Maintenance of Brucella abortus-free herds: a review with emphasis on the epidemiology and the problems in diagnosing brucellosis in areas of low prevalence.

This review covers some epidemiological aspects that allow Brucella to survive, spread, and maintain itself in the environment. Because the success of maintaining Brucella-free herds is determined by the efficiency of the serological tests to detect a single infected animal the limitations of the traditional serological tests are emphasized. Serological tests cannot differentiate between cattle infected with Brucella and cattle infected with microorganisms that serologically cross-react with B. abortus antigen. These cattle and cattle with 'natural' antibodies jeopardize the Brucella-free status of a herd. Likewise, infected cattle with serologically inconclusive test results or which elude detection are also a hazard to Brucella-free herds. Since cattle that elude detection with serological tests and the presence of non-specific serum antibodies in healthy cattle have long been recognized as problems, it is opportune to reconsider the procedures currently used to diagnose brucellosis in individual animals. Use of the skin delayed-type hypersensitivity test in addition to serological tests will significantly improve the diagnosis of brucellosis. This will limit the financial loss incurred by outbreaks of brucellosis.