootaxa 4324: 285–314. doi: 10.11646/zootaxa.4324.2.4

Herrin, C. S., and D. E. Beck. 1965. Observations on the biology, anatomy, and morphology of Otobius lagophilus Cooley and Kohls. Brigham Young University Science Bulletin, Biological Series 6: 1–19.

Hoogstraal, H., and K. C. Kim. 1985. Tick and mammal coevolution, with emphasis on Haemaphysalis. In K. C. Kim, ed. Coevolution of Parasitic Arthropods and Mammals. Wiley Inter-Science, New York, New York, United States, p. 505–568.

Hoogstraal, H., and H. Trapido. 1966. Studies on southeast Asian Haemaphysalis ticks (Ixodoidea, Ixodidae): Species described by Supino in 1897 from Burma, with special reference to H. (Rhipistma) asiaticus (= H. dentipalpis Warburton and Nuttall). Journal of Parasitology 52: 1,172–1,187. doi: 10.2307/3276365

Hoogstraal, H., M. N. Kaiser, and R. M. Mitchell. 1970. Anomalohimalaya lama, new genus and new species (Ixodoidea: Ixodidae), a tick parasitizing rodents, shrews, and hares in the Tibetan highland of Nepal. Annals of the Entomological Society of America 63: 1,576–1,585. doi: 10.1093/aesa/63.6.1576

Hoogstraal, H., B. L. Lim, and G. Anastos. 1969. Haemaphysalis (Kaiseriana) bispinosa Neumann (Ixodoidea, Ixodidae): Evidence for consideration as an introduced species in the Malay Peninsula and Borneo. Journal of Parasitology 55: 1,075–1,077. doi: 10.2307/3277178

Hoogstraal, H., H. Trapido, and G. M. Kohls. 1965. Studies on southeast Asian Haemaphysalis ticks (Ixodoidea, Ixodidae): The identity, distribution and hosts of H. (Kaiseriana) hystricis Supino. Journal of Parasitology 51: 467–480. doi: 10.2307/3275974

Horak, I. G., D. A. Apanaskevich, and E. K. Kariuki. 2013. A new species of Rhipicephalus (Acari: Ixodidae), a parasite of giraffes in Kenya. Journal of Medical Entomology 50: 685–690. doi: 10.1603/ME12257

Horak, I. G., H. Lutermann, K. Medger, D. A. Apanaskevich, et al. 2012. Natural hosts of the larvae of Nuttalliella sp. (N. namaqua?) (Acari: Nuttalliellidae). Onderstepoort Journal of Veterinary Research 79: 405. doi: 10.4102/ojvr.v79i1.405

Horak, I. G., H. Heyne, R. Williams, G. J. Gallivan, et al. 2018. The Ixodid Ticks (Acari: Ixodidae) of Southern Africa. Springer, Basel, Switzerland, 676 p. doi: 10.1007/978-3-319-70642-9_4

Hornok, S., T. Görföl, P. Estók, V. T. Tu, et al. 2016. Description of a new tick species, Ixodes collaris n. sp. (Acari: Ixodidae), from bats (Chiroptera: Hipposideridae, Rhinolophidae) in Vietnam. Parasites and Vectors 9: 332. doi: 10.1186/s13071-016-1608-0

Hornok, S., J. Kontschán, D. Kováts, R. Kovács, et al. 2014. Bat ticks revisited: Ixodes ariadnae sp. nov. and allopatric genotypes of I. vespertilionis in caves of Hungary. Parasites and Vectors 7: 202. doi: 10.1186/1756-3305-7-202

Hosseini-Chegeni, A., J. Khedri, Z. Telmadarraiy, and F. Faghihi. 2018. Otobius megnini (Acari: Argasidae) in Iran: Exotic or established? Persian Journal of Acarology 7: 209–216. doi: 10.22073/pja.v7i2.34812

Johnson, E. M., S. A. Ewing, R. W. Barker, J. C. Fox, et al. 1998. Experimental transmission of Ehrlichia canis (Rickettsiales: Ehrlichieae) by Dermacentor variabilis (Acari: Ixodidae). Veterinary Parasitology 74: 277–288. doi: 10.1016/s0304-4017(97)00073-3

Jones, E. K., C. M. Clifford, J. E. Keirans, and G. M. Kohls. 1972. The ticks of Venezuela (Acarina: Ixodoidea) with a key to the species of Amblyomma in the Western Hemisphere. Brigham Young University Science Bulletin: Biological Series 17: 1–40.

Jongejan, F., and G. Uilenberg. 2004. The global importance of ticks. Parasitology 129: S3–S14. doi: 10.1017/s0031182004005967

Kaufman, T. S. 1972. A revision of the genus Aponomma Neumann, 1899 (Acarina: Ixodidae). Thesis (PhD), University of Maryland, College Park, Maryland, United States, 389 p.

Keirans, J. E., and C. M. Clifford. 1975. Nothoaspis reddelli, new genus and new species (Ixodoidea: Argasidae), from a bat Cave in Mexico. Annals of the Entomological Society of America 68: 81–85. doi: 10.1093/aesa/68.1.81

Keirans, J. E., and W. G. Degenhardt. 1985. Aponomma elaphense Price, 1959 (Acari: Ixodidae): Diagnosis of the adults and nymph with first description of the larva. Proceedings of the Biological Society of Washington 98: 711–717.

