The family Ixodidae (the hard ticks or scale ticks) is characterized by the presence of a scutum on the dorsal surface. The scutum of the ixodid male covers the entire dorsal surface, while the scutum of the ixodid female, nymph, and larva covers only the anterior half of the dorsal surface. The ixodid capitulum arises from the anterior end of the body in each developmental stage.
Ixodid ticks of veterinary importance belong to the following genera: Amblyomma spp, Anomalohimalaya spp, Bothriocroton spp, Cosmiomma sp, Dermacentor spp, Haemaphysalis spp, Hyalomma spp, Ixodes spp, Margaropus spp, Nosomma sp, Rhipicentor spp, and Rhipicephalus spp.
Ixodid Parasitism in Ticks
Ixodidae number > 600 species, occupy many more habitats and niches than do argasids, and parasitize a greater number of vertebrates in a wider variety of environments. Most ixodid species have a three-host life cycle, others have a two-host cycle, and a few have a one-host cycle. Each ixodid postembryonic developmental stage (larva, nymph, adult) feeds only once but for a period of several days.
Males and females of most species that parasitize livestock mate on the host, although some mate off the host on the ground or in burrows. Males take less food than females but remain longer on the host and can mate with several females. During inactive seasons, few or no females are found feeding, even though males may remain attached to the hosts. Such males may contribute to transmission of pathogens to new susceptible animals by serial interhost transfer. Larval and nymphal population activity generally peaks during the “off seasons” of adults, although in some species there is overlap in the seasonal dynamics of immature ticks and adults.
The ixodid males, except those in the genus Ixodes, become sexually mature only after beginning to feed, after which they mate with a feeding female. Only after mating does the female become replete and proceed to develop eggs. She then detaches, drops from the host, and over a period of several days deposits a single batch of many eggs on or near the ground, usually in crevices or under stones, leaf litter, or debris. Depending on species and quantity of female nourishment, the egg batch usually numbers 1,000–4,000 but can be > 12,000. The female dies after oviposition.
Notably, ixodids (except one- and two-host species, which use vertebrate host animals as habitat for much of their life cycle) spend > 90% of their lifetime off the host, a fact of utmost importance in planning control measures. The several-day feeding process progresses slowly; the balloon shape characteristic of engorged larvae, nymphs, and females develops only during the final half day of feeding and is followed by detaching. The dropping time at certain hours of the day or night is governed by a circadian rhythm closely associated with the principal host's activity cycle.
It is also important, especially in understanding the epidemiology of tickborne pathogens, to know whether immature ticks of an ixodid species feed on the same host species as do the adults, or on smaller vertebrates. Where acceptable smaller-sized hosts are scarce, immature ticks of some ixodid species can feed on the same livestock hosts as adults; immature ticks of other species seldom or never do so.
The proximity of acceptable hosts, air temperature gradients, and atmospheric humidity during resting and questing periods (when they are seeking hosts on which to feed) are among the factors that regulate the development of each stage and, in females, oviposition.
Three-Host Ixodids
Most ixodids have a three-host cycle. Recently hatched larvae quest for a suitable host, usually from vegetation or at the mouth of host burrows, feed for several days, drop, and molt to nymphs, which repeat these activities and molt to adults.
Of the three-host species that parasitize livestock or dogs, a few have immature ticks and adults that parasitize the same kind of host; these often develop tremendous population densities.
The success of ixodid species that require smaller-size hosts for immature ticks depends on the availability of those hosts in the livestock browsing and grazing grounds.
The natural hazards inherent in the three-host cycle are compensated for by the benefits afforded adaptable tick species by animal husbandry practices. Only certain ixodids specific for herbivores have adapted to coexistence with livestock, and therein lies the answer to numerous livestock tick problems in Africa, where hosts for adults and immature ticks are abundant.
Two-Host Ixodids
Some ixodids, especially those that parasitize wandering mammals (and also birds, in certain cases) in inclement environments of the Old World, have developed a two-host cycle in which larvae and nymphs feed on one host, and adults on another. As in three-host species, hosts may be of different or the same species.
Two-host parasites of livestock thrive in both inclement and clement environments and are difficult to control. This is especially true of two-host species that feed in the ears and anal areas of livestock.
One-Host Ixodids
Among the most economically important ticks are several one-host species. These parasites evolved together with herbivores that wandered in extensive ranges in the tropics (Rhipicephalus spp, Dermacentor nitens, etc) or in temperate zones (D albipictus, Hyalomma scupense).
Larvae, nymphs, and adults feed on a single animal until the mated, replete females drop to the ground to oviposit.
Feeding Sites of Ticks
Each species has one or more favored feeding sites on the host, although in dense infestations, other areas of the host may be used. Some feed chiefly on the head, neck, shoulders, and escutcheon (the area below the vulva, extending toward the udder and thighs); others in the ears; others around the anus and under the tail; and some in the nasal passages. Other common feeding sites are the axillae, udder, male genitalia, and tail brush. Immature ticks and adults often have different preferred feeding sites.
Attachment of the large, irritating Amblyomma spp is regulated by a male-produced aggregation-attachment pheromone, which ensures that the ticks attach at sites least vulnerable to grooming.
Amblyomma spp of Ticks
More than half of the approximately 135 known Amblyomma species are endemic to the New World.
Amblyomma ticks are large, three-host parasites. They have eyes and long, robust mouthparts. They are more or less brightly ornamented and generally confined to the tropics and subtropics.
Adults and immature ticks of 37 species in this genus parasitize reptiles. Reptiles and ground-feeding birds can also host immature ticks of Amblyomma spp adapted to parasitizing mammals in the adult stage.
Their long mouthparts make Amblyomma ticks especially difficult to remove manually and frequently cause serious wounds that can become secondarily infected by bacteria or screwworms and other myiasis flies.
The African continent is home to 24 Amblyomma spp. Several African Amblyomma spp that infest livestock are vectors of Ehrlichia ruminantium, the rickettsial agent that causes heartwater, whereas New World Amblyomma spp carry agents of monocytic and granulocytic ehrlichioses as well as several Rickettsia spp, including R rickettsii, the agent of Rocky Mountain spotted fever (see A haebrumimage).
Courtesy of Dr. Raffaele Roncalli.
A americanum (the lone star tick) is abundant in the southern US from Texas and Missouri to the Atlantic Coast and ranges northward into Maine. Southward, its distribution extends into northern Mexico. Because of the changing climate, the geographic range of this species continues to expand.
The scutum is distinctive because of pale ornamentation in males and a conspicuous, silvery spot (“star”) near the posterior margin in females.
Larvae, nymphs, and adults are indiscriminate in host choice and parasitize a variety of livestock, pets, and wildlife as well as humans.
Activity in the US continues from early spring to late autumn.
Feeding sites on domestic and wild mammals are usually skin areas with sparse hair; wounds at these sites predispose livestock to attack by the screwworm fly Cochliomyia hominivorax.
A americanum is a vector of Francisella tularensis, the etiological agent of tularemia; Ehrlichia chaffeensis, which causes monocytic ehrlichiosis in humans; E ewingii, which causes granulocytic ehrlichiosis in dogs and humans; and Panola Mountain Ehrlichia, closely related to the agent of heartwater, which is pathogenic to goats and humans (at least). A americanum also transmits Rickettsia amblyommatis (formerly Candidatus R amblyommii), R parkeri, and R rickettsii; it carries endosymbiotic (presumably nonpathogenic) Borrelia lonestari and a Coxiella sp bacterium, both of which have been identified only by molecular methods but not isolated in culture.
