EVALUATION OF AN ELISA FOR DETECTION OF ANTIBODIES TO BABESIA-BOVIS IN CATTLE IN AUSTRALIA AND ZIMBABWE

An enzyme-linked immunosorbent assay (ELISA) for antibodies to Babesia bovis was evaluated in comparison with the indirect fluorescent antib ody test (IFAT) in Australia and Zimbabwe. Positive and negative thres hold values for the ELISA were set using sera from cattle of known inf ection status. Sensitivity and specificity estimates for the ELISA bas ed on 158 positive sera from cattle experimentally infected with Austr alian isolates of B. bovis and 318 negative sera collected from B. bov is-free herds in Australia were 100% and 99.4%, respectively. The spec ificity of the assay in Africa, based on 328 sera from B. bovis-free h erds in Kenya and South Africa, was 99.7%. The ELISA was compared with the IFAT using sequential sera from 16 calves experiencing primary B. bovis infections, and a total of 777 field sera collected from B. bov is-endemic herds in Australia and Zimbabwe. In primary infections, the ELISA and IFAT detected antibodies at or about the same time. With se ra from endemic herds, the performance of the ELISA was at least compa rable with that of the IFAT. Two hundred and fourteen of 221 sera that were negative by IFAT, were negative by ELISA, and 428 of 439 sera th at were clearly positive by IFAT were positive by ELISA. Of 117 sera t hat gave equivocal (suspect or weak positive) results in the IFAT, 20 were positive by ELISA, 7 were suspect and 90 were negative. We conclu de that the ELISA will be useful for epidemiological studies on B. bov is in Australia and Zimbabwe, and probably elsewhere. (C) 1998 Elsevie r Science B.V.