Keirans, J. E., and J. M. Pounds. 2003. An annotated bibliography of the spinose ear tick, Otobius megnini (Dugès, 1883) (Acari: Ixodida: Argasidae) 1883–2000. Systematic and Applied Acarology 13: 1–68.

Keirans, J. E., C. M. Clifford, H. Hoogstraal, and E. R. Easton. 1976. Discovery of Nuttalliella namaqua Bedford (Acarina: Ixodoidea: Nuttalliellidae) in Tanzania and redescription of the female based on scanning electron microscopy. Annals of the Entomological Society of America 69: 926–932. doi: 10.1093/aesa/69.5.926

Keirans, J. E., H. Hoogstraal, and C. M. Clifford. 1979. Observations on the subgenus Argas (Ixodoidea: Argasidae: Argas), 16: Argas (A.) moreli, new species, and keys to Neotropical species of the subgenus. Journal of Medical Entomology 15: 246–252. doi: 10.1093/jmedent/15.3.246

Keirans, J. E., D. R. King, and R. D. Sharrad. 1994. Aponomma (Bothriocroton) glebopalma, n. subgen., n. sp., and Amblyomma glauert n. sp. (Acari: Ixodida: Ixodidae), parasites of monitor lizards (Varanidae) in Australia. Journal of Medical Entomology 31: 132–147. doi: 10.1093/jmedent/31.1.132

Klompen, J. S. H., and J. H. Oliver. 1993. Systematic relationships in the soft ticks (Acari: Ixodida: Argasidae). Systematic Entomology 18: 313–331. doi: 10.1111/j.1365-3113.1993.tb00669.x

Klompen, J. S. H., Keirans, J. E., N. A. Filippova, and J. H. Oliver. 1996. Idiosomal lyrifissures, setae, and small glands as taxonomic characters and potential indicators of ancestral segmentation patterns in larval Ixodidae (Acari: Ixodida). International Journal of Acarology 22: 113–134. doi: 10.1080/01647959608684086

Klompen, J. S. H., and D. Grimaldi. 2001. First Mesozoic record of a parasitiform mite: A larval argasid tick in Cretaceous amber (Acari: Ixodida: Argasidae). Annals of Entomological Society of America 94: 10–15. doi: 10.1603/0013-8746(2001)094[0010:FMROAP]2.0.CO;2

Klompen, J. S. H., S. J. Dobson, and S. C. Barker. 2002. A new subfamily, Bothriocrotoninae n. subfam., for the genus Bothriocroton Keirans, King & Sharrad, 1994 status amend. (Ixodida: Ixodidae), and the synonymy of Aponomma Neumann, 1899 with Amblyomma Koch, 1844. Systematic Parasitology 53: 101–107. doi: 10.1023/A:1020466007722

Koch, C. L. 1844. Systematische Übersicht über die Ordnung der Zecken. Archive fur Naturgeschichte 10: 217–239. doi: 10.5962/bhl.part.29560

Kohls, G. M. 1956a. Eight new species of Ixodes from Central and South America (Acarina: Ixodidae). Journal of Parasitology 42: 636–649. doi: 10.2307/3274884

Kohls, G. M. 1956b. The identity of Ixodes boliviensis Neumann, 1904 and Ixodes bicornis Neumann, 1906. Proceedings of the Entomological Society of Washington 58: 232–233.

Kohls, G. M. 1957. Ixodes downsi, a new species of tick from a cave in Trinidad, British West Indies (Acarina: Ixodidae). Proceedings of the Entomological Society of Washington 59: 257–264.

Kohls, G. M. 1969. Ixodes taglei n. sp. (Acarina: Ixodidae) a parasite of the deer, Pudu pudu (Wol.), in Chile. Journal of Medical Entomology 6: 439–442. doi: 10.1093/jmedent/6.3.280

Kohls, G. M. 1953. Ixodes venezuelensis, a new species of tick from Venezuela, with notes on Ixodes minor Neumann, 1902 (Acarina: Ixodidae). Journal of Parasitology 39: 300–303. doi: 10.2307/3273954

Kohls, G. M., and C. M. Clifford. 1967. Ixodes (Hemixodes) uruguayensis, new subgenus, new species (Acarina: Ixodidae) from small rodents in Uruguay. Annals of the Entomological Society of America 60: 391–394.

Kohls, G. M., and C. M. Clifford. 1962. Ixodes tiptoni, a new species of tick from Panama (Acarina: Ixodidae). Journal of Parasitology 48: 182–184. doi: 10.2307/3275560

Kohls, G. M., and C. M. Clifford. 1964. Ornithodoros (Alectorobius) boliviensis sp. n. (Acarina: Argasidae) from bats and houses in Bolivia. Journal of Parasitology 50: 792–796. doi: 10.2307/3276204

Kohls, G. M., and C. M. Clifford. 1966. Three new species of Ixodes from Mexico and description of the male of I. auritulus auritulus Neumann, I. conepati Cooley and Kohls, and I. lasallei Méndez and Ortiz (Acarina: Ixodidae). Journal of Parasitology 52: 810–820. doi: 10.2307/3276462

