Latent carriers of brucellosis.

Of 272 heifers subjected to a brucellosis anamnestic test following one injection of K45/20A vaccine, 53 (19%) gave a positive result to the anti-bovine globulin test and 21 (8%) gave a complement fixation test titre at 1/16 or more. Three heifers (1%) gave a positive serum agglutination test (SAT) titre (60 iu or more) 12 weeks after the second injection of K45/20A vaccine. One of the three aborted at seven months' gestation (Brucella abortus culture positive), another had an SAT level of 100 iu 10 days after calving while the SAT titre of the third heifer continued to fall and remain negative after a normal calving. All the remaining heifers continued to give negative SAT. Recommendations are made for interpreting the anamnestic test for the diagnosis of the latent carrier state.