Preliminary evaluation of diagnostic tests using horses experimentally infected with Trypanosoma evansi

Seven surra negative horses were intravenously inoculated with 3 x 10(6) Tr ypanosoma evansi parasites derived from a camel. One horse was maintained a s an uninfected negative control. Three antigen and three antibody detectio n tests were evaluated for diagnosis of infection in horses. The microhaema tocrit centrifugation test (MHCT) was the most sensitive, first detecting p arasites between one and three days ((x) over bar 2.4) post infection (p.i. ). The antigen (ag)-ELISA detected antigen between three and ten days ((x) over bar 6.6) p.i. The latex agglutination test (LAT) first gave positive r esults on day 3 ((x) over bar 3.0) p.i. Following the treatment of horses w ith trypanocidal drugs, the MCHT and the mouse inoculation test (MIT) becam e negative. Antigen levels using LAT declined and reached pre-infection lev els in five out of six horses during the period of observation (92-279 days ). Antigen levels using the ag-ELISA declined as well but did not reach pre -infection levels in any of the six horses. Three antibody detection techniques, ab-ELISA, card agglutination test (CAT T), and immunofluorescent antibody test (IFAT) detected antibodies in the b lood of all seven infected horses but not in the uninfected control. Howeve r, the ab-ELISA did not discriminate clearly between sera from infected and uninfected horses because unacceptably high ELISA background readings were detected in 15% of the surra negative horses shipped to the UAE from the U K. The ELISA antibody increased above pre-infection levels in the six horse s experimentally infected, but not in one horse. In this horse the ELISA an tibody level exceeded the cut-off level only after the reoccurrence of the T evansi infection. The IFAT detected antibodies 15.7 days p.i. in all infe cted horses. (C) 2001 Harcourt Publishers Ltd.