The Ixodidae

Rhipicephalus spp.

The first two tick species we have to do with in this genus are arguably the best-known tick in the world (Rhipicephalus microplus), and in southern Africa (Rhicephalus decoloratus). These ticks were previously known as Boophilus microplus and Boophilus decoloratus. Their names were changed to Rhipicephalus (Boophilus) microplus and to Rhipicephalus (Boophilus) decoloratus in 2003 and in a list of valid tick names that was published in 2010 they are now simply known as Rhipicephalus microplus and Rhipicephalus decoloratus. These name changes have caused a lot of controversy, but as they have been well motivated by respected acarologists R. microplus and R. decoloratus are likely to become the accepted scientific names.

Rhipicephalus (Boophilus) decoloratus – African blue tick

The mouthparts are short and the dentition on the hypostome is arranged in two columns, each consisting of numerous rows each of which consists of three denticles (3/3 dentition). The internal margin of the first segment of each palp has a bristle-bearing protuberance. The basis capituli is hexagonal in shape. The conscutum of the male is yellowish in colour and often so poorly sclerotized that the outlines of the gut can be seen through it. There are numerous fine hairs on the conscutum of males and the scutum of females. The eyes are difficult to see, and in the female two distinct grooves divide the scutum into a central yellow area and two lateral areas that are reddish-brown. There are no festoons. A small caudal process is present on the males and the adanal plates have a long, narrow posteriorly directed internal spur and a shorter external spur. The tips of the adanal and accessory adanal plates can be seen from above where they protrude beyond the posterior margin of the conscutum. The engorged female is blue in colour, frequently with a constriction in its middle and a rather soft-looking integument. The segments of the pale yellow, slender legs are beady in appearance.

Cattle, impalas (Aepyceros melampus), eland, nyalas (Tragelaphus angasii) bushbuck (Tragelaphus scriptus), greater kudu (Tragelaphus strepsiceros) and also horses and zebras are hosts of R. decoloratus. The sides of the body, shoulders, neck and dewlap are preferred sites of attachment. The immature stages may be found on the tips and upper edges of the ears and on the legs.

Rhipicephalus microplus and decoloratus

Rhipicephalus decoloratus requires moisture and warmth. In South Africa it is found in the coastal regions of the Western and Eastern Cape Provinces, throughout KwaZulu-Natal, Mpumalanga, Gauteng, Limpopo and North West Provinces and the eastern half of the Free State. It is distributed through most of the wetter regions of South Africa, except for those localities at which it has been replaced by R. microplus. However, it also occurs in cold mountainous areas such as the Drakensberg range and parts of Lesotho. It is absent from the drier parts of South Africa, which receive an average annual rainfall of less than 380 mm, including the western Free State, the central Karoo, Bushmanland and little Namaqualand. In the generally arid territory of Namibia it is present only in localized areas in the north, and in Botswana it is restricted to the higher rainfall eastern border areas and a few scattered localities in the north. It is also present in the eastern half of Zimbabwe, Angola, much of Zambia, Malawi, southwestern and northern Tanzania, Burundi, Uganda, western Kenya and in the wetter highlands and sub-highlands of Ethiopia. It is also found in most countries of sub-Saharan West-Africa.

Rhipicephalus decoloratus is a one-host tick. The engorged females lay 1 000 to 2 500 eggs about 1 week after detaching from the host. These eggs hatch in 3 to 6 weeks and the larvae climb up the vegetation and wait there for a host. They attach, engorge and moult to the nymphal stage on the host after a week, the nymphs attach, engorge and moult to adults on the host after a week, the adults attach, partially engorge, mate and the females fully engorge and drop off after a week. They therefore spend about 3 weeks on the host animal and the life cycle, including the non-parasitic phase, can be completed in approximately 2 months. More than one life cycle can be completed annually.
The ticks are active throughout the year where the climate is warm enough, with a peak in abundance during spring and another during late summer and autumn. Large numbers of synchronously hatching larvae are present on the vegetation and on hosts in spring. In cooler regions there may be little activity in the winter months.
Rhipicephalus decoloratus transmits Babesia bigemina to cattle. This infection is transmitted only b

the nymphal and adult stages after it has passed transovarially from one generation to the next. The incubation period in cattle is 12 to 14 days. Once established in the tick host B. bigemina can be transmitted by many successive generations of ticks without their acquiring new infection. Rhipicephalus decoloratus also transmits Anaplasma marginale to cattle, and Borrelia theileri, the cause of spirochaetosis, to cattle, sheep, goats and horses.

