Clinical and Hematological Profiles of Malaysian Ponies Experimentally Infected with a Field Strain of Trypanosoma evansi

No outbreak has been reported on Trypanosoma evansi infection in Malaysia ponies since 1983, and little is known about the interaction between T. evansi and ponies in the country. Therefore, an experimental study was designed to evaluate the pathogenicity of a local strain of T. evansi in the local ponies.

For this purpose, four healthy local ponies were inoculated with 10² live trypanosomes/kg body weight, whereas two ponies served as negative control. Blood samples and rectal temperature were collected on alternate days from both groups for 54 days. Physical examination comprised visible mucous membrane and any appearance of clinical signs were observed daily. The number of trypanosomes was estimated using the Neubauer haemocytometer method. Complete haemogram measurements were performed immediately using an automated blood cell counter and the data obtained was evaluated using the general linear model as linear regression. All infected ponies were salvaged treated with 7 mg/kg of diminazene diaceturate.

The four infected ponies developed parasitaemia on the 4^th day post-infection (DPI), whereas the first high mean of parasites count was recorded on the 8^th DPI. Parasitaemia was detected at a level that fluctuated throughout the infection period (30 days) in all infected ponies with a mean of 13.5x106 trypanosomes/ml blood on the 30^th DPI. Successive peaks of pyrexia were accompanied by the peaks of parasitaemia and the highest temperature (39.4°C) was observed on the 20^th DPI. Excessive weakness and a reduction of appetite fluctuated in the infected ponies during the infection and one animal died unexpectedly on the 23^rd DPI. The mean values for RBC, PCV, Hb and thrombocyte count were significantly lower in the infected ponies than the control groups. Neutrophil and eosinophil were significantly declined after the onset of parasitaemia, whereas monocyte increased significantly in the infected group.

The appearance of clinical signs and changes in haematological parameters suggests that Malaysian local ponies are susceptible to T. evansi infection. Treatment of the infected ponies with the recommended dosage of diminazene diaceturate was successful in the surviving ponies.