A haemolysis inhibition test for detection of antibody to Corynebacterium ovis exotoxin.

A haemolysis inhibition test for detection of antibody to Corynebacterium ovis exotoxin is described. The basis of the test is te inhibition, by immune serum, of the haemolytic activity of C ovis exotoxin for sheep red cells. When the test was applied to sera from sheep which had been vaccinated with C ovis cells and exotoxin, the geometric mean titre increased from < 2 to 137 whereas in sheep vaccinated with C ovis cells only, the mean titre remained < 2. Experimental infection with a toxigenic C ovis strain produced titres ranging from 2 to 32 in 10 out of 12 sheep but a nontoxigenic C ovis strain did not produce a response in any of six sheep. The test was successful in diagnosing 24 out of 30 sheep with caseous lymphadenitis evident at autopsy. Antitoxin was also detected in the serum of six out of seven lambs suckled by ewes which had positive titres.