Evaluation of antigen detection and antibody detection tests for Trypanosoma evansi infections of buffaloes in Indonesia

Two Ag-ELISAs, an IgG-specific antibody detection ELISA (IgG ELISA) and a c ard agglutination test (CATT) for the detection of Trypanasoma evansi infec tions in buffaloes in Indonesia, were compared. Diagnostic sensitivity esti mates were obtained by testing sera from 139 Indonesian buffaloes which had been found to be infected by parasitological tests. Diagnostic specificity was estimated by testing sera from 263 buffaloes living in Australia. Resp onse-operating characteristic curves were constructed, and optimal ELISA cu t-off values, which minimized the number of false-negative and false-positi ve results, were chosen. The IgG ELISA had the highest sensitivity (89 %) a nd the CATT had the highest specificity (100 %). There was a significant di fference between the sensitivities (71 and 81%), but not between the specif icities (75 and 78 %), of the two Ag-ELISAs. The four tests were further co mpared by calculation of post-test probabilities of infection for positive and negative test results using a range of prevalence values, and likelihoo d ratios. The results suggested that the CATT was the best test to 'rule-in ' infection (i.e. the highest probability of infection in test-positive ani mals) and the IgG ELISA was the best test to 'rule-out' infection (i.e. the lowest probability of infection in test-negative animals).