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Ticking time bomb

Written by  Dr Joan Kleynhans-Jordaan
| in Veearts
| March 3, 2016

Ticks are responsible for significant losses in livestock production. They lower productivity and fertility and transmit diseases which often cause death. They are economically the most important ectoparasites of cattle.

Ticks suck blood, damage hides and skin, introduce toxins and predispose cattle to myiasis and dermatophilosis. They also reduce body weight gains and milk yield, and create sites for secondary invasion by bacteria. The following ticks, which are of veterinary importance, are known to occur in the Eastern Cape.

veearts march 2016 1Amblyomma hebraeum - Bont tick

This tick can transmit Ehrlichia ruminantium (heartwater) and Theileria mutans (benign theileriosis). Adults feed on livestock and large wild ruminants, as well as warthogs and rhinos. Immature ticks also are found on these animals, but also on small antelopes, scrub hares, leopard tortoises and helmeted guinea fowl.

In cattle, adult ticks are usually found on the hairless skin under the tail, in the lower perineal area, on the udder, the prepuce and testes, as well as the axilla. In sheep and goats they are found around the feet.   Larvae attach to feet, legs and muzzle and nymphs are found on feet, legs, groin, sternum and neck.

“Larvae attach to feet, legs and muzzle and nymphs are found on feet, legs, groin, sternum and neck.”

Amblyomma hebraeum requires three hosts to complete its lifecycle. When a host is in the vicinity, the adults and nymphs will scuttle along the ground to reach it, especially if the host is already infested with pheromone-producing male ticks.

This tick is found in the coastal belt of the Eastern Cape and further north. It needs warm, moist conditions and brush and bush. It does not survive in open grasslands.

A. hebraeum carries heartwater, as well as Theileria mutans and Theileria velifera which cause benign bovine theileriosis. When A. hebraeum attach between the hooves of goats in large numbers, they can cause foot abscesses.

veearts march 2016 2Rhipicephalus (Boophilus) micro plus - Asian blue tick

This tick is significant because it transmits both Babesia bigemina and Babesia bovis. Adults of one generation acquire the infection and transmit it transovarially. The larvae of the next generation transmit the disease to new susceptible hosts.

Bovine anaplasmosis (Anaplasma marginale) and spirochaetosis (Borrelia theileri) are also transmitted by R.(B.) microplus.  This tick is usually found on cattle and occasionally on goats. It has only rarely been found on wildlife.

R.(B.) microplus is believed to have been introduced into Southern Africa from Madagascar, although it originally came to Madagascar with cattle from southern Asia. The tick is now established in scattered areas of the southern and eastern Cape coast, KwaZulu-Natal and in specific localities in Mpumalanga and Limpopo. Where climatic conditions are warm and moist, R.(B.) microplus is able to replace the indigenous R.(B.) decoloratus. This is the case in the eastern regions of the Eastern Cape.  

R.(B.) microplus is a one-host tick and completes its lifecycle in two months. In areas with a prolonged rainy season, several generations complete their lifecycle in a season.  All  the stages of development are present on the same host simultaneously. If 70 engorged females are present, the host will have about 10,000 ticks in total.  Numbers vary with the seasons. In late spring, pastures contain large numbers of larvae. Successive waves of larvae occur until early winter.

“If 70 engorged females are present, the host will have about 10,000 ticks in total.”  

veearts march 2016 3Rhipicephalus (Boophilus) decoloratus -  African blue tick

This tick is responsible for transmitting Babesia bigemina (African redwater) to cattle. Ticks pick up the organism from infected cattle and only transmit it as nymphs and adults after it has been passed transovarially from one generation to the next. In cattle the incubation period is 12 to 14 days. Once B. bigemina is established in the tick population, it can pass to many successive generations without them acquiring new infection.

R.(B.) decoloratus is also responsible for the transmission of Anaplasma marginale to cattle. It also transmits Borrelia theileri, the cause of spirochaetosis in cattle, sheep, horses and goats. Eland can be asymptomatic carriers of A. marginale and may serve as reservoirs of infection.

Besides cattle and eland, R.(B.) decoloratus also occurs on impala, bushbuck, greater kudu, horses and zebra. Preferential sites of attachment are sides of the body, shoulders, neck and dewlap. Immature stages can also be found on ear tips, upper edges of ears and on the legs.

