Comparison between a soluble antigen-based ELISA and IFAT in detecting antibodies against Babesia canis in dogs

An available enzyme-linked immunosorbent assay (ELISA) was studied for the detection of anti-B. canis antibodies in the sera of dogs using, indirect fluorescent antibody test (IFAT) as a reference test. ELISA uses a soluble antigenic preparation of B. canis and the optimal dilutions of the antigen, serum and conjugate were determined by check board titration, using positive and negative reference serum. The soluble antigen preparation of B. canis merozoites was 10 microg x mL(-1), with reference sera from positive and negative in a single dilution of 1:100, and conjugated to 1:4.000. A total of 246 serum samples were collected from dogs during the rabies vaccination campaign in Jaboticabal, São Paulo, Brazil and examined for the presence of antibodies against B. canis by ELISA and IFAT. Under these conditions, the average absorbance of negative serum was 0.129 + or - 0.025, resulting in a cut-of value of 0.323 (ELISA level 3) and the average absorbance of positive reference serum was 2.156 + or - 1.187. The serological positive samples tested for B. canis by ELISA and IFAT were 67.89% (n = 167) and 59.35% (n = 146), respectively. These results suggest that ELISA described may prove to be an effective serological test to diagnose canine babesiosis.