Comparison of antibody- and antigen-detection enzyme immunoassays for the diagnosis of Trypanosoma evansi infections in camels.

A total of 183 camels from Kenya were examined for circulating trypanosomal antigens by four methods: (1) a monoclonal antigen-detection enzyme-linked immunosorbent assay (Ag-ELISA) and circulating anti-trypanosomal antibodies; (2) antibody-detection enzyme-linked immunosorbent assay (Ab-ELISA); (3) buffy-coat examination (BCE); (4) mouse subinoculation (MI). Thirty-seven camels (20%) were parasite-positive by BCE and 60 camels (33%) were parasite-positive by MI. Sixty-three camels (34%) tested positive on Ag-ELISA. Of the 24 camels which could not be detected by BCE, Ag-ELISA detected 18 (75%). Ab-ELISA detected 90 (49%) positive camels. Of all the parasite-positive camels (61), Ag-ELISA detected 93% and Ab-ELISA 95%. Based on the results of 55 camels, there was a significant statistical difference (P < 0.0001) in Ag-ELISA optical density (OD) values (of either serum or plasma antigen analysis) between parasite-positive and parasite-negative camels. No significant difference was observed in Ab-ELISA OD values between parasite-positive and parasite-negative camels. Diagnosis of T. evansi infection in camels by the use of Ag-ELISA alone or in combination with BCE could therefore be a more preferred approach in assessing patient infection than the use of Ab-ELISA.