A serologic method for the detection of Corynebacterium pseudotuberculosis infections in horses

A serologic technique useful for detecting antibodies formed in horses in response to infection with Corynebacterium pseudotuberculosis is described. The test relies on the ability of C. pseudotuberculosis toxin to produce a wide zone of hemolysis when applied to erythrocytes previously treated with a sterile filtrate of Corynebacterium equi broth culture. The synergistic hemolytic activity can be neutralized by anti-C. pseudotuberculosis serum. This test was used to analyze sera from 616 horses for the presence of C. pseudotuberculosis antitoxin. Of 177 animals (see Table 2) found positive, there were 34 horses with bacteriologically confirmed, active infections and 18 with active but unconfirmed infections. In addition, 13 animals had a history of having had the disease and 112 had no history or evidence of having had the infection. The other 439 horses had negative titers. Statistical treatments confirmed the value of the test as an epidemiological tool but precluded using only titers for the diagnosis of active clinical disease.