Serums collected from Illinois veterinarians at 6 state conventions between 1956 and 1972 were tested for Brucella
antibodies, with 70 of 394 (17.8%) samples reactive. Interviews with 1,261 veterinarians in 1967 and 1968 yielded 175 (13.9%) with a history of a prior clinical illness diagnosed as
brucellosis. When duplicates were eliminated, there was a 17.0% (224/1,315)
infection ratio. The prevalence of
infection was found to be decreasing, as reflected by decreasing serologic reactor rates and by decreasing numbers of clinical diagnoses during the period. Strain 19
brucella vaccine appeared to be increasing in relative importance as a source of
infection for veterinarians. Most of the small animal practitioners with a history of clinical
brucellosis had been infected either as students or in an earlier practice type. Onset of clinical illness occurred the year of graduation for 21 (13%) veterinarians, with 62% between 4 years before and 4 years after graduation. Part of the explanation for the decreasing
infection rates following graduation might have been the existence of a group of veterinarians at high risk of
infection because of personal habits. Early
infection, because of their high risk, would have resulted in rapid depletion of susceptible individuals from this group. As a result, in a few years the
infection rate of the total veterinary population would no longer be dominated by this high risk group but would more nearly reflect the
infection probability for the average veterinarian. There was no significant difference in death rates or cause of death between infected and noninfected veterinarians.