Kohls, G. M., and H. Hoogstraal. 1961. Observations on the subgenus Argas (Ixodoidea, Argasidae, Argas), 4: A. neghmei, new species, from poultry houses and human habitations in northern Chile. Annals of the Entomological Society of America 54: 844–851. doi: 10.1093/aesa/54.6.844

Kohls, G. M., C. M. Clifford, and E. K. Jones. 1969a. The systematics of the subfamily Ornithodorinae (Acarina: Argasidae), IV: Eight new species of Ornithodoros from the Western Hemisphere. Annals of the Entomological Society of America 62: 1,035–1,043. doi: 10.1093/aesa/62.5.1035

Kohls, G. M., H. Hoogstraal, C. M. Clifford, and M. N. Kaiser. 1970. The subgenus Persicargas (Ixodoidea, Argasidae, Argas), 9: Redescription and New World records of Argas (P.) persicus (Oken), and resurrection, redescription, and records of A. (P.) radiatus Railliet, A. (P.) sanchezi Dugès,and A. (P.) miniatus Koch, New World ticks misidentified as A. (P.) persicus. Annals of the Entomological Society of America 63: 590–606. doi: 10.1093/aesa/63.2.590

Kohls, G. M., D. E. Sonenshine, and C. M. Clifford. 1969b. Ixodes (Exopalpiger) jonesae sp. n. (Acarina: Ixodidae), a parasite of rodents in Venezuela. Journal of Parasitology 55: 447–452. doi: 10.2307/3277433

Kohls, G. M., D. E. Sonenshine, and C. M. Clifford. 1965. The systematics of the subfamily Ornithodorinae (Acarina: Argasidae), II: Identification of the larvae of the Western Hemisphere and descriptions of three new species. Annals of the Entomological Society of America 58: 331–364. doi: 10.1093/aesa/58.3.331

Köster, L. S., R. G. Lobetti, and P. Kelly. 2015. Canine babesiosis: A perspective on clinical complications, biomarkers, and treatment. Veterinary Medicine (Auckland) 6: 119–128. doi: 10.2147/VMRR.S60431

Krawczak, F. S., T. F. Martins, C. S. Oliveira, L. C. Binder, et al. 2015. Amblyomma yucumense n. sp. (Acari: Ixodidae), a parasite of wild mammals in southern Brazil. Journal of Medical Entomology 52: 28–37. doi: 10.1093/jme/tju007

Kwak, M. L., C. Madden, and L. Wicker. 2018. Ixodes heathi n. sp. (Acari: Ixodidae), a co-endangered tick from the critically endangered mountain pygmy possum (Burramys parvus), with notes on its biology and conservation. Experimental and Applied Acarology 76: 413–419. doi: 10.1007/s10493-018-0312-5

Labruna, M. B. 2009. Ecology of Rickettsia in South America. Annals of the New York Academy of Sciences 1166: 156–166. doi: 10.1111/j.1749-6632.2009.04516.x

Labruna, M. B., M. Amaku, A. Metzner, A. Pinter, et al. 2003. Larval behavioral diapause regulates life cycle of Amblyomma cajennense (Acari: Ixodidae) in southeast Brazil. Journal of Medical Entomology 40: 171–178. doi: 10.1603/0022-2585-40.2.170

Labruna, M. B., N. Kasai, F. Ferreira, J. L. H. Faccini, et al. 2002. Seasonal dynamics of ticks (Acari: Ixodidae) on horses in the State of São Paulo, Brazil. Veterinary Parasitology 105: 65–77. doi: 10.1016/s0304-4017(01)00649-5

Labruna, M. B., F. S. Krawczak, M. Gerardi, L. C. Binder, et al. 2017. Isolation of Rickettsia rickettsii from the tick Amblyomma sculptum from a Brazilian spotted fever endemic area in the Pampulha Lake region, southeastern Brazil. Veterinary Parasitology: Regional Studies and Reports 8: 82–85. doi: 10.1016/j.vprsr.2017.02.007

Labruna, M. B., S. Nava, A. Marcili, A. R. M. Barbieri, et al. 2016. A new argasid tick species (Acari: Argasidae) associated with the rock cavy, Kerodon rupestris Wied-Neuwied (Rodentia: Caviidae), in a semiarid region of Brazil. Parasites and Vectors 9: 511. doi: 10.1186/s13071-016-1796-7

Lane, R. S., D. B. Steinlein, and J. Mun. 2004. Human behaviors elevating exposure to Ixodes pacificus (Acari: Ixodidae) nymphs and their associated bacterial zoonotic agents in a hardwood forest. Journal of Medical Entomology 41: 239–248. doi: 10.1603/0022-2585-41.2.239

Latif, A. A., J. F. Putterill, D. G. D. Klerk, R. Pienaar, et al. 2012. Nuttalliella namaqua (Ixodoidea: Nuttalliellidae): First description of the male, immature stages and re-description of the female. PLoS One 7: e41651. doi: 10.1371/journal.pone.0041651

Machado, R. Z. 1995. Emprego do ensaio imunoenzimático indireto (ELISA Teste) no estudo da resposta imune humoral de bovinos importados e premunidos contra a tristeza parasitária. Revista Brasileira de Parasitologia Veterinária 4 (Suplemento 1): 217.

