East Coast fever

East Coast fever is a disease of cattle caused by the protozoan parasite,Theileria parva. It excludes diseases caused by other Theileria. T. annulata is sometimes erroneously blamed for East Coast Fever. However, T. annulata causes tropical theileriosis, also known as Mediterranean theileriosis, which is different from East Coast Fever. T. parva was first described in 1902 in Zimbabwe, and was misdiagnosed as redwater (disease caused by Babesia bigemina). Theileriosis is found in Swaziland, Zimbabwe, Zambia, Tanzania, Kenya, and Uganda. The primary vector for T. parva is Ripicephalus appendiculatus. Theileria are interesting because they are the only eukaryotic organisms known to transform lymphocytes.^[1] The intermediate hosts for T. parva are cattle; potentially all cattle. The definitive hosts are the ticks. Native cattle are often resistant to the parasite. This is not to say they do not suffer from the parasite; they do. They are hosts to the parasite, but do not suffer as severely as foreign cattle. ^[2][3]

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T. parva infects ticks, which then infect cattle. Mortality can be up to 100%, with death occurring around 18-30 days after the initial attachment of infected ticks. This is 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 to limited to fever, enlarged lymph nodes near the tick bite. Smears and stains can also be done to check for the parasite. Schizonts (aka meronts, or segmentors) can be found in infected lymphocytes. Pathology includes but is not limited to anorexia, dyspnea, corneal opacity, nasal discharge, frothy nasal discharge, diarrhea, pulmonary edema, leukopenia, and anemia. After this, endemic cattle that are given medication sometimes recover to varying degrees, or death follows due to blocked capillaries and parasites infecting the central nervous system. ^[4] Cattle that are endemic and manage to survive tend to be carriers. Control for the most part, is most effective if there are pre-infection vaccinations done. Once infected, it is difficult to get rid of the parasites. If the cattle are infected, there are pour-on and soak medicines that can be introduced to kill off the ticks, but it must be done frequently (monthly usually, thus, this is costly), leaves residues in milk and meat, and doesn't help the already-infected cattle. In addition, it is difficult to kill T. parva in lymphocytes once the first incubation has gone through, because T. parva do not synchronize their reproduction, so there are T. parva in many different life-cycle stages after a while.

References

1. ^ http://www.sciencemag.org/cgi/content/full/sci;309/5731/72
2. ^ NORVAL, R.A., PERRY, B.D., AND YOUNG, A.S. The Epidemiology of Theileriosis in Africa. Academic Press: London, 1991.
3. ^ http://www.ilri.org/
4. ^ MORRISON, W.L., GODDEERIS, B.M., BROWN, W.C., BALDWIN, C.L., and TEALE, A.J. 1989. Theileria parva in cattle: Characterization of infected lymphocytes and the immune response they provoke. Vet. Immun. Immuno. Path., 20: 213-217.