A americanum may cause tick paralysis in humans and in dogs. In addition, A americanum is the vector of several tickborne viruses, including Bourbon virus (Orthomyxoviridae), Heartland virus (Phenuiviridae), and lone star virus (Bunyaviridae).
A aureolatum is an important vector of R rickettsii, the agent of Rocky Mountain spotted fever (Brazilian spotted fever in Brazil) in the rainforest region of eastern South America.
A aureolatum is present from Uruguay to Suriname, including eastern and southern Brazil, French Guiana, eastern Argentina, and Paraguay.
In natural settings, A aureolatum adults feed mainly on wild carnivores, while larvae and nymphs infest passerine birds and rodents. Domestic dogs are infested with adult A aureolatum in the forest and bring ticks home with them.
Six closely related tick species belonging to the A cajennense complex comprise the Cayenne ticks, which range from southern Texas to South America:
A mixtum: US to Ecuador
A cajennense: Amazon region of South America from Venezuela to Brazil
A patinoi: Cordillera of Colombia
A interandinum: inter-Andean valley of Peru
A sculptum: humid environs of southern Brazil, Bolivia, Paraguay, and northern Argentina
A tonelliae: dry areas of the Chaco region (central-northern Argentina to Bolivia and Paraguay)
Ticks of the A cajennense complex are indiscriminate in host choice; livestock and a large variety of avian and mammalian wildlife serve as hosts. Dense infestations on cattle and horses lead to anemia, weight loss, and production losses.
Humans are severely irritated by clusters of larvae (“seed ticks”) in wooded and high-grass areas. Most adults attach on the lower body surface, especially between the legs; some feed elsewhere on the body.
In general, activity of different life stages continues throughout the year. However, because A cajennense complex has been divided into six individual species, vertebrate host preferences, natural life cycles, and seasonal dynamics for each of the newly delimited species are yet to be described.
A cajennense complex ticks have been variably described as vectors of R parkeri and R rickettsii, as well as experimentally shown to transmit E ruminantium. Wad Medani virus (genus Orbivirus, family Reoviridae), an African virus transported to Caribbean islands by A variegatum-infested cattle from Senegal, has been isolated from A mixtum in Jamaica.
A maculatum (the Gulf Coast tick) is an important pest of livestock, particularly cattle, from South America to the southern US. Optimal habitats are warm areas with high rainfall, near seacoasts. However, in the US, A maculatum has expanded from the Gulf Coast to the Midwest and along the Atlantic seaboard from Florida to Virginia. The northward expansion is believed to be due to dispersal of immature ticks carried by migratory birds, as well as to climate change, which allows tick survival at higher latitudes.
Immature ticks usually parasitize birds and small mammals; adults parasitize deer, cattle, horses, sheep, pigs, and dogs. Adult feeding activity is chiefly in late summer and early autumn but may begin later after a dry summer. Most adults infest the ears, where the feeding wounds are initial sites of screwworm infestations. Adults feeding in clusters also cause much irritation to the upper parts of the neck of cattle and to the humps of Brahman cattle.
A maculatum is the primary vector of R parkeri, and in some tick populations, up to 50% of individual ticks may be infected with this pathogen. A maculatum is also the principal vector of the canine pathogen Hepatozoon americanum.
A imitator parasitizes livestock from Central America to southern Texas; it has been shown to transmit R rickettsii in Mexico. Occasional pests of livestock in tropical Mexico and South America are A neumanni (Argentina), A ovale and A parvum (Argentina to Mexico), A tigrinum (much of South America), and A tapirellum (Colombia to Mexico).
A ovale is a frequent and abundant parasite of roaming (unrestrained) dogs in rural areas from central Mexico to northeastern Argentina; however, occasional findings have been reported as far north as Iowa, in the US. Under natural conditions, A ovale adults parasitize wild carnivores, whereas rodents are preferred hosts for larval and nymphal stages. A ovale is an important vector of R parkeri (Atlantic rainforest Rickettsia) in Brazil.
A testudinarium inhabits Asian tropical wooded environments from Sri Lanka and India to Malaysia and Vietnam, Indonesia, Borneo, Philippines, Taiwan, and southern Japan. Adults are particularly abundant on wild and domestic pigs and also infest deer, cattle, other livestock, and humans. Immature ticks parasitize birds and small mammals as well as humans. In India and Sri Lanka, adult A integrum and A mudaliari also parasitize livestock, wild ungulates, and humans.
A hebraeum (the southern Africa bont tick) inhabits warm, moderately humid savannas of South Africa, Namibia, Botswana, Zimbabwe, Malawi, Mozambique, and Angola. Immature ticks feed on various small mammals, ground-feeding birds, and reptiles. Adults infest livestock, antelope, and other wildlife. Adults, attached chiefly to body areas with relatively little hair, cause serious wounds that become secondarily infected by bacteria and the screwworm Chrysomya bezziana. Like other African Amblyomma ticks (bont ticks) that parasitize livestock, A hebraeum is an important vector of Ehrlichia ruminantium and the principal vector of Rickettsia africae—the agent of African tick bite fever—in southern Africa.
A variegatum (the tropical African bont tick) is an easily visible, brightly colored parasite found throughout sub-Saharan savannas southward to the range of A hebraeum, and also in southern Arabia and several islands in the Indian and Atlantic oceans and the Caribbean. An eradication program is in progress in the Caribbean; St. Kitts, St. Lucia, Montserrat, Anguilla, Barbados, and Dominica qualified for "provisionally free" certification by 2002, although St. Kitts was reinfested in 2004.
Host preferences of A variegatum are similar to those of A hebraeum but also include camels. Tropical bont tick bites are severe. They may result in septic wounds and abscesses, inflammation of cows' teats, and considerable hide and skin damage. Adults feed chiefly during rainy seasons; immature ticks, during dry seasons. Most adults attach to the underside of the host body, on the genitalia, and under the tail.
A variegatum injuries to hosts and transmission of E ruminantium are similar to those of A hebraeum but also include the spread of acute bovine dermatophilosis. A variegatum is not considered to be an effective vector of Nairobi sheep disease virus but is a secondary vector of Crimean-Congo hemorrhagic fever virus. Dugbe virus has been isolated from A variegatum in six countries north of the equator; the Thogoto and Bhanja viruses are also associated with A variegatum in various areas north of the equator. Notably, yellow fever virus has been isolated from A variegatum collected from cattle in the Central African Republic and has been demonstrated to be transovarially transmitted to the progeny of infected females. Jos virus infects A variegatum from Ethiopia to Senegal and has been transported in this tick to Jamaica.
Five tick species are vectors of Ehrlichia ruminantium (heartwater) and Theileria mutans (benign African theileriosis):
A lepidum (the East African bont tick) inhabits xeric savanna environments from northern Tanzania to central Sudan.
A gemma (the gemlike bont tick) occurs in similar environments of Tanzania, Somalia, Kenya, and Ethiopia.
A small variety of the buffalo bont tick, A cohaerens, is abundant on cattle in Ethiopian highlands; however, from Zaire to Tanzania, the larger variety of A cohaerens parasitizes chiefly Cape buffalo.
A pomposum of humid highland forests in Angola, Zaire, Uganda, southern Sudan, Kenya, and Zimbabwe, is a tick of Cape buffalo and various other large mammals.
A astrion is found on livestock of West Africa and Zaire.