Mans, B. J., M. H. Castro, R. Pienaar, D. Klerk, et al. 2016. Ancestral reconstruction of tick lineages. Ticks and Tick-Borne Diseases 7: 509–535. doi: 10.1016/j.ttbdis.2016.02.002

Mans, B. J., J. Featherston, M. Kvas, K.-A. Pillay, et al. 2019. Argasid and ixodid systematics: Implications for soft tick evolution and systematics, with a new argasid species list. Ticks and Tick-Borne Diseases 10: 219–240. doi: 10.1016/j.ttbdis.2018.09.010

Mans, B. J., D. Klerk, R. Pienaar, M. H. Castro, et al. 2012. The mitochondrial genomes of Nuttalliella namaqua (Ixodoidea: Nuttalliellidae) and Argas africolumbae (Ixodoidae: Argasidae): Estimation of divergence dates for the major tick lineages and reconstruction of ancestral blood-feeding characters. PLoS One 7: e49461. doi: 10.1371/journal.pone.0049461

Mans, B. J., D. Klerk, R. Pienaar, and A. A. Latif. 2014. The host preferences of Nuttalliella namaqua (Ixodoidea: Nuttalliellidae): A generalist approach to surviving multiple host-switches. Experimental and Applied Acarology 62: 233–240. doi: 10.1007/s10493-013-9737-z

Mans, B. J., D. Klerk, R. Pienaar, and A. A. Latif. 2011. Nuttalliella namaqua, a living fossil and closest relative to the ancestral tick lineage: Implications for the evolution of blood-feeding in ticks. PLoS One 6: e23675. doi: 10.1371/journal.pone.0023675

Marques A. 2010. Lyme disease: A review. Current Allergy and Asthma Reports 10: 13–20. doi: 10.1007/s11882-009-0077-3

Martins, T. F., M. B. Labruna, A, J. Mangold, M. M. Cafrune, et al. 2014. Taxonomic key to nymphs of the genus Amblyomma (Acari: Ixodidae) in Argentina, with description and redescription of the nymphal stage of four Amblyomma species. Ticks and Tick-Borne Diseases 5: 753–70. doi: 10.1016/j.ttbdis.2014.05.007

Martins, T. F., H. R. Luz, S. Muñoz-Leal, D. G. Ramirez, et al. 2019. A new species of Amblyomma (Acari: Ixodidae) associated with monkeys and passerines of the Atlantic rainforest biome, Southeastern Brazil. Ticks and Tick-Borne Diseases 10: 101259. doi: 10.1016/j.ttbdis.2019.07.003

Martins, T. F., V. C. Onofrio, D. M. Barros-Battesti, and M. B. Labruna. 2010. Nymphs of the genus Amblyomma (Acari: Ixodidae) of Brazil: descriptions, redescriptions, and identification key. Ticks and Tick-Borne Diseases 1: 75–99. doi: 10.1016/j.ttbdis.2010.03.002

Milutinovic, M., T. Masuzawa, S. Tomanovic, Z. Radulovic, et al. 2008. Borrelia burgdorferi sensu lato, Anaplasma phagocytophilum, Francisella tularensis and their coinfections in host-seeking Ixodes ricinus ticks collected in Serbia. Experimental and Applied Acarology 45: 171–183. doi: 10.1007/s10493-008-9166-6

Moraes-Filho, J., F. S. Krawczak, F. B. Costa, J. F. Soares, et al. 2015. Comparative evaluation of the vector competence of four South American populations of the Rhipicephalus sanguineus group for the bacterium Ehrlichia canis, the agent of Canine Monocytic Ehrlichiosis. PLoS One 10: e0139386. doi: 10.1371/journal.pone.0139386

Muñoz-Leal, S., F. L. Toledo, J. M. Venzal, A. Marcili, et al. 2017. Description of a new soft tick species (Acari: Argasidae: Ornithodoros) associated with stream-breeding frogs (Anura: Cycloramphidae: Cycloramphus) in Brazil. Ticks and Tick-Borne Diseases 8: 682–692. doi: 10.1016/j.ttbdis.2017.04.015

Muñoz-Leal, S., F. A. Terrassini, A. Marcili, G. M. B. Oliveira, et al. 2019. A third species of Nothoaspis Keirans & Clifford 1975 (Acari: Argasidae): Nothoaspis setosus (Kohls, Clifford & Jones, 1969) n. comb. Systematic Parasitology 96: 595–602. doi: 10.1007/s11230-019-09873-9

Muñoz-Leal, S., J. M. Venzal, D. González-Acuña, S. Nava, et al. 2016. A new species of Ornithodoros (Acari: Argasidae) from desert areas of northern Chile. Ticks and Tick-Borne Diseases 7: 901–910. doi. 10.1016/j.ttbdis.2016.04.008

Muñoz-Leal, S., J. M. Venzal, S. Nava, M. Reyes, et al. 2018. The geographic distribution of Argas (Persicargas) miniatus and Argas (Persicargas) persicus (Acari: Argasidae) in America, with morphological and molecular diagnoses from Brazil, Chile and Cuba. Ticks and Tick-Borne Diseases 9: 44–56. doi: 10.1016/j.ttbdis.2017.10.009