Rhipicephalus microplus - Asian blue tick

Adults of R. microplus are slightly larger than those of R. decoloratus, and the scutum is slightly redder in colour, but they are otherwise very similar in general appearance. The dentition on the hypostome is arranged in two columns each consisting of numerous rows and each row consists of four denticles (4/4 dentition). The inner margin of the first segment of the palps is concave and bears no bristle. A small caudal process is present on the males and the internal spur on the adanal plates is approximately as long as the external spur and is not as prominent as that of R. decoloratus.

Domestic cattle are probably the only really effective hosts of this tick, but domestic goats sharing pastures with infested cattle have now also been found to be infested and as female ticks successfully engorge on the goats it is possible that the life cycle of R. microplus can be completed in the absence of cattle. More and more records of R. microplus on wildlife are being reported and ticks have been found on grey rhebok and eland in the Western Cape Province and on deer in South America.

It has been postulated that R. microplus was introduced into East and South Africa from Madagascar, where it had originally arrived with cattle from southern Asia. In South Africa it is now established in ever increasing areas along the southern and eastern coasts of the Western and Eastern Cape Provinces and of KwaZulu-Natal. It is also present in the coastal regions of Mozambique, Tanzania and Kenya. In the interior it is found in scattered localities in Mpumalanga and Limpopo Provinces, South Africa, in parts of the eastern and central provinces of Zambia, throughout Malawi and to the east and north of Lake Malawi in Tanzania. There is evidence that where favourable moist and warm climatic conditions exist it competes with and is able to replace the indigenous R. decoloratus. R. microplus spread into Zimbabwe in the 1970s, when dipping was disrupted during the pre-independence war, and replaced R. decoloratus in several areas. By 1988 it had disappeared, possibly because of drought and the reintroduction of dipping. In Zambia, though, its westward spread appears to be continuing. In Mozambique it has completely displaced R. decoloratus at least as far north as Tete Province, while it has also recently been introduced into West Africa where it is apparently flourishing. It would seem that R. microplus has adapted to most conditions in Africa: the constant warm and moist regions of West Africa with its lush vegetation, the coastal areas of South Africa with their adjoining drier regions, the inland regions of the north-eastern regions of the Eastern Cape Province, where snow may fall in winter, and the extremely hot and dry regions of Tete Province, Mozambique, where there is scarcely a blade of grass to be found during winter and spring.

Rhipicephalus microplus has a one-host life cycle of which the parasitic portion takes approximately 21 days to complete on the host. Its total life cycle (including the off host period during which the detached female lays eggs, the larvae hatch from the eggs and the larvae quest for hosts from the vegetation) is approximately 1 week shorter than that of R. decoloratus. Females lay approximately 500 eggs more than do R. decoloratus females, and like R. decoloratus it is able to complete several generations in one year.

Rhipicephalus microplus may be present in variable numbers throughout the year. The largest numbers of larvae are usually present on pastures and on hosts in spring, and successive lesser waves of questing larvae then occur through the summer and into the cooler autumn and early winter months. Theoretically, only larvae of this one-host tick should quest for hosts from the vegetation, but male ticks have also been collected from the vegetation, implying that they must have detached shortly before or after moulting and were now questing from the vegetation for a second host.
The tick transmits bovine babesiosis (Babesia bovis and B. bigemina). Babesia bovis infection is acquired by the adults of one generation of ticks and transmitted transovarially by the larvae of the next generation and all infestation is then lost by them. It also transmits bovine anaplasmosis (Anaplasma marginale) and spirochaetosis (Borrelia theileri).