African Amblyomma spp parasitizing small ruminants include A hebraeum, A lepidum, A cohaerens, A gemma, A pomposum, and A variegatum.
In Central and South America, numerous Amblyomma spp parasitize livestock and dogs, often in large numbers. A ovale adults feed primarily on carnivores and A parvum on carnivores and armadillos.
A auricularium has been found on wild hosts of the families Myrmecophagidae and occasionally Didelphidae, Caviidae, Chinchillidae, Hydrochaeridae, Muridae, Canidae, Mustelidae, and Procyonidae. A auricularium transmits R rickettsii in Brazil.
A pseudoconcolor has been found occasionally on wild hosts of the family Didelphidae.
A naponense is common on peccaries, and A oblongoguttatum has been found on a variety of hosts in several South and Central American countries.
Capybaras are the main host for all stages of A dubitatum, although its geographical range is smaller than that of the principal host.
The South American tapir (Tapirus terrestris) seems to be the primary host for the adult stage of A latepunctatum, A scalpturatum, and A incisum.
A dissimile is a common parasite of reptiles and true toads of the genus Bufo, from Argentina northward to southern Mexico, the Caribbean islands, and southern Florida.
Dermacentor spp of Ticks
Of the 35 recognized Dermacentor spp, 19 inhabit temperate zones, and 13 are found exclusively in the Palearctic region. Among the tropical species, D nitens is of major veterinary importance, although other ticks may transmit zoonotic infections, and adults may be common on wildlife such as pigs, deer, and antelope. Immature ticks infest chiefly rodents and lagomorphs.
Dermacentor spp in cold areas and D nitens in tropical North and South America have specialized life cycles and seasonal dynamics of activity, each of which must be considered separately.
Except for D nitens, D albipictus, and D dissimilis, the Dermacentor life cycle is of the typical three-host pattern.
D nitens (the one-host tropical horse tick) is of considerable veterinary importance. It originally parasitized deer (Mazama spp) in the forests of northern South America. With the introduction of Equidae and other livestock into its habitat, it adapted to these animals. Spending its entire parasitic life deep in the hosts’ ears, D nitens was easily spread by human activities to other areas of the Americas, including Florida and Texas.
In addition to ear cavities, each active stage may infest nasal passages and the mane, ventral abdomen, and perianal area.
D nitens transmits Babesia caballi transovarially to successive generations and is important in the horse-racing industry. It also is an experimental vector of Anaplasma marginale to cattle.
Another American one-host species, D albipictus (the winter or moose tick) ranges from Canada and the northern US into the western US and Mexico (see D albipictusimage). A brownish form, sometimes called D nigrolineatus, is distributed from New Mexico to the southern and eastern US and may merit subspecies, if not full species, rank.
The larval-nymphal-adult feeding period for D albipictus on a single host (moose, deer, elk, or domestic cattle or horses) extends from autumn to spring.
Heavy infestation with D albipictus causes the often fatal "phantom moose disease” in which an animal is so irritated by ticks that it rubs off most of its hair, exposing bare skin.
D albipictus is a secondary vector of Colorado tick fever virus and an experimental vector of B caballi; it is a natural vector of A marginale in Oklahoma.
Courtesy of Dr. Sameeh M. Abutarbush.
In Mexico and Central America, D dissimilis parasitizes a variety of equine and ruminant hosts and may be a one-host tick on horses.
D andersoni (the Rocky Mountain wood tick) is found from Nebraska westward to the western mountains (Cascade Range and Sierra Nevada), in western Canada, and southward to northern New Mexico and Arizona.
D variabilis (the American dog tick) is found west of the Cascade Range and Sierra Nevada, along the Gulf Coast in Mexico, from Montana to Texas and east to the Atlantic in the US, and in southeastern Canada. An isolated population of D variabilis is also present along the West Coast, concentrated in California.
Both D andersoni and D variabilis ticks usually prefer brushy field habitat. Adults of both species parasitize livestock and wildlife, including deer, bison, and elk, but adult D variabilis prefer skunk, raccoon, puma, and domestic dogs, as well as some other hosts of intermediate size. Immature ticks feed on rodents and other small wild mammals.
Both D andersoni and D variabilis may cause tick paralysis in livestock, wildlife, and humans.
D andersoni and D variabilis are the primary vectors of R rickettsii, the agent of Rocky Mountain spotted fever. D andersoni is also the chief vector of Colorado tick fever virus and transmits Powassan virus, A marginale, A ovis, and the agents of tularemia and coxiellosis. D variabilis is an experimental vector of A marginale, B caballi, and B equi. In addition, sawgrass virus, Ehrlichia chaffeensis, and E ewingii have been occasionally detected in questing D variabilis adults.
A related, biologically similar species, D occidentalis, is restricted to the Pacific lowlands and foothills from Oregon to Baja California and is a natural vector of A marginale.
In western US and Mexico, D parumapertus, D hunteri, and D halli parasitize various hares and rabbits, mountain sheep, and peccaries, respectively. These ticks seldom make contact with livestock. D hunteri is an experimental vector of A marginale and A ovis. D parumapertus is a vector of a unique strain of Rickettsia parkeri in the western US. In Costa Rica and Panama, D latus infests tapirs.
In Eurasian steppes, forests, and mountains, D marginatus, D reticulatus, and D silvarum, collectively, are vectors of Rickettsia slovaca and R raoultii (the causative agents of tickborne lymphadenopathy), R sibirica (the agent of Siberian tick typhus), Babesia bovis, B caballi, B equi, B canis, Theileria ovis, and A ovis, together with the agents of tularemia and coxiellosis, and Russian spring-summer encephalitis. Brucella melitensis and Brucella abortus have been identified in progeny of D marginatus females collected from sheep and cattle, respectively, demonstrating the tick's ability for transovarial transmission of those pathogens.
D marginatus is found in forests, marshes, semideserts, and alpine zones from France to southwestern Siberia, Kazakhstan, Xinjiang (China), Iran, and northern Afghanistan. D reticulatus ranges from Ireland and Britain to northwestern Siberia and Xinjiang, China, in meadows, floodplains, and deciduous and deciduous-conifer forests. D silvarum ranges from central Siberia and northeastern China to Japan in marshes, meadows, shrubby and secondary forests, and farmlands in taiga forest areas.
Some males in populations of each of these three species remain attached to the host during winter. Adults and immature ticks may overwinter on the ground. The greatest adult activity is from early spring to summer with a lower peak in autumn. Larvae and nymphs are active from spring through autumn. The life cycle may be completed in 1 year or extended by one or more summer or winter diapauses to 2–4 years.
Approximately 12 other Dermacentor spp inhabit certain lowland, mountain steppe, and semidesert areas of temperate Asia. Their adults are commonly taken from camels, cattle, horses, sheep, and goats. In tropical Asia, the several species of the Dermacentor subgenus Indocentor are parasites of wild pigs; they also infest larger wildlife but seldom if ever feed on livestock.
Haemaphysalis spp of Ticks
Few of the recognized 167 species of Haemaphysalis parasitize livestock; however, those that do are economically important in Eurasia, Africa, Australia, and New Zealand.
Some haemaphysaline parasites of wild deer, antelope, and cattle have adapted to domestic cattle and, to a lesser extent, to sheep and goats. Others, originally specific for various wild sheep and goats, have adapted chiefly to the domestic breeds of these animals. A few African species that evolved together with carnivores now parasitize domestic dogs. Immature ticks of species that parasitize livestock generally feed on small vertebrates, but there are a few notable exceptions.
All Haemaphysalis spp have a three-host life cycle.