Nava, S., L. Beati, M. B. Labruna, A. G. Cáceres, et al. 2014a. Reassessment of the taxonomic status of Amblyomma cajennense (Fabricius, 1787) with the description of three new species, Amblyomma tonelliae n. sp., Amblyomma interandinum n. sp. and Amblyomma patinoi n. sp., and reinstatement of Amblyomma mixtum Koch, 1844, and Amblyomma sculptum Berlese, 1888 (Ixodida: Ixodidae). Ticks and Tick-Borne Diseases 5: 252–276. doi: 10.1016/j.ttbdis.2013.11.004

Nava, S., L. Beati, J. M. Venzal, M. B. Labruna, et al. 2018. Rhipicephalus sanguineus (Latreille, 1806): Neotype designation, morphological re-description of all parasitic stages and molecular characterization. Ticks and Tick-Borne Diseases 9: 1,573–1,585. doi: 10.1016/j.ttbdis.2018.08.001

Nava, S., M. Mastropaolo, A. J. Mangold, T. F. Martins, et al. 2014b. Amblyomma hadanii n. sp. (Acari: Ixodidae), a tick from northwestern Argentina previously confused with Amblyomma coelebs Neumann, 1899. Systematic Parasitology 88: 261–272. doi: 10.1007/s11230-014

Nava, S., M. Mastropaolo, J. M. Venzal, A. J. Mangold, et al. 2012. Mitochondrial DNA analysis of Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) in the Southern Cone of South America. Veterinary Parasitology 190: 547–555. doi: 10.1016/j.vetpar.2012.06.032

Nava, S., J. M. Venzal, D. González-Acuña, T. F. Martins, et al. 2017. Ticks of the Southern Cone of America: Diagnosis, Distribution, and Hosts with Taxonomy, Ecology and Sanitary Importance. Academic Press/Elsevier, London, United Kingdom, 348 p.

Nava, S., J. M. Venzal, F. A. Terassini, A. J. Mangold, et al. 2010. Description of a new argasid tick (Acari: Ixodida) from bat caves in Brazilian Amazon. Journal of Parasitology 96: 1,089–1,101. doi: 10.1645/GE-2539.1

Neumann, L. G. 1913. Arachnides, I: Ixodidae. Voyage de Ch. Alluaud et R. Jeannel en Afrique orientale (1911–1912). Resultats scientifiques, Paris: Librarie Albert Schultz 31: 25–35.

Neumann, L. G. 1911. Ixodidae. In Das Tierreich, herausg. v. T. E. Schulze, im Auftrage der Königlich Preußischen Akademie der Wissenschaften zu Berlin. Friedlander, Berlin, Germany, 169 p.

Neumann, L. G. 1901. Revisión de la famille des Ixodidés, 2e mémoire. Mémoires de la Societé Zoologique de France 14: 249–372.

Neumann, L. G. 1899. Révision de la famille des Ixodidés, 3e mémoire. Mémoires de la Societé Zoologique de France 12: 107–294.

Neumann, L. G. 1904. Notes sur les Ixodidés, II. Archives de Parasitologie 8: 444–464.

Neumann, L. G. 1905. Notes sur les Ixodidés, III. Archives de Parasitologie 9: 225–241.

Neumann, L. G. 1906. Notes sur les Ixodidés, IV. Archives de Parasitologie 10: 195–219.

Neumann, L. G. 1907. Quatre espèces nouvelles d’ixodidés. Notes from the Leyden Museum 29: 88–100.

Nicholson, W. L., K. E. Allen, J. H. McQuiston, E. B. Breitschwerdt, et al. 2010. The increasing recognition of rickettsial pathogens in dogs and people. Trends Parasitology 26: 205–212. doi: 10.1016/j.pt.2010.01.007

Nuttall, G. H. F., and C. Warburton. 1908. A new genus of Ixodoidea together with a description of eleven new species of ticks. Proceedings of the Cambridge Philosophical Society 14: 392–416.

Oliveira, S. V., J. N. Guimarães, G. C. Reckziegel, B. M. C. Neves, et al. 2016. An update on the epidemiological situation of spotted fever in Brazil. Journal of Venomous Animals and Toxins including Tropical Diseases 22: 22. doi: 10.1186/s40409-016-0077-4

Oliver, J. H. 1989. Biology and systematics of ticks (Acari: Ixodida). Annual Review of Ecology and Systematics 20: 397–430. doi: 10.1146/annurev.es.20.110189.002145

Otranto, D., C. Cantacessi, F. Dantas-Torres, E. Brianti, et al. 2015. The role of wild canids and felids in spreading parasites to dogs and cats in Europe, Part I: Protozoa tickborne agents. Veterinary Parasitology 213: 12–23. doi: 10.1016/j.vetpar.2015.04.022

Paddock, C. D., J. W. Sumner, J. A. Comer, S. R. Zaki, et al. 2004. Rickettsia parkeri: A newly recognized cause of spotted fever rickettsiosis in the United States. Clinical Infectious Diseases 38: 805–811. doi: 10.1086/381894

Palmer, G. H. 1989. Anaplasma vaccines. In I. G. Wright, ed. Veterinary Protozoan and Hemoparasite Vaccines. CRC Press, Boca Raton, Florida, United States, p. 1–29.

