Brucella Agglutinin-blocking Phenomenon in Bovine Sera

Abstract

Sera of a total of 88 cows from 5 herds were tested for Brucella agglutinin by tube-agglutination titer, and rapid macroscopic agglutination titer against a culture of B. abortus Brucella-agglutinin-blocking activity of sera was measured by adding 0.1 ml. of a known complete B. abortus rabbit antibody, in such dilution as to produce agglutination of antigen in control tubes to which no bovine serum had been added, to tubes containing bovine serum and antigen. Two of the herds were considered clinically free of brucellosis; sera of the 36 animals in these herds showed no agglutinin-blocking activity, and with the exception of a single animal which had been vaccinated against brucellosis, none showed a tube-agglutination or rapid macroscopic titer greater than 1:40. The remaining 52 animals came from 3 herds considered clinically suspicious of harboring Brucella-infected animals; of these 24 sera showed tube-agglutination titers greater than 1:40, 35 showed rapid macroscopic titers of greater than 1:40, and 35 showed agglutinin-blocking activity. In 9 of the sera which showed diagnostically insignificant titers by tube-agglutination there was a high rapid macroscopic titer and considerable agglutinin-blocking activity. Thus, the rapid macroscopic agglutinin titer is a more reliable index of the presence of Brucella agglutinin than the tube-agglutination test, since agglutinin blocking activity does not seriously interfere with the former test.