They are small (unfed adults < 4.5 mm long), brownish or reddish, and eyeless. Most have very short mouthparts.
Different species cause tick paralysis and are vectors of the agents that cause coxiellosis, tularemia, and brucellosis, and of other pathogens (eg, Theileria orientalis, T ovis, Babesia major, B motasi, B canis, Anaplasma mesaeterum).
H punctata (the red sheep tick) is widely distributed where sheep, goats, and cattle feed in certain open forests and shrubby pastures from southwestern Asia (Iran and the former Soviet Union) to much of Europe, including southern Scandinavia and Britain. H punctata usually does not appear in large numbers. Immature ticks infest birds, hedgehogs, rodents, and reptiles.
H punctata can cause tick paralysis. In addition to transmitting Anaplasma bovis, Brucella, Theileria, Babesia spp, and tularemia, different H punctata populations are infected by Russian spring-summer encephalitis virus, Tribec virus, Bhanja virus, and Crimean-Congo hemorrhagic fever virus.
H concinna is found in Central Europe, East and Southeast Asia, China, and Japan. It is found in humid scrubby forests as well as in meadows and peatlands but avoids dense forests.
H concinna can transmit tularemia; several Rickettsia spp, including mildly pathogenic R heilongjiangensis; and several encephalitis viruses.
H sulcata adults parasitize livestock (chiefly sheep and goats) from northwestern India and Turkmenistan to Arabia, Sinai, and southern Europe. H parva adults parasitize these hosts from southern Ukraine, Georgia, Azerbaijan, and the Near East to the Mediterranean area (but not Egypt). Immature H sulcata are especially common on lizards, but the range of hosts of larvae and nymphs of both species is similar to that of H punctata.
H longicornis (the Asian longhorned tick) is a serious pest of deer and livestock. It is endemic in Japan and eastern China, from where it has spread to the Russian Far East and Korea. It is an introduced, and now established, exotic species in Australia, New Zealand, several island nations in the Western Pacific Region, and the US. In the US, H longicornis is established in at least 10 eastern states, from New York and Connecticut to Tennessee and North Carolina.
In Japan and northeast Asia, there is a bisexual form (race) in southern areas and a parthenogenetic race in northern areas. The latter has been introduced into Australia, New Zealand, the Pacific Islands, and the US, where it preserves this unusual reproductive ability.
Originally a parasite of wild ungulates, H longicornis adapted to feeding on livestock in all life stages. The ability to reproduce parthenogenetically (without a male) allows a single fed female tick to create a large localized population. As such, the Asian longhorned tick frequently builds copious infestations on animals, causing great stress, decreased growth and production, and substantial blood loss that can lead to acute anemia and death. In addition to deer, livestock, and dogs, immature H longicornis ticks can parasitize medium-sized mammals and birds but are rarely found on rodents.
H longicornis is an important vector of human and animal disease agents. In China and Japan, it transmits both the severe fever with thrombocytopenia syndrome virus, which causes a human hemorrhagic fever, and Rickettsia japonica, the agent of Japanese spotted fever. H longicornis is the primary vector of Theileria orientalis and also transmits Babesia ovata, B gibsoni, and the agents of coxiellosis, Powassan encephalitis, and Russian spring-summer encephalitis. Larval feeding causes acute dermatitis in humans.
H inermis is found in lowlands from northern Iran to central and southeastern Europe to Italy, where it prefers deciduous and mixed forests as well as grasslands. It can cause tick paralysis. Other Eurasian haemaphysalines of livestock are H pospelovashtromae (mountains of southern former Soviet Union and Mongolia), H kopetdaghica (Caspian Sea area, mountains of former Soviet Union, and Iran), and H tibetensis, H xinjiangensis, and H moschisuga (China).
Of the several Haemaphysalis spp parasitizing livestock and dogs in southeast Asia, three are especially noteworthy:
H bispinosa ranges to Pakistan, Bangladesh, Nepal, Bhutan, Sri Lanka, and Malaysia, and transmits Babesia spp to cattle, sheep, and dogs.
H spinigera is the chief vector of Kyasanur Forest disease virus in humans in Karnataka, India.
H anomala ranges from the Nepal lowlands to Sri Lanka and the mountains of northwestern Thailand.
In temperate Asia, 18 other haemaphysalines parasitize livestock: 9 high in the Himalayas and outlying mountains, and 9 in northeastern Russia, Korea, and Japan. Yak and yak-cattle hybrids are among the livestock hosts of Himalayan haemaphysalines. Several Himalayan species appear to prefer sheep and goats.
H leachi (the yellow or African dog tick) is found in tropical and southern Africa. It parasitizes primarily wild and domestic carnivores and can transmit canine and feline babesiosis, Mediterranean spotted fever, coxiellosis, and Boutonneuse fever. Other haemaphysalines that infest livestock in highland forests or lowland, humid, secondary, or riparian forests in sub-Saharan Africa are H parmata (Ethiopia and Kenya, Central and West Africa, to Angola), H aciculifer (Ethiopia to Cameroon and Zimbabwe, introduced into South Africa), H rugosa (southern Sudan and Uganda to Ghana and Senegal), and H silacea (Zululand and eastern South Africa).
Hyalomma spp of Ticks
Hyalomma ticks are often the most abundant tick parasites of livestock, including camels, in warm, arid and semiarid, generally harsh lowland and middle-altitude biotopes, and those with long dry seasons, from central and southwest Asia to southern Europe and southern Africa. Of the 27 recognized Hyalomma spp, approximately 15 are important vectors of infectious agents to livestock and humans.
The three-host life cycle predominates in this genus; however, some species have either a one- or two-host cycle. Some three-host species can develop in one- or two-host cycles, a facultative ability unique to this ixodid genus. Hyalomma spp are mostly moderately large to large ticks with long mouthparts.
In the subgenus Hyalommasta, immature ticks of the single species H aegyptium parasitize tortoises, small wildlife, and livestock from Pakistan to both sides of the Mediterranean basin. Adults are specific for tortoises.
The subgenus Hyalommina is found on the Indian subcontinent and in Somalia. Each of the six species has a three-host cycle. Immature ticks parasitize small mammals, especially rodents. Adult host preferences among livestock reflect the wild gazelle, bovine, caprine, or ovine group with which each species evolved.
Two species infest chiefly cattle and the domestic buffalo:
H brevipunctata (India and Pakistan)
H kumari (India, Pakistan, Afghanistan, northwestern Iran, and Tadzhikistan)
Three usually parasitize sheep and goats:
H hussaini (India, Pakistan, Burma)
H rhipicephaloides (Dead Sea and Red Sea areas)
H arabica (Yemen and Saudi Arabia)
H punt (Somalia and Ethiopia) feeds on antelope, camels, cattle, sheep, and goats.
The subgenus Hyalomma contains ticks of veterinary and public health importance that affect cattle, sheep, goats, horses, camels, dromedaries, dogs, cats, and humans.
The topmost among these is the two-host H anatolicum anatolicum, which ranks high among the world’s most damaging ticks and has been widely distributed by camels, cattle, and horses in steppe and semidesert environments from central Asia to Bangladesh, the Middle and Near East, Arabia, southeastern Europe, and Africa north of the equator. Immature ticks and adults generally infest the same kinds of hosts. Nymphs and unfed adults spend the dry season and winter in crevices in stone walls, stables, and weedy or fallow fields. When immature ticks infest smaller mammals, birds, or reptiles, the life cycle type is three-host.