Parola, P., C. D. Paddock, C. Socolovschi, M. B. Labruna, et al. 2013. Update on tick-borne rickettsioses around the world: A geographic approach. Clinical Microbiology Reviews 26: 657–702. doi: 10.1128/CMR.00032-13

Peñalver, E., A. Arillo, X. Delclòs, D. Peris, et al. 2017. Ticks parasitised feathered dinosaurs as revealed by Cretaceous amber assemblages. Nature Communications 8: 1,924. doi: 10.1038/s41467-017-01550-z

Piesman, J., and L. Eisen. 2008. Prevention of tick-borne diseases. Annual Review of Entomology 53: 323–343. doi: 10.1146/annurev.ento.53.103106.093429

Pinter, A., A. C. França, C. E. Souza, C. Sabbo, et al. 2011. Febre Maculosa Brasileira. BEPA (Boletim Epidemiológico Paulista) 8 (Suplemento): 31 p.

Portillo, A., S. Santibáñez, L. García-Álvarez, A. M. Palomar, et al. 2015. Rickettsioses in Europe. Microbes and Infection 17: 834–848. doi: 10.1016/j.micinf.2015.09.009.

Prakasan, K., and N. Ramani. 2007. Two new species of ixodid ticks (Acarina: Ixodida) from Kerala, India. International Journal of Zoological Research 3: 169–177. doi: 10.3923/ijzr.2007.169.177

Pritt, B. S., M. E. J. Allerdice, L. M. Sloan, C. D. Paddock, et al. 2017. Proposal to reclassify Ehrlichia muris as Ehrlichia muris subsp. muris subsp. nov. and description of Ehrlichia muris subsp. eauclairensis subsp. nov., a newly recognized tick-borne pathogen of humans. International Journal of Systematic and Evolutionary Microbiology 67: 2,121–2,126. doi: 10.1099/ijsem.0.001896

Ramírez, D. G., G. A. Landulfo, V. C. Onofrio, S. M. Simons, et al. 2016. Laboratory life cycle of Ornithodoros brasiliensis (Acari: Argasidae): An endemic tick from southern Brazil. Ticks and Tick-Borne Diseases 7: 730–733. doi: 10.1016/j.ttbdis.2016.03.001

Raoult, D., and P. Parola. 2008. Rocky Mountain spotted fever in the USA: A benign disease or a common diagnostic error? Lancet Infectious Diseases 8: 587–589. doi: 10.1016/S1473-3099(08)70210-X

Rauter, C., and T. Hartung. 2005. Prevalence of Borrelia burgdorferi sensu lato genospecies in Ixodes ricinus ticks in Europe: A meta-analysis. Applied and Environmental Microbiology 71: 7,203–7,216. doi: 10.1128/AEM.71.11.7203-7216.2005

René, M., J. Chêne, J. P. Beaufils, C. Valiente Moro, et al. 2012. First evidence and molecular characterization of Babesia vogeli in naturally infected dogs and Rhipicephalus sanguineus ticks in southern France. Veterinary Parasitology 187: 399–407. doi: 10.1016/j.vetpar.2012.01.030

Ribeiro, C. M., A. C. Matos, T. Azzolini, E. R. Ossos, et al. 2017. Molecular epidemiology of Anaplasma platys, Ehrlichia canis and Babesia vogeli in stray dogs in Paraná, Brazil. Pesquisa Veterinária Brasileira 37: 129–136. doi: 10.1590/S0100-736X2017000200006

Richey, E. J. 1981. Bovine anaplasmosis. In R. S. Howard, ed. Current Veterinary Therapy Food Animal Practice. Saunders, Philadelphia, Pennsylvania, United States, p. 767–772.

Robbins, R. G., and J. E. Keirans. 1992. Systematics and Ecology of the Subgenus Ixodiopsis (Acarina: Ixodidae: Ixodes). [Thomas Say Foundation Monograph 14]. Entomological Society of America, Lanham, Maryland, United States, 159 p.

Rubel, F., K. Brugger, M. Pfeffer, L. Chitimia-Dobler, et al. 2016. Geographical distribution of Dermacentor marginatus and Dermacentor reticulatus in Europe. Ticks and Tick-Borne Diseases 7: 224–233. doi: 10.1016/j.ttbdis.2015.10.015

Sasaki, M., O. Omobowale, M. Tozuka, K. Ohta, et al. 2007. Molecular survey of Babesia canis in dogs in Nigeria. Journal of Veterinary Medical Science 69: 1,191–1,193. doi: 10.1292/jvms.69.1191

Schnittger, L., A. E. Rodriguez, M. Florin-Christensen, and D. A. Morrison. 2012. Babesia: A world emerging. Infection, Genetics and Evolution 12: 1,788–1,809. doi: 10.1016/j.meegid.2012.07.004

Schulze, P. 1937. Anocentor columbianus n. g. n. sp. (Ixod.). Zoologischer Anzeiger 120: 24–27.

Schulze, P. 1933. Die arten der Zeckengattung Dermacentor s. l. aus Europe, Asien und Neu-Guinea. Zeitschrift für Parasitenkunde 6: 416–431.

