East Coast Fever
East Coast fever, an acute disease of cattle, is characterized usually by high fever, swelling of the lymph nodes, dyspnea, and high mortality. Caused by Theileria parva , it is a serious problem in east and central Africa.
East Coast fever (ECF), a form of bovine theileriosis, is a tick-transmitted protozoal disease of cattle characterized by high fever and lymphadenopathy. The disease causes high mortalities in breeds nonindigenous to the endemic areas, and is confined to eastern, central, and parts of southern Africa.
The first clinical sign of ECF in cattle appears 7 to 15 days after attachment of infected ticks. This is seen as a swelling of the draining lymph node, usually the parotid, for the ear is the preferred feeding site of the vector. This is followed by a generalized lymphadenopathy in which superficial subcutaneous lymph nodes such as the parotid, prescapular, and prefemoral lymph nodes, can easily be seen and palpated (Fig.).
In ECF there is generalized lymphadenopathy; note the prescapular lymph node.Fever ensues and continues throughout the course of infection. This rise in temperature is rapid and is usually in excess of 103 F (39.5 C) but may reach 106 F (42 C). Anorexia develops, and loss of condition follows. Other clinical signs may include lacrimation, corneal opacity, nasal discharge, terminal dyspnea, and diarrhea. Before death the animal is usually recumbent, the temperature falls, and there is a severe dyspnea due to pulmonary edema that is frequently seen as a frothy nasal discharge. Death usually occurs 18 to 30 days after infestation of susceptible cattle by infected ticks. Mortality in fully susceptible cattle can be nearly 100 percent. The severity and time course of the disease depend on, among other factors, the magnitude of the infected tick challenge, for ECF is a dose- dependent disease, and on the strain of parasites. Some stocks of parasites cause a chronic wasting disease. A fatal condition called “turning sickness” is associated with the blocking of brain capillaries by infected cells and results in neurological signs. In recovered cattle, chronic disease problems can occur that result in stunted growth in calves and lack of productivity in adult cattle. However, this syndrome tends to be in the minority of recovered clinical cases; in a majority of cases, asymptomatic carriers can be recognized with apparently little or no effect on their productivity.
An occult phase of 5-10 days follows before infected lymphocytes can be detected in Giemsa-stained smears of cells aspirated from the local draining lymph node. Subsequently, the number of parasitized cells increases rapidly throughout the lymphoid system, and from about day 14 onwards, cells undergoing merogony are observed. This is associated with widespread lymphocytolysis, marked lymphoid depletion, and leukopenia. Piroplasms in RBC infected by the resultant merozoites assume various forms, but typically they are small and rod-shaped or oval.
East coast fever is only found in association with its known tick vectors, Rhipicephalus appendiculatus, R. zembeziensis and possibly R. duttoni and R. nitens (2). A febrile disease with signs of enlarged lymph nodes associated with infestation by tick vectors is suggestive of ECF. An acute disease with high mortality on farms, where tick control is not effectively applied, also is suggestive of ECF. In many epidemiological situations, high mortality occurs only in calves; the adult cattle represent immune survivors.
In the field, diagnosis is usually achieved by finding Theileria parasites in Giemsa-stained blood smears and lymph node needle biopsy smears (Fig.).
ECF – Lymphoblasts containing Theileria parasites.
Specimens for Laboratory
Specimens consisting of buffy coat smears air-dried and fixed in methanol; lymph node impressions air-dried and fixed in methanol; lymph nodes, spleen, lung, liver, and kidney samples for histopathology; and serum should be collected.
The demonstration of schizont-infected cells in lymph node samples is diagnostic of ECF. Small piroplasms in erythrocytes are suggestive of ECF, but diagnosis must be confirmed by the detection of schizonts. Schizonts can be detected in sections but are best seen in smears
Antibody in the mammals can be detected by a variety of serological tests of which the most widely used is the indirect fluorescent antibody test employing cell culture schizont antigen. Enzyme-linked assays have been developed using whole parasite lysates or specific antigens isolated by monoclonal antibodies. Because of the often acute nature of the disease, serological tests are useful in detecting a changed immune status of recovered animals within an exposed herd. Now DNA technologies can be applied to material from cattle and ticks, including the use of probes and the polymerase chain reaction.