Evaluation of agar gel immunodiffusion and indirect fluorescent antibody assays as supplemental tests for dourine in equids.

The agar gel immunodiffusion (AGID) and indirect fluorescent antibody (IFA) assays were evaluated as supplemental tests to the complement-fixation (CF) test, the official US importation certification test for dourine in equids. The American stabilate (n = 10 animals) or the Canadian stabilate (n = 6 animals) of Trypanosoma equiperdum cultured in rat blood was administered by catheterization and infusion in the urogenital tract of 16 equids. To assess parasitemia and serologic responses by use of the CF, AGID, and IFA tests, a total of 787 serum and blood samples were obtained from equids before exposure and 3 times a week after exposure to T equiperdum. Results of the IFA and AGID tests were compared with the CF test results. The disease was diagnosed earlier by the IFA test than by the AGID test, regardless of antigen preparation or exposure group. The mean number of days between exposure and positive result by the CF and IFA tests was the same when either homologous or heterologous antigen was used in the IFA test. In general, the IFA test was more sensitive than the AGID test in diagnosing dourine, regardless of the antigen preparation used in the test or exposure group. Differences in test specificity were observed among both groups of exposed equids when either antigen was used (P < 0.05). The AGID test, using the American antigen, was more specific than the IFA test for sera from both groups of equids. When the Canadian antigen was used, the IFA test was a more specific test than the AGID test (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)