Rhipicephalus spp - The Merck Veterinary Manual

Rhipicephalus spp

Rhipicephalid species occur in Eurasia and northern Africa (15 species) and in subSaharan Africa (~55 species). Adults of most species parasitize wild and domestic artiodactyls, perissodactyls, or carnivores. Immatures 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 3-host, but in the Mediterranean climatic zone (long, warm summer with low rainfall), R bursa has a 2-host cycle. In subSaharan Africa with long dry seasons, R evertsi and R glabroscutatum also have 2-host cycles.

Rhipicephalus sanguineus

A number of Rhipicephalus spp have long been difficult to identify or have been incorrectly identified. Current concepts of tick phylogeny, taxonomy, and nomenclature are being revised and expanded based on molecular analyses. This ongoing work is likely to expand and alter the current understanding of the phylogeny and evolution of the subfamily Rhipicephalinae (as exemplified by the current view that the genus Rhipicephalus is probably paraphyletic with respect to the genus Boophilus). Problem areas are indicated below.

Tropical Asia is the home of 5 Rhipicephalus spp ; adults of 2 species parasitize domestic animals. R haemaphysaloides infests all types of livestock, and 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. Immatures of both species feed chiefly on rodents, also on shrews, hares, and smaller carnivores.

From central Europe to Kazakhstan, R rossicus , R schulzei , and R pumilio 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, southern former USSR, India 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.

An easily recognized 2-host species, R bursa , ranges from the western Mediterranean area of Europe to Iran and Kazakhstan. Adults and immatures parasitize livestock, hares, deer, wild sheep and goats, and humans. It causes ovine paralysis and transmits Crimean-Congo hemorrhagic fever virus and other viruses to humans, and Babesia , Theileria , and Anaplasma spp to livestock.

The best known African rhipicephalid, R sanguineus , the kennel tick or brown dog tick, has traveled worldwide with domestic dogs. It is now established in buildings as far north as Canada and Scandinavia and as far south as Australia. In Africa, the Near East, and parts of southern Europe, adults parasitize wild and domestic carnivores, sheep, goats, camels, other livestock, and various wild mammals, especially hares and hedgehogs. Immatures in nature in this area feed on small mammals. However, in urban situations everywhere, dogs are virtually the only hosts of immatures and adults. Humans are rarely attacked. Strains of adult R sanguineus that feed on cattle are recorded in parts of Mexico and in Tahiti. This tick is active throughout the year in the tropics and subtropics but only from spring to fall in temperate zones. Newly active adults and nymphs are frequently seen climbing walls from floor-level cracks. R sanguineus is a vector of Babesia canis , Ehrlichia canis , Rickettsia rhipicephali , Rickettsia conorii , Crimean-Congo hemorrhagic fever virus, and Thogoto virus. In southcentral USA, R sanguineus is associated with scattered foci of Leishmania mexicana . Implications of this tick as a vector of other infectious agents require confirmation. Certain American populations have become resistant to insecticides. The hymenopteran (chalcid) parasite of ticks, 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 immatures feed in the ears of cattle, other livestock, and antelope, but also on other areas when the infestation is massive. Immatures may infest small antelope and carnivores, and occasionally rodents. Seasonal activity is closely associated with temperature and rain periods. 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 Theileria 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 Transvaal; it also is a vector of East Coast fever. Other species closely related to R appendiculatus include R nitens in the 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 savanna habitats east of the Rift Valley from southern Ethiopia to Somalia and northeastern Tanzania. Adults and immatures generally infest the same host; however, immatures 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. This tick is a vector of Babesia equi (among zebra), 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 2-host African rhipicephalids are R evertsi subspecies and R glabroscutatum . R evertsi evertsi , a large, beady-eyed, red-legged tick, a parasite of the East African zebra, parasitizes all types of herbivorous wildlife and livestock (but seldom pigs). Immatures and adults infest the same hosts; immatures are also recorded from hares. It 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, occur west of the Nile. Immatures feed in the 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 their concentrations in difficult-to-reach feeding sites. The life cycle continues through the year but slackens in cooler seasons. R evertsi evertsi transmits Babesia equi , Theileria parva (secondary vector), 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 R glabroscutatum has become a common pest of sheep, goats, and other livestock in the arid, small-shrub savanna of southeastern Cape Province, South Africa. Kudu and other small antelope are also infested. The few records of immatures are from rodents.

The R pravus group, presently under taxonomic study, consists of 4 or more species of which the adults feed on livestock and herbivorous wildlife (including hares); immatures feed on elephant shrews (insectivores), hares, and other small mammals. R pravus , a brown, convex-eyed tick, occurs in shrubby and wooded savannas in east Africa. 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 (neavi) (Botswana to Kenya and Zaire), and an as yet 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 in Namibia and South Africa ( R capensis , including the possibly synonymous R gertrudae ), East Africa ( R compositus and R longus ), and West Africa to southwestern Sudan ( R cliffordi ).

Above 5,900 ft (1,800 m) 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 to be a well-established species, is now divided into several species. In the new classification, R simus sensu stricto is found through central and southern Africa, roughly south of latitude 8 º 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 species 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 species cause tick paralysis of humans and transmit Rickettsia conorii 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. The chief feeding site of both on livestock and wildlife is the tailbrush, but other parts of the host are also feeding sites.

R sanguineus and R turanicus of the R sanguineus group are described above. Related species are R camicasi and R bergeoni of northeastern Africa, R guilhoni and R moucheti of West Africa, and 2 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 muhlensi (Kenya and southern Sudan to Central Africa). Adults of both species parasitize cattle, Cape buffalo, antelope, and big game animals; R supertritus also is found on carnivores.