East Coast fever
East Coast fever (theileriosis) is a disease of cattle, sheep and goats caused by the protozoan parasite Theileria parva. The term excludes diseases caused by other Theileria, such as tropical theileriosis (also known as Mediterranean theileriosis), caused by T. annulata, and human theileriosis, caused by T. microti.
East Coast fever is probably the most important livestock diseases in Africa, causing an annual loss of 1.1 million cattle and $168 million in 1992. It is found in Sudan, South Africa, the Democratic Republic of Congo, Swaziland, Zimbabwe, Zambia, Tanzania, Kenya, and Uganda. The primary vector for T. parva is Rhipicephalus appendiculatus.
Theileria species are the only eukaryotic organisms known to transform lymphocytes. The intermediate hosts for T. parva are cattle. The definitive hosts are the ticks. Native cattle are often resistant to the parasite, but not without symptoms. They are hosts to the parasite, but do not suffer as severely as foreign cattle.
Clinical signs and diagnosis
Mortality can be up to 100%, with death occurring around 18–30 days after the initial attachment of infected ticks, because the incubation required is around 10–25 days, and the parasite spreads quickly and is rather aggressive.
Clinical signs for diagnosis include, but are not limited to, fever and enlarged lymph nodes near the tick bite(s). Smears and stains can also be done to check for the parasite. Schizonts (meronts, or segmentors) can be found in infected lymphocytes. Pathology includes anorexia, dyspnea, corneal opacity, nasal discharge, frothy nasal discharge, diarrhea, pulmonary edema, leukopenia, and anemia. Endemic cattle given medication sometimes recover to varying degrees, or death follows due to blocked capillaries and parasites infecting the central nervous system. Cattle that are endemic and manage to survive tend to be carriers.
A form of East Coast fever called corridor disease is observed when the organism is transmitted from the African buffalo to cattle. Another form, called January disease, only occurs over the winter months in Zimbabwe due to the tick lifecycle.
For diagnosis, post mortem findings are characteristic and mainly include damage to the lymphoid and respiratory systems.
Treatment and control
The classical treatment with tetracyclines (1970–1990) cannot provide efficiency more than 50%.
Since the early 1990s, buparvaquone is used in bovine theileriosis with remarkable results (90 to 98% recovery).
Other than the buparvaquones, other chemotherapeutic options are the parvaquones, e.g. Clexon. Halofuginone lactate has also been shown to have an 80.5% efficacy against Theirelia parva parva infections. The ultimate factor that causes death is pulmonary edema. In May 2010, a vaccine to protect cattle against East Coast fever reportedly had been approved and registered by the governments of Kenya, Malawi and Tanzania. This consists of cryopreserved sporozoites from crushed ticks, but it is expensive and can cause disease.
Control of the disease also relies on tick control and the development of disease-resistant ticks. Control of ticks of domestic animals is a major concern in tropical countries with large livestock populations, especially in the endemic area of East Coast fever. Chemical pesticides (acaricides) are applied in dipping baths or spray races, and use of breeds of cattle with good ability to acquire immune resistance to the vector ticks are used to control the measure.
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