Schulze, P. 1939. Zur Zeckenfauna Burma. Zeitschrift für Parasitenkunde 10: 722–728.

Schulze, P. 1935. Zur Zeckenfauna Formosas. Zoologischer Anzeiger 112: 233–237.

Silva, A. B., A. P. Costa, J. C. Sá, F. B. Costa, et al. 2012. Detecção molecular de Babesia canis vogeli em cães e em Rhipicephalus sanguineus na mesorregião do oeste maranhense, Nordeste brasileiro. Ciência Animal Brasileira 13: 388–395.

Singh, K. R. P. 1968. Description of the nymph and the larva of Nosomma monstrosum (Nuttall & Warburton, 1908). Parasitology 58: 461–463. doi: 10.1017/S003118200006947X

Skotarczak, B. 2003. Canine ehrlichiosis. Annals of Agricultural and Environmental Medicine 10: 137–141.

Socolovschi, C., O. Mediannikov, D. Raoult, and P. Parola. 2009. The relationship between spotted fever group Rickettsiae and ixodid ticks. Veterinary Research 40: 34. doi: 10.1051/vetres/2009017

Solano-Gallego, L., A. Sainz, X. Roura, A. Estrada-Peña, et al. 2016. A review of canine babesiosis: the European perspective. Parasites and Vectors 9: 336. doi: 10.1186/s13071-016-1596-0

Sonenshine, D. E. 1991. Biology of Ticks, volume1. Oxford University Press, New York, New York, United States, 447 p.

Sonenshine, D. E., and R. M. Roe. 2013. Biology of Ticks, Volume 2, 2nd edition. Oxford University Press, Oxford, United Kingdom, 540 p.

Stich, R. W., J. J. Schaefer, W. G. Bremer, G. R. Needham, et al. 2008. Host surveys, ixodid tick biology and transmission scenarios as related to the tick-borne pathogen, Ehrlichia canis. Veterinary Parasitology 158: 256–273. doi: 10.1016/j.vetpar.2008.09.013

Sun, Y., R. Xu, Z. Liu, M. Wu, et al. 2019. Ornithodoros (Ornithodoros) huajianensis sp. nov. (Acari, Argasidae), a new tick species from the Mongolian marmot (Marmota bobak sibirica), Gansu Province in China. International Journal for Parasitology: Parasites and Wildlife 9: 209–217. doi: 10.1016/j.ijppaw.2019.05.001

Tomlinson, J. A., and D. A. Apanaskevich. 2019. Two new species of Haemaphysalis Koch, 1844 (Acari: Ixodidae) in the H. (Rhipistoma) spinulosa subgroup, parasites of carnivores and hedgehogs in Africa. Systematic Parasitology 96: 485–509. doi: 10.1007/s11230-019-09860-0

Trape, J. F., G. Diatta, C. Arnathau, I. Bitam, et al. 2013. The epidemiology and geographic distribution of relapsing fever borreliosis in West and North Africa, with a review of the Ornithodoros erraticus complex (Acari: Ixodida). PLoS One 8: e78473. doi: 10.1371/journal.pone.0078473

Uilenberg G., F. F. J. Franssen, N. M. Perié, and A. A. M. Spanjer. 1989. Three groups of Babesia canis distinguished and a proposal for nomenclature. Veterinary Quarterly 11: 33–40. doi: 10.1080/01652176.1989.9694194

Venzal, J. M., A. Estrada-Peña, A. J. Mangold, D. González-Acuña, et al. 2008. The Ornithodoros (Alectorobius) talaje species group (Acari: Ixodida: Argasidae): Description of Ornithodoros (Alectorobius) rioplatensis n. sp. from southern South America. Journal of Medical Entomology 45: 832–840. doi: 10.1603/0022-2585(2008)45[832:TOATSG]2.0.CO;2

Venzal, J. M., D. González-Acuña, S. Muñoz-Leal, A. J. Mangold, et al. 2015. Two new species of Ornithodoros (Ixodida; Argasidae) from the Southern Cone of South America. Experimental and Applied Acarology 66: 127–139. doi: 10.1007/s10493-015-9883-6

Venzal, J. M., V. C. Onofrio, D. M. Barros-Battesti, and M. Arzua. 2006. Família Argasidae: Características gerais, comentários e chaves para gêneros e espécies. In D. M. Barros-Battesti, M. Arzua, and G. H. Bechara, eds. Carrapatos de importância médico–veterinária da Região Neotropical: Um guia ilustrado para identificação de espécies. Vox/ICTTD-3/Butantan, São Paulo, Brazil, p. 13–27.

