Differentiation between serological responses to Brucella suis and Yersinia enterocolitica serotype O : 9 after natural or experimental infection in pigs

False-positive serological reactions (FPSR) due to infections with Yersinia enterocolitica serotype 0: 9 (YeO:9) are a problem in tests for brucellosis. In the present study, FPSR in classical and novel tests for brucellosis following experimental infections of pigs with YeO:9 were compared with responses of B. suis biovar 2-inoculated pigs. FPSR were limited to 2-9 weeks post-YeO:9 inoculation, while B. suis-infected pigs were test-positive throughout the 21-week period of investigation. Although YeO:9-inoculated pigs exhibited FPSR in Brucella tests for a limited period of time, the serological responses in a YeO:9-purified O-antigen indirect ELISA did not decrease accordingly. Analysis of available cross-sectional serum samples from pig herds naturally infected with YeO: 9 or B. suis biovar 2 confirmed that the observed difference in the duration of the serological responses between the two infections could be used to discriminate between herds infected with B. suis biovar 2 and YeO:9.