In addition to substantially weakening affected animals—causing weight loss, lower fertility, and decreased milk production—H anatolicum anatolicum transmits Theileria annulata, Babesia equi, B caballi, Anaplasma marginale, Trypanosoma theileri, and at least five arboviruses. It is an important vector of Crimean-Congo hemorrhagic fever virus to humans.
Immature ticks of H anatolicum excavatum (a three-host parasite) chiefly infest burrowing rodents in somewhat different biotopes in the same environments as H anatolicum anatolicum. Adults of both species may infest the same animal. Distribution of H excavatum is somewhat more limited than that of H anatolicum; however, winter population densities of H excavatum are often greater than those of H anatolicum. A closely related species, H lusitanicum, replaces H anatolicum from central Italy to Portugal, Morocco, and the Canary Islands; it is associated with equine and bovine babesiosis. In addition to livestock, deer and rabbits serve as hosts.
The H marginatum complex consists of four species, each apparently invariably two-host. Adults parasitize livestock and wild herbivores. Immature ticks primarily parasitize birds. Rodents are rarely, if ever, parasitized. Hares and hedgehogs are secondary hosts. This group includes H marginatum (Caspian area of Iran and the former Soviet Union to Portugal and northwestern Africa), H rufipes (south of the Sahara to South Africa, also Nile Valley and southern Arabia), H turanicum (Pakistan, Iran, southern former Soviet Union, Arabia, parts of northeastern Africa—introduced with sheep from Iran to southern Africa), and H isaaci (Sri Lanka to southern Nepal, Pakistan, northern Afghanistan).
Migratory birds are known to introduce these ticks to regions outside of their normal range. Adult H marginatum and H rufipes have been found on large mammals in different parts of Germany and Dorset, England, respectively, indicating successful molting and overwintering of Hyalomma nymphs in Central and Western Europe. Ticks belonging to the H marginatum complex are major vectors of Crimean-Congo hemorrhagic fever virus. They also transmit Rickettsia aeschlimannii and several Babesia, Anaplasma, Theileria, and Trypanosoma spp that infect wildlife, livestock, and humans. H truncatum can cause paralysis in livestock, pets, and humans.
The H asiaticum complex includes three species with three-host life cycles and inhabits deserts, semideserts, and steppes from southwestern China, Mongolia, and the southern former Soviet Union into the Middle East as far as Iraq. Rodents are the main hosts of immature ticks; hares also may be infested. Adults parasitize livestock, particularly camels. From east to west, the species H kozlovi, H asiaticum, and H caucasicum are of veterinary and medical importance. H asiaticum transmits bovine tropical theileriosis (Theileria annulata) and human rickettsiosis (Rickettsia mongolotimonae).
Three additional three-host Hyalomma spp that parasitize camels and other livestock are H dromedarii (India to Africa north of the equator), H schulzei (eastern Iran to Arabia and northern Egypt), and H franchinii (Syria to Tunisia). Immature ticks parasitize rodents and other small mammals, birds, and reptiles; H dromedarii immature ticks also infest livestock. Interestingly, H dromedarii can also exhibit one-host and two-host life cycles. H dromedarii is of veterinary and medical importance as a vector of bovine tropical theileriosis.
H impeltatum ranges from Iran and Arabia to northern Tanzania and Chad. Adults parasitize medium-sized to large mammals, including livestock, horses, and dogs; immature ticks feed on rodents and other small mammals, birds, and reptiles.
H scupense (syn H detritum) is a two-host or one-host species; both adults and immature ticks parasitize livestock and other ungulates. Its biotopes are humid areas in steppes, deserts, and semideserts from southern China, Mongolia, and Nepalese lowlands to southern Europe and northern Africa. In Central Asia and southeastern Europe, H scupense is a one-host tick overwintering on the host, which often suffers greatly from the long feeding period of numerous larvae (late autumn), nymphs (winter), and adults (spring). H scupense is a vector of Theileria annulata, T equi, and Babesia equi.
African Hyalomma spp infesting livestock and wildlife include the following:
H excavatum (Tunisia)
H albiparmatum (southern Kenya, northern Tanzania)
H impressum (western Sudan and West Africa)
H marginatum (Algeria, Ivory Coast)
H nitidum (Central African Republic and West Africa)
H rufipes (Kenya, Mali, Sudan, South Africa, Zimbabwe)
H scupense (Algeria, Ivory Coast)
H truncatum (southeastern Egypt to southern Africa)
H truncatum, which causes bovine sweating sickness and lameness as well as human and ovine tick paralysis, is a vector of Crimean-Congo hemorrhagic fever virus, Coxiella burnetii (Q fever), Rickettsia aeschlimannii, and Rickettsia mongolotimonae.
Ixodes spp of Ticks
Ixodes, the largest genus of the family Ixodidae, contains approximately 245 species and is highly specialized, both structurally and biologically. So far as is known, all Ixodes spp have a three-host life cycle. Almost all inhabit temperate or tropical forest zones or wooded or shrubby grasslands; fewer are adapted to humid areas in semideserts or to Arctic or sub-Antarctic nesting colonies of marine birds.
Hosts are a wide variety of birds and mammals and a few reptiles. Most Ixodes species parasitize burrowing hosts or those that return regularly to caves, dens, or terrestrial or arboreal nesting colonies. The few Ixodes spp that parasitize wandering artiodactyls or perissodactyls are exceptionally adaptable; they also parasitize livestock and are important pests or vectors of agents that infect livestock and humans.
The I ricinus group of Eurasia, northwestern Africa, and North and South America is especially important as primary vectors of the agents of Lyme disease, anaplasmosis, babesiosis, and viral encephalitis throughout the Northern Hemisphere. I ricinus, the so-called sheep tick and prototype of this group, inhabits relatively humid, cool, shrubby and wooded pastures, gardens, windbreaks, floodplains, and forest through much of Europe to the Caspian Sea and northern Iran. Its life cycle is 2–4 years, depending on environmental temperature.
I ricinus larvae feed on small reptiles, birds, and mammals. Nymphs feed on small and medium-sized vertebrates, and adults feed chiefly on herbivores and livestock. All stages, especially nymphs and adults, parasitize humans. Male I ricinus take little or no food and can mate either on or off the host. Unfed adults often mate while on vegetation. Adult activity peaks in spring; in some populations, there is a lower peak of adult activity in the autumn. Among arboviral diseases transmitted by I ricinus are louping ill, tickborne encephalitis, and Crimean-Congo hemorrhagic fever. Other agents transmitted to livestock are Coxiella burnetii, Anaplasma marginale, Babesia divergens, and A phagocytophilum, various strains of which cause bovine, ovine, and human granulocytic anaplasmosis.
In drier, warmer, eastern Mediterranean biotopes, I ricinus is replaced by I gibbosus, which completes its life cycle in 1 year. I inopinatus has been found in Spain, Portugal, Morocco, Tunisia, Romania, and Germany. It may have been historically confused with and erroneously reported as I ricinus in parts of Spain, Portugal, and northern Africa. In southern Germany, I inopinatus and I ricinus can occur sympatrically and even on the same hosts (sheep and foxes). There are no data regarding the life cycle of I inopinatus or its seasonal activity, range of vertebrate hosts affected, or potential role as a vector of pathogens.
I persulcatus (the taiga tick) is closely related to I ricinus and has similar host preferences. It ranges from the central and eastern mountains of Europe, through the lowland forests from the Baltic Sea and Karelia, eastward through the Siberian taiga to the seas of Japan and Okhotsk and the northern islands of Japan. The life cycle can be completed in 3–4 years but can last up to 7 years in regions with a short summer season.
