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Hyalomma spp

By

Michael L. Levin

, PhD, Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention

Last full review/revision Aug 2020 | Content last modified Sep 2020

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 people. The three-host life cycle predominates in this genus, but 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, immatures of the single species, H aegyptium, parasitize tortoises and 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. Immatures 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) and 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), and 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 people. 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. Immatures and adults generally infest the same kinds of hosts. Nymphs and unfed adults spend the dry and winter season in crevices in stone walls, stables, and weedy or fallow fields. When immatures infest smaller mammals, birds, or reptiles, the life cycle type is three-host.

In addition to significantly weakening affected animals, causing weight loss, reduced 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 a significant vector of Crimean-Congo hemorrhagic fever virus to people.

Immatures of H excavatum (a three-host parasite) infest chiefly burrowing rodents in somewhat different biotopes in the same environments as H anatolicum. Adults of both species may infest the same animal. Distribution of H excavatum is somewhat more limited than that of H anatolicum , but its winter season population densities are often greater. 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. Immatures 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 former USSR 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 USSR, Arabia, parts of northeastern Africa—introduced with sheep from Iran to Karoo), 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. Recently, 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 the Crimean-Congo hemorrhagic fever virus. They also transmit Rickettsia aeschlimannii and several Babesia, Anaplasma, Theileria, and Trypanosoma spp that infect wildlife, livestock, and people. H truncatum can cause paralysis in livestock, pets, and people.

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 USSR into the Middle East as far as Iraq. Rodents are the main hosts of immatures; hares also may be infested. Adults parasitize livestock, particularly camels. The species from east to west, 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). Immatures parasitize rodents and other small mammals, birds, and reptiles; those of H dromedarii 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; immatures feed on rodents and other small mammals, birds, and reptiles.

H scupense (H detritum), is a two-host or one-host species; both adults and immatures 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 fall), nymphs (winter), and adults (spring). H scupense is a vector of Theileria annulata, T equi, and Babesia equi.

In addition to the several species already mentioned, the African savannas harbor four other Hyalomma spp of livestock and wildlife: H truncatum (southeastern Egypt to southern Africa), H albiparmatum (southern Kenya, northern Tanzania), H impressum (western Sudan and West Africa), and H nitidum (Central African Republic and West Africa). Immatures of these three-host species generally infest small mammals, less often birds and reptiles. H truncatum, which causes bovine sweating sickness and lameness and also human and ovine tick paralysis, is a vector of Crimean-Congo hemorrhagic fever virus, Coxiella burnetii(Q fever), Rickettsia aeschlimannii, and Rickettsia mongolotimonae.

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