East Coast fever

From Wikipedia, the free encyclopedia

East Coast fever (theileriosis) is a disease of cattle 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 among the most important livestock diseases in Africa,[1] causing an annual loss of 1.1 million cattle and $168 million, as of 1992.[2] It is found in Sudan, South Africa, the Democratic Republic of Congo,[1] Swaziland, Zimbabwe, Zambia, Tanzania, Kenya, and Uganda.[citation needed] The primary vector for T. parva is Rhipicephalus appendiculatus.[1]

T. parva was first described in 1902 in Zimbabwe, but was misdiagnosed as redwater (a disease caused by Babesia bigemina). Theileria are the only eukaryotic organisms known to transform lymphocytes.[3] The intermediate hosts for T. parva are 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.[4][5]

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. [6] 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.

[edit] References

  1. ^ a b c Olwoch, J.M., Reyers, B., Engelbrecht, F.A., and Erasmus, B.F.N. (2008). "Climate change and the tick-borne disease, Theileriosis (East Coast fever) in sub-Saharan Africa," Journal of Arid Environments, 72(2), 108-120.
  2. ^ Norval, R.A.I., Perry, B.D., and A.S. Young (1992). The Epidemiology of Theileriosis in Africa, p. 481. Academic Press, London.
  3. ^ GENETICS: Themes and Variations in Apicomplexan Parasite Biology - Roos 309 (5731): 72 - Science
  4. ^ Norval, R.A.I., Perry, B.D., and A.S. Young (1992). The Epidemiology of Theileriosis in Africa. Academic Press, London.
  5. ^ International Livestock Research Institute
  6. ^ 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.