Chemotherapy of surra in horses and mules with diminazene aceturate

During June-July 2000, an outbreak of surra occurred on an equine breeding farm in Khonkaen Province, Thailand. Forty-two percent of pregnant mares aborted or gave stillbirth and 40% (19/47) of horses and 10% (1/10) of mules died from surra. In August 2000 Trypanosoma evansi were detected in the remaining animals (28 horses and nine mules) on the farm by blood smear and/or the haematocrit centrifuge technique. All animals were treated with diminazene aceturate at 3.5 mg/kg body weight by intramuscular injection on days 0 and 41 of the study. Blood samples of eight randomly selected horses and mules were collected on days 0, 1 and once a week until day 56 and examined for T. evansi by various parasitological techniques. The sera were tested for antibodies against T. evansi using an indirect enzyme linked immunosorbent assay (ELISA).The results revealed that diminazene aceturate at 3.5 mg/kg appeared to be effective in the first treatment of horses and mules infected with T. evansi. Parasites were cleared from the peripheral blood of horses on days 1 and 7 and mules on days 1 and 14. Thereafter the number of positive animals increased. After the second treatment, 50% of horses and 25% of mules were still positive to surra 24 h after treatment demonstrating that diminazene had no protective effect. Mild to severe toxicity of diminazene was seen in the horses and mules after injection.