Assessment of an intradermal test for the detection of bovine brucellosis.

Forty-eight cattle were sensitised to Brucella antigens either by vaccination with Brucella abortus strain 19 (S19) or B. abortus 45/20 (S45/20) ad 24 of these and 12 unvaccinated cattle were subsequently challenged with virulent B. abortus strain 544 (S544). All these cattle (n = 60), together with 12 control cattle which were neither vaccinated nor challenged, were subsequently subjected to an intradermal test using a S45/20 protein antigen. Reactions were interpreted subjectively by observation and palpation and were measured to the nearest mm with calipers at 48 and 72 hours after injection of protein antigen. Ten weeks later the cattle were slaughtered and tissues cultured for the presence of B. abortus. Two of the 48 vaccinated cattle died, 40 of the remaining 46 gave a positive response to the intradermal test at 48 hours and 36 were positive at 72 hours. In the controls any increase in the skin thickness had disappeared by 72 hours. An increase in skin thickness was still present at 72 hours in all other cattle except those vaccinated with S19 only. The intradermal test was found to be sensitive but not specific in detecting infected cattle and both sensitive and highly specific if used (with the exception of S19) to detect exposure to Brucella antigen.