I persulcatus is one of the main vectors of Russian spring-summer encephalitis virus and Borrelia burgdorferi. In addition, it transmits Babesia spp, Ehrlichia muris, and the agents of human and ovine anaplasmoses and tularemia.
Other Asian representatives of the I ricinus group are I sinensis of China; I kashmiricus of mountainous northern India, Pakistan, and Kyrgyzstan; I pavlovskyi of the southern Siberian mountains of Russia; and I kazakstani of mountain taiga and deciduous forest in Kazakhstan, Kyrgyzstan, and Turkmenistan.
In the Americas, representatives of the I ricinus group include I scapularis, I pacificus, I affinis, I jellisoni, I minor, and I muris.
I scapularis (the blacklegged tick) is distributed throughout the eastern and north central US and southern Canada (see I scapularisimage). It is a vector of B burgdorferi, the agent of Lyme disease, and A phagocytophilum, which causes granulocytic anaplasmosis in horses and dogs as well as anaplasmosis in humans. It also transmits Babesia microti, the agent of human babesiosis in coastal areas from Rhode Island to Virginia, and Ehrlichia muris subsp eauclairensis, which causes granulocytic ehrlichiosis in rodents and in humans in the midwestern US.
The chief hosts of adult I scapularis are deer; livestock seldom graze in the wooded zones inhabited by this tick. Immature blacklegged ticks feed on a wide range of vertebrate hosts in April to July (nymphs) and June to August (larvae).
Courtesy of Dr. Steve J. Upton.
Adults of I pacificus parasitize livestock from Baja California to British Columbia and in inland pockets of Idaho, Nevada, and Oregon. I pacificus and I neotomae transmit the agents of Lyme disease, tularemia, and a rickettsia of the Rocky Mountain spotted fever group; I pacificus also transmits A phagocytophilum. I pacificus bites cause slowly healing ulcers.
A related species, I affinis, ranges from South Carolina and Florida to Argentina. It is recorded chiefly from wildlife and has not been shown to be a vector. It is undergoing a northward range expansion, becoming established in the coastal plains of North Carolina and Virginia. Adults are active during the hot summer months. I affinis is recorded chiefly from wildlife but can infest domestic dogs. It is known to be a competent vector for the agent of Lyme disease.
In Africa, only four Ixodes spp have adapted to livestock, of which I rubicundus (the South African paralysis tick) is the most important.
I rubicundus is predominately found in humid hill and mountain karoo vegetation in South Africa. Its salivary toxins cause a flaccid tetraplegia in livestock, humans, dogs, and jackals. Immature ticks parasitize the rock hare, other hares, and elephant shrews. The life cycle of I rubicundus is approximately 2 years.
I rubicundus can often be found along the lower line of the neck, chest, and belly. The active period for adult ticks usually begins in late summer, reaches peak levels in autumn and early winter (April/May), and declines thereafter.
Cases of paralysis due to I rubicundus commonly begin in February and reach a peak in April and May.
Other parasites of livestock in African highlands are I drakenbergensis (Natal), I lewisi (Kenya), and I cavipalpus (southern Sudan to Zimbabwe and Angola).
I holocyclus (the Australian paralysis tick) is considered the most medically important of the Australian tick fauna. Although most cases of tick bite are uneventful, some can result in life-threatening illnesses, including paralysis, tick typhus, and severe allergic reactions. The species is found throughout the year in a variety of habitats, particularly wet sclerophyll forests and temperate rainforest areas, across the humid coastal regions of eastern Australia.
Adult I holocyclus ticks are more abundant in the spring and early summer, larvae in mid- to late summer, and nymphs during winter.
Natural hosts for I holocyclus include bandicoots, kangaroos, possums, birds, and sometimes even reptiles; however, I holocyclus regularly attaches to domestic animals, including dogs, cats, cattle, and horses, and occasionally humans.
I holocyclus injects a neurotoxin that causes progressive motor paralysis, respiratory depression, and death in animals with no immunity to the toxin.
Most cases of tick paralysis seen by veterinarians are in dogs and cats; however, other species can be affected. The condition has been recorded in sheep, cattle, goats, llamas, and Muscovy ducks. Fatal cases have occurred in humans. In larger species, the younger and smaller animals are likely to be affected.
Rhipicephalus spp of Ticks
Approximately 60 of the 84 described rhipicephalid species are found in sub-Saharan Africa. The other rhipicephalid species have their origins in Eurasia and northern Africa, with Rhipicephalus (subgen Rhipicephalus) sanguineus and R (subgen Boophilus) microplus being spread by human activities into Asia, Australia, and the Americas. Adults of most species parasitize wild and domestic artiodactyls, perissodactyls, or carnivores. Immature ticks feed mostly on smaller mammals; however, of those that parasitize rodents or hyraxes, and of those that parasitize artiodactyls, a few feed on the same host as the adults.
The rhipicephalid life cycle is typically three-host. However, several ticks in the Rhipicephalus subgenus have a two-host cycle: R bursa, in the Mediterranean climatic zone (long, warm summer with low rainfall), and R evertsi and R glabroscutatum, in sub-Saharan Africa with long dry seasons. In contrast, each of the five species in subgenus Boophilus has a one-host life cycle that may be completed in 3–4 weeks.
A number of Rhipicephalus spp have long been difficult to identify or have been incorrectly identified. Contemporary understanding of tick phylogeny, taxonomy, and nomenclature is based on molecular analyses.
Subgenus Boophilus
Formerly a separate genus, Boophilus has been included as a subgenus of Rhipicephalus; however, the morphology of boophilid ticks is different from that of nominotypical Rhipicephalus subgenus ticks.
Each of the five Rhipicephalus spp in the subgenus Boophilus has a one-host life cycle that may be completed in 3–4 weeks and results in a heavy tick burden. Under these conditions, acaricide resistance becomes a major problem in control efforts. Zebu cattle, which have served for centuries as hosts of R microplus in the Indian region, have developed resistance to feeding by large numbers of ticks, and both purebred and crossbred Zebu cattle are used in integrated control programs.
R microplus, considered the world’s most important tick parasite of livestock, hasbeen introduced from the bovid- and cervid-inhabited forests of the Indian region to many areas of tropical and subtropical Asia, northeastern Australia, Madagascar, the coastal lowlands of southeastern Africa to the equator, and much of South and Central America, Mexico, and the Caribbean.
R microplus and R annulatus were eradicated from the US after a long, costly control program. Continuous surveillance is maintained to prevent their reintroduction.
R annulatus of the southern former Soviet Union, the Middle East, and the Mediterranean area was introduced with livestock of the early Spanish colonialists into northeastern Mexico but has not spread into Central America. In Africa, south of the Sahara and north of the equator, cattle movements probably account for the many R annulatus populations.
R decoloratus, which ranges from southern Africa to the Sahara, is being replaced in the southeastern part of this area by R microplus.
In more humid West African zones, R annulatus mixes with, or is totally replaced by, R geigyi. Scattered R geigyi populations are found as far east as southern and central Sudan.
The only boophilid tick restricted to sheep and goats (and occasionally horses) is R kohlsi of Syria, Iraq, Israel, Jordan, western Saudi Arabia, and Yemen.
R microplus and R annulatus are major vectors of Babesia bigemina, B bovis, and Anaplasma marginale. R microplus has been demonstrated experimentally to serve as a competent vector of B equi and has been collected from the nasal passages of equids in Panama.