Venzal, J. M., N. Santiago, D. González-Acuña, A. J. Mangold, et al. 2013. A new species of Ornithodoros (Acari: Argasidae), parasite of Microlophus spp. (Reptilia: Tropiduridae) from northern Chile. Ticks and Tick-Borne Diseases 4: 128–132. doi: 10.1016/j.ttbdis.2012.10.038

Venzal, J. M., N. Santiago, A. J. Mangold, M. Mastropaolo, et al. 2012. Ornithodoros quilinensis sp. nov. (Acari, Argasidae), a new tick species from the Chacoan region in Argentina. Acta Parasitologica 57: 329–336. doi: 10.2478/s11686-012-0034-5

Vongphayloth, K., J. C. Hertz, K. Lakeomany, D. A. Apanaskevich, et al. 2018. The genus Dermacentor (Acari: Ixodidae) in Laos: A review and update of species records. Journal of Medical Entomology 55: 1,047–1,050. doi: 10.1093/jme/tjy041

Walker, D. H. 2007. Rickettsiae and rickettsial infections: The current state of knowledge. Clinical Infectious Diseases 45, supplement I: S39–S44. doi: 10.1086/518145

Walker, J. B., and Laurence, B. R. 1973. Margaropus wileyi sp. nov. (Ixodoidea, Ixodidae), a new species of tick from the reticulated giraffe. Onderstepoort Journal of Veterinary Research 40: 13–21.

Walker, J. B., A. Bouattour, J.-L. Camicas, A. Estrada-Peña, et al. 2003. Ticks of Domestic Animals in Africa: A Guide to Identification of Species. ICTTD-2/Atalanta, Houten, Netherlands, 221 p.

WOAH (World Organisation for Animal Health). 2021. Bovine babesiosis.

Woldehiwet, Z. 2010. The natural history of Anaplasma phagocytophilum. Veterinary Parasitology 167: 108–122. doi: 10.1016/j.vetpar.2009.09.013

Yabsley, M. J. 2010. Natural history of Ehrlichia chaffeensis: Vertebrate hosts and tick vectors from the United States and evidence for endemic transmission in other countries. Veterinary Parasitology 167: 136–148. doi: 10.1016/j.vetpar.2009.09.015

Yabsley, M. J., and B. C. Shock. 2013. Natural history of zoonotic Babesia: Role of wildlife reservoirs. International Journal for Parasitology: Parasites and Wildlife 2: 18–31. doi: 10.1016/j.ijppaw.2012.11.003

Yunker, C. E., J. E. Keirans, C. M. Clifford, and E. R. Easton. 1986. Dermacentor ticks (Acari: Ixodidae) of the New World: A scanning electron microscope atlas. Proceedings of the Entomological Society of Washington 88: 609–627.

Supplemental Reading

Burger, T. D., R. Shao, M. B. Labruna, and S. C. Barker. 2014. Molecular phylogeny of soft ticks (Ixodida: Argasidae) inferred from mitochondrial genome and nuclear rRNA sequences. Ticks and Tick-Borne Diseases 5: 195–207. doi: 10.1016/j.ttbdis.2013.10.009

Cupp, E. W. 1991. Biology of ticks. Veterinary Clinics of North America: Small Animal Practice 21: 1–26. doi: 10.1016/s0195-5616(91)50001-2

Estrada-Peña, A., A. A. Guglielmone, and S. Nava. Worldwide host associations of the tick genus Ixodes suggest relationships based on environmental sharing rather than on co-phylogenetic events. Parasites and Vectors 16: 75. doi: 10.1186/s13071-022-05641-9

Guglielmone, A. A., S. Nava, and R. G. Robbins. 2023. Geographic distribution of the hard ticks (Acari: Ixodida: Ixodidae) of the world by countries and territories. Zootaxa 5251: 1–274. doi: 10.11646/zootaxa.5251.1.1

Guglielmone, A. A., S. Nava, and R. G. Robbins. 2021. Neotropical Hard Ticks (Acari: Ixodida: Ixodidae): A Critical Analysis of Their Taxonomy, Distribution, and Host Relationships. Springer, Cham, Switzerland. doi: 10.1007/978-3-030-72353-8

Guglielmone, A. A., T. N. Petney, and R. G. Robbins. 2020. Ixodidae (Acari: Ixodoidea): Descriptions and redescriptions of all known species from 1758 to December 31, 2019. Zootaxa 4871. doi: 10.11646/zootaxa.4871.1.1

Guglielmone, A. A., R. G. Robbins, D. A. Apanaskevich, T. N. Petney, et al. Comments on controversial tick (Acari: Ixodida) species names and species described or resurrected from 2003 to 2008. Experimental and Applied Acarology 48: 311–327. doi: 10.1007/s10493-009-9246-2

Leal, B., E. Zamora, A. Fuentes, D. B. Thomas, et al. 2020. Questing by tick larvae (Acari: Ixodidae): A review of the influences that affect off-host survival. Annals of the Entomological Society of America 113: 425–438. doi: 10.1093/aesa/saaa013

Nava, S., L. Beati, J. M. Venzal, L. A. Durden, et al. 2023. Description of two new species in the Ixodes ricinus complex from the New World (Acari: Ixodidae), and redescription of Ixodes affinis Neumann, 1899. Zootaxa 5361: 53–73. doi: 10.11646/zootaxa.5361.1.2

Nava, S., A. A. Guglielmone, and A. J. Mangold. 2009. An overview of systematics and evolution of ticks. Frontiers in Bioscience 1: 2,857–2,877. doi: 10.2741/3418

Vesco, U., N. Knap, M. B. Labruna, T. Avšič-Županc, et al. 2011. An integrated database on ticks and tick-borne zoonoses in the tropics and subtropics with special reference to developing and emerging countries. Experimental and Applied Acarology 54: 65–83. doi: 10.1007/s10493-010-9414-4