Rhipicephalus appendiculatus - Brown ear tick

The tick is a uniform brown colour. The mouthparts are short and the basis capituli, particularly of the female, is hexagonal in shape. The anterior process of coxa I is visible from the dorsal surface. The cervical fields are the shape of scalpel-shaped depressions. The eyes are flat. There is a mixture of medium-sized and fine punctations present in the middle of the conscutum and the scutum. The postero-median groove and the postero-lateral grooves on the male conscutum are fairly long and narrow. The adanal plates are fairly long and in engorged males a caudal appendage is present. In males the legs increase in size from I to IV.

Large numbers of both adult and immature ticks can be found on cattle, goats, African buffalo, eland, male nyala, greater kudu and sable antelope (Hyppotragus niger). Some adults and large numbers of immatures can occur on smaller antelopes such as impalas and only immatures on scrub hares.

The adults are found particularly on the inner and outer surfaces of the ears but do not go into the ear canals. In heavy infestations they are also found on the eyelids, around the horns, on the upper surfaces of the neck, in the tailbrush and around the anus. On cattle the immature stages attach mainly on the neck and dewlap, the cheeks, eyelids, muzzle and ears.

This tick is an eastern, central and southern African species. Its distribution extends from southern Sudan, Uganda, south-western Kenya, eastern Democratic Republic of the Congo, Rwanda and Burundi, to northern, north-eastern, central and south-western Tanzania. In southern Africa it is confined to the moister regions, which include the highlands of Malawi, Zambia, Mozambique (Angonia and Chimoio Districts), and Zimbabwe. It is also present in eastern Botswana and in Swaziland. The extent of its distribution in the coastal regions of Mozambique is unknown. In South Africa it is present in  Limpopo, North-West, Gauteng and Mpumalanga Provinces, along the east coast of KwaZulu-Natal and the coastal regions of the Eastern Cape Province to Grahamstown in the west of the latter province. There are also foci in the Ermelo and Carolina districts in Mpumalanga and Vredefort in the Free State.

Rhipicephalus appendiculatus and zambesiensis

Rhipicephalus appendiculatus survives best in woodland and woodland savanna regions with good vegetation cover. It tends to die out if overgrazing occurs and it does not survive on open plains. It was introduced into the south-eastern lowveld of Zimbabwe during the commencement of a wet cycle in 1973, and by 1982 it was estimated that more than 1 million ha of the lowveld were infested. It started to disappear from this region towards the end of a dry cycle in 1983 and by 1985 it could no longer be found.

This is a three-host tick. It feeds rapidly in all stages of development requiring only 4 to 7 days to engorge. The engorged female lays 3 000 to 5 000 eggs after detaching from the host. These eggs hatch in 20 to 90 days. The entire life cycle can be completed in 3 months but in the southern regions of the tick's distribution it probably takes a year to complete.

Rhipicephalus appendiculatus has a strictly seasonal, single annual life cycle in southern Africa. Adults occur during the rainy period (December to March), larvae in the cooler late summer to winter period after the rains (March to July) and nymphs in the winter and early spring (July to October). The pattern of seasonal occurrence is regulated by the unfed adults, which enter diapause and do not engage in host seeking until the rains start. In regions close to the equator more than one life cycle can be completed annually and no clear pattern of seasonal abundance may be evident.

This tick is the main vector of Theileria parva, the causative organism of East Coast fever in cattle. Transmission takes place from stage to stage. Benign bovine theileriosis caused by Theileria taurotragi, bovine ehrlichiosis (E. bovis) and the virus of Nairobi sheep disease are also transmitted by this tick species. It is also responsible for the transmission of Rickettsia conori to humans. It is hypothesized that the saliva of R. appendiculatus contains a toxin and if large numbers of ticks infest an animal this toxin can interfere with the immune processes of the host resulting in a loss of condition and outbreaks of babesiosis, anaplasmosis and heartwater in animals that were previously immune to these diseases. Severe infestations can lead to crumpling of the ear and infestations of the ear with the larvae of Chrysomya bezziana may occur.

