Evaluation of the indirect fluorescent antibody test for detecting Trypanosoma vivax in South American cattle.

The indirect fluorescent antibody test (IFAT) as used in Africa for detecting bovine trypanosomiasis was adapted for use in South America and evaluated. Antigen consisted of Trypanosoma vivax laden bovine blood fixed in a 60 : 40 : : acetone : methanol solution. The test detected initial titres of 1 : 50 and 1 : 100 at an average of 13.1 and 15.9 days post parasitaemia (PP). Maximum titres as high as 1 : 400 developed in eight calves at an average of 23.4 days PP. In another calf, 109 days PP were required. Efficacy in detecting sero-positive calves throughout the course of infection was 81.1 and 96.4 per cent at serum dilutions of 1 : 100 and 1 : 50 respectively. No false positive reactions occurred when sera from 36 haemoparasite-free calves were tested. Cross reactivity did not occur when sera from calves singularly infected with Trypanosoma theileri, T evansi, Anaplasma marginale, Babesia argentina, B bigemina and Eperythrozoon spp were similarly tested in the IFAT. No significant differences were found in IFAT results of surveys in which both conventional serum samples and sera eluted from dried blood samples on filter paper from the same calf were used.