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 R sanguineus and R (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. 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 three-host, but in the Mediterranean climatic zone (long, warm summer with low rainfall) R bursa has a two-host cycle. In sub-Saharan Africa with long dry seasons, R evertsi and R glabroscutatum also have two-host cycles. In contrast, each of the five species in subgenus Boophilus has a one-host life cycle that may be completed in 3–4 weeks (see below).
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 based on molecular analyses.
Subgenus Boophilus spp
Each of the five Rhipicephalus (Boophilus) spp 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 (B) microplus in the Indian region, have developed resistance to feeding by large numbers of ticks and are used (purebred or crossbred) in integrated control programs. R (B) microplus, considered the world’s most important tick parasite of livestock, has been 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 (B) microplus and R (B) annulatus were eradicated from the USA after a long, costly control program. Constant surveillance is maintained to prevent their reintroduction.
R (B) annulatus of southern former USSR, 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 (B) annulatus populations.
R (B) decoloratus, which ranges from southern Africa to the Sahara, is being replaced in the southeastern part of this area by R (B) microplus. In more humid West African zones, R (B) annulatus mixes with or is totally replaced by R (B) geigyi. Scattered R (B) geigyi populations are found as far east as southern and central Sudan. The only boophilid restricted to sheep and goats (and occasionally horses) is R (B) kohlsi of Syria, Iraq, Israel, Jordan, western Saudi Arabia, and Yemen. R (B) microplus is an experimental vector of Babesia equi and has been collected from the nasal passages of equids in Panama. This tick and R (B) annulatus are major vectors of Babesia bigemina, B bovis, and Anaplasma marginale. R (B) decoloratus is an efficient vector of B bigemina and A marginale but does not transmit B bovis or B equi.
Subgenus Rhipicephalus spp
Tropical Asia is the home of five Rhipicephalus (Rhipicephalus) spp; 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. 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 two-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, people, and infrequently dogs. It causes ovine paralysis and transmits Crimean-Congo hemorrhagic fever virus and other viruses to people, and 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 (Cowdria) ruminantium (the agent of heartwater), and Trypanosoma vivax (an agent of sleeping sickness).
The best known rhipicephalids, cumulatively identified 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 so-called "temperate lineage," is present throughout most of Europe as well as in temperate regions of the New World (Argentina, southern Brazil, Chile, Uruguay, USA, and Canada). Conversely, the so-called "tropical lineage" of brown dog ticks is found circumglobally in tropical areas with annual average temperature between 20° and 30°C, including Africa, tropical Asia, Australia, Oceania, and from the USA-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 the "tropical lineage" and other potential lineages of brown dog ticks has not been ascertained.
Whereas R sanguineus sensu stricto feeds preferentially on wild and domestic canines in all life stages, ticks of the "tropical lineage" are known to parasitize wild and domestic carnivores, sheep, goats, camels, other livestock, and various wild mammals, especially hares and hedgehogs. Immatures of the "tropical lineage" in nature feed on small mammals. However, in urban situations everywhere, dogs are primary hosts of both immatures and adults. People are attacked infrequently, more often in situations when children play and sleep in close contact with heavily infested dogs. In heavily infested houses and kennels, newly active adults and nymphs are frequently seen climbing walls from floor-level cracks.
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, vector competence of the two species of R. sanguineus sensu lato group may also differ 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, 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. 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, R 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 savannas, moist broadleaf forests, and dry shrublands 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 people. 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 two-host African rhipicephalids are two subspecies of R evertsi 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 birds. 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, are found west of the Nile. On bovids and equids, immatures 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 their 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 Tparva (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 southeastern Cape Province, South Africa. Horses, kudu, and other small antelope are also infested. The few records of immatures 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, currently under taxonomic study, consists of four 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, 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 (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 and R gertrudae), East Africa (R compositus and R longus), and West Africa to southwestern Sudan (R pseudolongus).
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 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 species parasitize livestock, dogs, wild carnivores, large and medium-sized game animals, and people. Occurrence and densities on livestock are inexplicably erratic. Immature stages feed on the common burrowing rodents in savannas. Both species cause tick paralysis of people 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 due to misidentification. The chief feeding sites of both on livestock and wildlife are the legs and tailbrush, but 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.
R sanguineus and R turanicus of the R sanguineus group are described above. 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 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.
