The antibody response to Brucella: immunoglobulin response measured by enzyme-linked immunosorbent assay and conventional tests.

An enzyme-linked immunosorbent assay was adapted to measure total and individual classes of brucella antibody. The results were compared with those of conventional tests for brucella antibody on the sera of a number of healthy seropositive abattoir workers and several patients with either acute or suspected chronic brucellosis. IgG was the class of brucella specific immunoglobulin most commonly detected in all groups. IgM was present in the sera of 40% of seropositive abattoir workers, all but one of the patients with recent acute brucellosis or seroconversion and none of those with suspected chronic brucellosis. Many of the abattoir workers' sera which contained brucella specific IgM gave negative results in the direct agglutination test. The presence of brucella specific IgM in the sera of these men was, in most cases, associated with no past history of acute brucellosis and a relatively short period of employment in the abattoir. It is suggested that the presence of brucella specific IgM in the serum of a person occupationally exposed to B. abortus, probably indicates a relatively recent primary infection, either symptomatic or subclinical and has no prognostic significance. Repeated or prolonged exposure is associated with IgG brucella antibodies, often in high titre, irrespective of symptoms. It was not possible, on the basis of any serological tests performed in this study to distinguish healthy people exposed to brucella from those with symptoms consistent with chronic brucellosis.