Rhipicephalus zambeziensis - Lowveld brown ear tick

Rhipicephalus zambeziensis is closely related to R. appendiculatus, and the two are morphologically very similar. The major difference between the adults of the two species is that R. zambeziensis has more conspicuous punctations on the scutum. In the females the genital aperture of R. appendiculatus is shaped like a deep bowl with sloping sides, whereas that of R. zambezienis is shaped like a pot with nearly upright sides. The immature stages are more easily differentiated than the adults.

The tick has the same hosts as those used by R. appendiculatus during its adult and immature stages. Adults are found on the head and ears and on the muzzles, and immatures on the feet and legs.

Rhipicephalus zambeziensis replaces R. appendiculatus in the hot, dry river valley systems of south-eastern Africa (Luangwa, Kafue, Zambezi, Sabi and Limpopo Valleys) that separate the major highland areas. It is present in the dry environments of northern Namibia and in the lowland areas of the Mozambique interior. The distributions of R. zambeziensis and R. appendiculatus overlap where there are gradual transitions between wet and dry areas. This occurs in parts of the eastern and southern provinces of Zambia bordering the Zambezi Valley, eastern Botswana and in North-West, Limpopo and Mpumalanga Provinces, South Africa. Some interspecific hybridization may occur. R. zambeziensis is absent from semi-desert and desert areas.

This is a three-host tick. Adults are most numerous in the late summer, larvae during autumn and winter and nymphs during winter and spring.

Rhipicephalus zambeziensis is the vector of Corridor disease (T. parva), benign bovine theileriosis (T. taurotragi) and ehrlichiosis (E. bovis).

Rhipicephalus evertsi evertsi - the red-legged tick

Conscutum and scutum are densely punctate and very dark brown contrasting with the reddish-orange body wall. The eyes are convex and orbited and the legs are reddish-orange. The adanal plates are triangular in shape and large, and the circum-spiracular integument is covered with dense prominent setae.

Adults prefer horses, zebras, elands, cattle and sheep. Larvae and nymphs utilise the same hosts as the adults and also scrub hares and various antelopes. The adults are found on the hairless area around the anus as well as the inguinal region of equids and sheep. The immature stages attach deep in the ear canals. Several hundred of these may be recovered from the ear canals of zebras.

Of the 60 or more Rhipicephalus spp. that occur in Africa R. evertsi evertsi is the most widespread, with the majority of sub-Saharan countries reporting its presence. It is most common in the eastern part of the continent, from Eritrea and Sudan in the north to South Africa in the south. With the exception of the Northern Cape Province, where its distribution is somewhat limited, it occurs virtually throughout South Africa. It tolerates a wide range of climatic conditions and in southern Africa the main factor limiting its distribution in the west is increasing aridity, with the critical rainfall level being about 250 to 280 mm per annum.

This is a two-host tick. After dropping from the host the engorged females lay 5 000 to 7 000 eggs and then die. The eggs hatch and the larvae climb on to the vegetation and then on to the first hosts and attach deep in the ear canals where they moult to the nymphal stage after about 1 week. The nymphs engorge in about 1 week and then detach and drop off the host to moult to the adults. The adults attach to the second and final host on which they remain for about 6 to 12 days.

These ticks are active mainly during the summer but are present throughout the year in warm regions. In KwaZulu-Natal, South Africa, the immature stages are active from November to June and the adults from January to May. In Limpopo Province the immature stages are most abundant from April to September and the adults from September to March. More than one life cycle can be completed in a year.

