Studies of infectivity and pathogenicity of an isolate of Trypanosoma evansi in Yankasa sheep

The course of experimental infection and pathogenicity of an isolate of Try panosoma evansi were investigated using eight infected and six uninfected c ontrol Yankasa sheep. The sheep were each infected intravenously via the ju gular vein with approximately 2.0 x 10(6) T. evansi parasites. The effects of the parasite on body temperature, packed cell. volume (PCV), haemoglobin , erythrocytes, total protein, were monitored three times a week for approx imately 9 weeks. Body weights were determined once every week for the durat ion of the experiment. The results showed that all the infected sheep were positive for the parasite. The prepatent period varied between 3 and 6 days . I: evansi produced parasitaemic waves at an average of 8.3 days interval. Two distinct forms of the disease were produced namely, acute (4-14 days p ostinfection), and chronic (43-59 days postinfection). Anaemia was a distin ct feature of the disease. While the mean rectal temperatures were significantly elevated (P < 0.05), the mean values of the haematological parameters of the infected sheep drop ped significantly (P < 0.05) compared to the preinfection levels. Observed clinical signs included pale mucous membrane, epiphora, loss of appetite, e maciation, dullness and rough hair coat together with fluctuating pyrexia w hich in most cases coincided with rise in parasitaemia. It is suggested tha t the isolate of I: evansi is pathogenic for Yankasa sheep. (C)1999 Elsevie r Science B.V. All rights reserved.