R decoloratus is an efficient vector of B bigemina and A marginale but does not transmit B bovis or B equi.
Subgenus Rhipicephalus
Subgenus Rhipicephalus is the nominotypical subgenus of the genus Rhipicephalus.
Tropical Asia is the home of five species in the Rhipicephalus subgenus; adults of two species parasitize domestic animals:
R haemaphysaloides infests all types of livestock, as well as wild antelope, deer, carnivores, and hares in continental southeast Asia (and Taiwan and the Philippines) westward to India, Sri Lanka, Nepal, Pakistan, and western Afghanistan.
R pilans infests livestock and wildlife in Indonesia and Borneo. Immature ticks of both species feed chiefly on rodents, but also on shrews, hares, and smaller carnivores.
In Africa, 26 Rhipicephalus spp are recorded.
From central Europe to Kazakhstan, R rossicus, R schulzei, and Rpumilio are of medical and veterinary importance.
In southwestern Europe, R pusillus infests dogs as well as European rabbits, foxes, and wild pigs.
R turanicus, as presently recognized, ranges from China, India, and Turkmenistan into southern Europe, and Africa as far south as South Africa. A member of the taxonomically difficult R sanguineus group, “R turanicus” and its various populations, which may represent separate species, requires further studies of its abilities as a vector of animal and human pathogens.
An easily recognized two-host species, R bursa, ranges from the western Mediterranean area of Europe to Iran and Kazakhstan. Adults and immature ticks parasitize livestock, hares, deer, wild sheep and goats, humans, and, infrequently, dogs. R bursa causes ovine paralysis and transmits Crimean-Congo hemorrhagic fever virus and other viruses to humans, as well as numerous microbial diseases of livestock, such as various species of Babesia, Anaplasma, and Theileria (notably Theileria parva, the agent of East Coast fever, often fatal for cattle), Ehrlichia (syn Cowdria) ruminantium (the agent of heartwater), and Trypanosoma vivax (an agent of sleeping sickness).
The best known rhipicephalids, cumulatively known as R sanguineus sensu lato (the brown dog ticks), include at least two morphologically similar but molecularly, biologically, and geographically distinct species.
R sanguineus sensu stricto (the temperate brown dog tick) is present throughout most of Europe as well as in temperate regions of the New World (Argentina, southern Brazil, Chile, Uruguay, the US, and Canada).
Conversely, R linnaei (the tropical brown dog tick) is found circumglobally in tropical areas with annual mean temperature between 20°C and 30°C (68–86°F), including Africa, tropical Asia, Australia, Oceania, and from the US-Mexico border region to northern Brazil in the Americas.
Sympatric populations of the two species are reported in Chile and California. The taxonomic status of other potential lineages of brown dog ticks has not been ascertained. The "southeastern Europe" lineage of the brown dog ticks has been identified as Rhipicephalusrutilus, which is present in Israel and Egypt. Another member of the R sanguineus sensu lato complex, R hibericus, is present in the Iberian Peninsula (Spain, Portugal, south of France), where its range overlaps with those of R pusillus, R sanguineus sensu stricto, and R rutilus.
Whereas R sanguineus sensu stricto feeds preferentially on wild and domestic canines in all life stages, tropical brown dog ticks are known to parasitize wild and domestic carnivores, sheep, goats, camels, other livestock, and various wild mammals, especially hares and hedgehogs. Immature ticks of R linnaei in nature feed on small mammals. However, in urban situations everywhere, dogs are primary hosts of both immature ticks and adults. Humans are attacked infrequently, more often in situations where children play and sleep in close contact with heavily infested dogs. In heavily infested houses and kennels, adult and immature brown dog ticks are frequently observed climbing walls and emerging from floor-level cracks and crevices.
Brown dog ticks have been described as vectors of Anaplasma platys, Babesia canis, Ehrlichia canis, Rickettsia rickettsii, Rickettsia rhipicephali, Rickettsia conorii, Crimean-Congo hemorrhagic fever virus, and Thogoto virus. However, the two species of the R sanguineus sensu lato group may also differ in vector competence because only the "tropical lineage" can maintain and transmit E canis, the agent of canine ehrlichiosis. Certain American populations of R sanguineus have become resistant to insecticides. The hymenopteran (chalcid) parasite of ticks, Ixodiphagus hookeri (formerly Hunterellus hookeri), frequently infests nymphal R sanguineus in East Africa.
R appendiculatus (the brown ear tick) is a major pest in cool, shaded, woody, and shrubby savannas from southern Sudan and eastern Zaire to Kenya and South Africa. Adults and immature ticks feed in the ears of cattle, other livestock, and antelope, but also on other areas when the infestation is massive. Immature ticks may infest small antelope and carnivores, and occasionally rodents. Engorged females lay as many as 5,000 eggs. The life cycle lasts 3–9 months. Seasonal activity is closely associated with temperature and rain periods. As many as three generations a year can follow in regions with two rainy seasons.
R appendiculatus is the major vector of the Theileria parva group of diseases (East Coast fever, Corridor disease, Zimbabwe malignant theileriosis) and Nairobi sheep disease virus, and is also a vector of T taurotragi, Ehrlichia bovis, Rickettsia conorii, and Thogoto virus. Heavy infestations on susceptible Bos taurus cattle cause a sometimes fatal toxemia, loss of resistance to various infections, and severe damage to the host’s ears.
The closely related R zambeziensis, with similar host preferences, is found in drier lowland savannas in Tanzania, Zimbabwe, Zambia, Botswana, and parts of South Africa; it also is a vector of East Coast fever. Other species closely related to R appendiculatus include R nitensin the former Cape Province of South Africa and R duttoni in Angola and Zaire.
The ivory-ornamented R pulchellus, a parasite of zebras, also infests livestock and game animals in savannas, moist broadleaf forests, and dry shrublands east of the Rift Valley from southern Ethiopia to Somalia and northeastern Tanzania. Adults and immature ticks generally infest the same host; however, immature ticks also feed on hares, and larvae (seed ticks) are notoriously annoying pests of humans. R pulchellus feeds in the ears and on the lower abdomen, chiefly during wet seasons. R pulchellus is a vector of Babesia equi (among zebras), Theileria spp, Trypanosoma theileri, Rickettsia conorii, several Bunyaviridae (Crimean-Congo hemorrhagic fever virus; Nairobi sheep disease; and Kajiado, Kismayo, and Dugbe viruses), and Barur virus.
The two-host African rhipicephalids are R glabroscutatum and two subspecies of Revertsi.
R evertsi evertsi, a large, beady-eyed, red-legged tick, is a parasite of the East African zebra and parasitizes all types of herbivorous wildlife and livestock (but seldom pigs). Immature ticks and adults infest the same hosts; immature ticks are also recorded from birds.
R evertsi evertsi ranges from South Africa through eastern Africa east of the Nile to southern Sudan and is established in the mountains of Yemen. Scattered foci, introduced by domestic animals, are found west of the Nile.
On bovids and equids, immature R evertsi evertsi ticks feed in the external ear canal; adults feed mostly around the anus and under the tail but also in the axillae and groin and on the sternum. Large numbers on a single host are common on Equidae and are difficult to control because of tick concentrations in difficult-to-reach feeding sites.
Adult females lay as many as 7,000 eggs. The life cycle takes 36 months to complete, depending on weather conditions.