Rhipicephalus evertsi evertsi may play a role in the transmission of T. parva to cattle, but if it does it is not an important vector. It transmits Theileria equi and Babesia caballi to horses stage to stage only. T. equi and B. caballi are also transmitted intra-uterinely in horses. It has been demonstrated experimentally that it can transmit B. bigemina transovarially to cattle. Stage to stage transmission of Theileria separata to sheep also occurs. Transmission of B. theileri, the cause of spirochaetosis in cattle, horses, sheep and goats has also been reported. The saliva of engorging female ticks contains a toxin that causes paralysis, particularly in lambs, but it may also affect calves and adult sheep. This toxicosis is known as spring lamb paralysis because of its seasonal occurrence. In the eastern highveld regions of the Mpumalanga and Free State Provinces, South Africa the synchronous moulting of free-living over-wintered nymphs gives rise to large numbers of adults on spring-born lambs. Several females are necessary to produce paralysis and they must have fed for about 5 days and weigh between 15 and 21 mg each. The clinical signs can be reversed by removal of the ticks. Large infestations of immature ticks may damage the ear canal of its host.
A very similar tick, Rhipicephalus evertsi mimeticus, known as theNamibian red-legged tick,looks like R. evertsi evertsi, but has red and ivory-coloured banded legs similar to those of certain Hyalomma spp. However, the structure of its capitulum and its shorter mouthparts readily distinguish it from the Hyalomma spp.

Rhipicephalus evertsi mimeticus would seem to have the same host preferences, predilection attachment sites and life cycle as R. evertsi evertsi. The adults are most numerous from November to May and the immature stages in February and March and from May to September. This tick occurs in western Botswana, central and northern Namibia and southern and western Angola.

R. evertsi mimeticus transmitsTheileria equi, the cause of equine piroplasmosis, and Theileria separata, the cause of ovine theileriosis.

Rhipicephalus evertsi evertsi and pravus

Rhipicephalus pravus

Its conscutum and scutum narrow and punctate, eyes convex and prominent and cervical fields narrow and nearly parallel with each other. Large triangular adanal plates present on males and engorged males have a narrow fairly long caudal process.

All stages of development infest hares, adults on cattle, sheep and goats and wild ruminants. Immature stages are found on elephant shrews. Adults attach on the head and ears, and also on the lower neck, abdomen, udder, perineum, groin and heels of their larger hosts.

Rhipicephalus pravus is present in eastern Ethiopia, Somalia, Kenya, and north-eastern Tanzania.
It is a three-host tick. A long dry season seems important in the life cycle of this tick. Adults are most numerous during the rainy season in Ethiopia. The immature stages are present on hares during the dry season in Kenya.

Rhipicephalus simus - Glossy brown tick

(In East Africa R. simus is replaced by Rhipicephalus praetextatus, which morphologically is nearly identical to R. simus).

The conscutum and scutum are shiny and dark or reddish-brown. There are four definite longitudinal rows of large punctations referred to as the “simus” pattern on the conscutum of the male, on which there are also numerous small to minute punctations. Posterior grooves are absent or very indistinct. The caudal process is bluntly rounded in engorged males, and the adanal plates are large and almost kidney-shaped. The posterior margin of the female scutum is usually smoothly rounded and the external margin of the broad cervical fields is clearly demarcated by irregualar rows of punctuations. The shape of the female genital aperture is a truncated U-shape, diverging anteriorly.
Adult ticks infest cattle, sheep goats, horses and dogs, large carnivores, zebras, warthogs, rhinoceroses. The larvae and nymphs infest rodents. The adults are found in the tail switch of cattle and zebras and on the head and shoulders of dogs and warthogs, as well as around the feet of sheep and cattle.

Rhipicephalus simus is widespread in the moister eastern regions of southern Africa, but is never very numerous. It is a three-host tick of which the adults are present in summer, larvae autumn to winter on their rodent hosts, and the nymphs winter to spring on rodents.

Rhipicephalus simus can transmit Anaplasma marginale, the cause of anaplasmosis or gallsickness in cattle, stage to stage and intrastadially.

Rhipicephalus pravus and simus