This tick occurs through most of the wetter regions of South Africa, except where it has been replaced by R.(B.) microplus. It also occurs in cold mountainous regions .

R.(B.) decoloratus has a longer life-cycle than R.(B.) microplus. Males of the latter mature faster and will cross-mate with the former, causing the production of sterile eggs. R.(B.) microplus also has higher egg production. Over time it can displace R.(B.) decoloratus.

R.(B.) decoloratus is a one-host tick species. Where the climate is warm enough, it is active year round, with peaks in spring and late summer to autumn. In colder regions the ticks are less active in winter.

Both R.(B.) decoloratus and R.(B.) microplus can have significant effects on cattle production.

veearts march 2016 4Rhipicephalus appendiculatus - Brown ear tick

This tick is the main vector of Theileria parva, which causes East Coast fever and corridor disease in cattle. Transmission in ticks takes place from stage to stage. The T. parva strain which causes corridor disease in cattle is carried by buffalo. However, disease-free buffalo in the Eastern Cape should be Theileria parva free.  

Theileria taurotragi, the cause of benign bovine theileriosis and bovine anaplasmosis is also transmitted by R. appendiculatus. T. taurotragi may cause severe or fatal disease in eland.

R. appendiculatus can also transmit Rickettsia conorii to humans.

“Large infestations with R. appendiculatus also suppress immunity in their hosts, possibly via a toxin in their saliva.”

Large infestations with R. appendiculatus also suppress immunity in their hosts, possibly via a toxin in their saliva. This may lead to loss of condition and outbreaks of babesiosis, anaplasmosis and heartwater in animals that were previously immune.    Severe infestations can also lead to ear damage, which may then become infested with blowfly larvae.

This tick occurs in the Eastern Cape coastal regions to Grahamstown in the west, as well in many other locations in SA and Africa.

R. appendiculatus is a three-host tick. In its southern range the life-cycle takes a year to complete and is strictly seasonal. In the rainy season from December to March adults are seen. Larvae occur in the cooler, drier months between March and July  and nymphs in winter and early spring (July to October).  Host species are cattle, goats, African buffalo, eland and male nyala.

veearts march 2016 5Rhipicephalus evertsi evertsi - Red legged tick

This tick may play a role in the transmission of Theileria parva to cattle, but is not regarded as important in this regard. Babesia caballi and Babesia equi is transmitted to horses but only between tick life-cycle stages and not intra-ovarially. Horses can transmit B. equi and B. caballi to their foals in utero.

R. evertsi evertsi has been demonstrated to transmit B. bigemina to cattle intra-ovarially. Transmission of B. theileri, which causes spirochaetosis in cattle, horses, sheep and goats has been reported. Engorging female ticks have toxic saliva that can cause paralysis, especially in lambs (spring lamb paralysis), but also in calves and adult sheep. The clinical signs can be reversed by removal of the ticks. Large numbers of immature ticks may damage the ear canal of hosts. Preferred hosts of adult ticks are horses, zebra, eland, cattle and sheep. Larvae and nymphs infest the same hosts as well as scrub hares and various antelope. Adults are found on hairless perianal and inguinal areas in horses and sheep. Immatures attach deep in the ear canal. It is a two-host tick. They are mainly active in summer.

According to correspondence from Dr. Leon de Bruyn, a veterinary surgeon in Port Alfred, Bathurst is often considered the tick capital of the world.  “We have an abundant population of Amblyomma, Rhipicephalus appendiculatus and evertsi ticks peaking in summer and Rhipicephalus decoloratus and microplus blue ticks all year round.  We therefore have heartwater, ear problems and tick related abscesses and screwworm myiasis all year round, but peaking in summer.

“We have an abundant population of Amblyomma, Rhipicephalus appendiculatus and evertsi ticks peaking in summer and Rhipicephalus decoloratus and microplus blue ticks all year round.”  

“We are also an endemic African redwater and anaplasmosis area, but have had an increased prevalence of Asiatic redwater in the last ten years as the pantropical blue tick marches west and south. These outbreaks often occur in autumn and early winter.

“We occasionally have cases of theileriosis in very heavily infested cattle, but it is more of a problem in sable antelope calves,” he concludes.

Further reading:
Good images of ticks and distribution: http://www.afrivip.org/sites/default/files/Ticks-importance/