R evertsi evertsi is a vector of Babesia caballi, B equi, Theileria equi, T separate, and T parva (secondary vector). It has also been reported to transmit Anaplasma marginale, Borrelia theileri, Rickettsia conorii, and Kerai, Wad Medani, and Thogoto viruses.
The banded-legged (Hyalomma-like) western subspecies R evertsi mimeticus, found from western Botswana to Namibia, Angola, and Zaire, is like the nominate subspecies in host preferences, feeding sites, and life cycle.
The tiny (< 3 mm in length) R glabroscutatum has become a common pest of sheep, goats, and other livestock in the arid, small-shrub savanna of Eastern Cape, South Africa. Horses, kudu, and other small antelope are also infested. The few records of immature ticks are from hares. On livestock, all life stages feed around the hooves and below the fetlocks of their hosts. Secondary bacterial infection of attachment sites can lead to foot abscesses and lameness, particularly in Angora goats.
The R pravus group, which is under taxonomic study, consists of four or more species in which the adults feed on livestock and herbivorous wildlife (including hares); immature ticks feed on elephant shrews (insectivores), hares, and other small mammals. R pravus, a brown, convex-eyed tick, is found in shrubby and wooded savannas in east Africa from Ethiopia and Somalia to Tanzania. It is infected by Kadam virus. The closely related R occulatus, a parasite of hares, and another related, unnamed parasite of livestock are found in southern Africa.
The difficult-to-classify R punctatus group of parasites of livestock and wild artiodactyls consists of R punctatus (Angola, Mozambique, Tanzania), R kochi (syn neavei) (Botswana to Kenya and Zaire), and an unnamed species from Zimbabwe and South Africa.
The R capensis group is also under study. Originally parasites of the Cape buffalo, these species now parasitize livestock and wildlife across Africa:
Namibia and South Africa: R capensis and R gertrudae
East Africa: R compositus and R longus
West Africa to southwestern Sudan: R pseudolongus
Above 1,800 m (5,900 feet) altitude in East African forest and shrub zones, R hurti and R jeanelli infest livestock and Cape buffalo and other large game animals. R hurti also inhabits mountains in Zaire. Both species feed chiefly in the hosts’ ears; R jeanelli also feeds in the tailbrush.
R simus, the prototype of the R simus group and long considered a well-established species, is divided into several species. R simus sensu stricto is found through central and southern Africa, roughly south of latitude 8°S, where it is a competent experimental vector of Anaplasma marginale and A centrale. In eastern and northern Africa, R simus is replaced by a less punctate species, R praetextatus, which ranges from central Tanzania to Egypt.
Adults of both R simus and R praetextatus parasitize livestock, dogs, wild carnivores, large and medium-sized game animals, and humans. Occurrence and densities on livestock are inexplicably erratic. Immature stages feed on the common burrowing rodents in savannas.
Both R simus and R praetextatus cause tick paralysis in humans and transmit Rickettsia norii and Coxiella burnetii. In Kenya, R praetextatus is a vector of Thogoto virus and may be a secondary vector of Nairobi sheep disease virus. West of the Nile, these species are replaced by R senegalensis and R muhsamae.
Much literature regarding R tricuspis (Tanzania to South Africa) and R lunulatus (West Africa to Ethiopia and Tanzania) has been incorrect due to misidentification. The chief feeding sites on both livestock and wildlife are the legs and tailbrush; however, other parts of the host are also feeding sites. R lunulatus is suspected of transmitting Babesia trautmanni, the cause of porcine piroplasmosis. In West Africa, ticks of this group have been associated with tick paralysis in sheep and lambs.
Related species are R camicasi (ranging from Sudan to Kenya to Somalia), R bergeoni (Ethiopia and Sudan), R guilhoni (Senegal and Mauritania to Sudan and Ethiopia), R moucheti (West Africa from Guinea to northern Cameron), and two widely distributed “forms” of R sulcatus, which are under study.
Two quite distinctive species often confused with R appendiculatus are R supertritus (Natal to southern Sudan) and R muehlensi (Kenya and southern Sudan to Central Africa). Adults of both species parasitize cattle, Cape buffalo, antelope, and big game animals; R supertritus is also found on carnivores.
Other Ixodid Species of Ticks
Anomalohimalaya spp of Ticks
The three Anomalohimalaya spp are found in mountains of Central Asia—Pamir, Tian Shan, Tibet, and the Himalayas. All stages of these three-host ticks parasitize rodents, shrews, and, less frequently, hares.
Bothriocroton spp of Ticks
The genus Bothriocroton includes seven species of ticks indigenous to Australia and Papua New Guinea (B oudemansi). Bothriocroton spp resemble Amblyomma spp except Bothriocroton have no eyes.
In this group, B auruginans is a parasite of wombats; B concolor and B oudemansi are ectoparasites of echidnas in Australia and Papua New Guinea, respectively. The other four species in this genus parasitize reptiles almost exclusively.
B hydrosauri (the blue-tongued lizard tick) is the reservoir of Rickettsia honei on Flinders Island, Australia.
Cosmiomma sp of Ticks
The genus Cosmiomma contains a single species, C hippopotamensis, which is found in Zambezian grasslands of southwestern and eastern Africa. It feeds primarily on hippopotami, white and black rhinoceroses, and, less frequently, on antelopes.
Margaropus spp of Ticks
Ticks of the genus Margaropus resemble Rhipicephalus ticks but do not have festoons or ornamentations. They are characterized by greatly enlarged posterior legs and a prolonged median plate. The three highly specialized beady-legged, one-host Margaropus spp are restricted to limited areas of Africa.
M reidi and M wileyi are recorded from giraffes in the Sudan and in Kenya and Tanzania, respectively. M wileyi is also known to parasitize zebras and gnu.
M winthemi, a winter-feeding parasite of zebras, horses, and, less often, other livestock and antelope, is confined to mountains of South Africa and may contribute to loss of condition during winter.
Nosomma sp of Ticks
The genus Nosomma contains a single species, N monstrosum. Adults particularly parasitize wild and domestic buffalo, and also humans, livestock, and wildlife, through much of India, the Nepalese lowlands, Bangladesh, Thailand, and Laos. Immature ticks parasitize chiefly murid rodents.
Rhipicentor spp of Ticks
The genus Rhipicentor is composed of two species, R bicornis and R nuttalli, which are found only in Africa south of the Sahara.
R bicornis feeds on goats, cattle, horses, dogs, and carnivores in southern and central Africa. R nuttalli has a widespread distribution in South Africa. Immature stages feed on elephant shrews. Adults' preferred hosts are domestic dogs, leopards, and South African hedgehogs.
The life cycle of these ticks probably takes a year to complete in the field.
For More Information
Guglielmone AA, Robbins RG, Apanaskevich DA, Petney TN, Estrada-Peña A, Horak IG. The Hard Ticks of the World (Acari: Ixodida: Ixodidae), Springer Dordrecht; 2014.
Guglielmone AA, Nava S, Robbins RG. Geographic distribution of the hard ticks (Acari: Ixodida: Ixodidae) of the world by countries and territories. Zootaxa. 5251(1):1-274.
Walker AR, Bouattour A, Camicas JL et al. Ticks of Domestic Animals in Africa: A Guide to Identification of Species. University of Edinburgh; 2003.
Barker SC, Walker AR. Ticks of Australia; the species that infest domestic animals and humans. Zootaxa. 2014;3816(1):1-144.
Estrada-Peña A, Mihalca AD, Petney TN, eds. Ticks of Europe and North Africa: A Guide to Species Identification. Springer; 2017.
