The ID Screen® Brucella suis Indirect ELISA is a valuable supplement for serological diagnosis of porcine brucellosis.

Brucellosis in domestic pigs, mainly caused by Brucella (B.) suis, has been eradicated in many European countries and the domestic pig population is monitored for freedom of disease by serological methods. However, antibodies cross-reacting with the prescribed smooth lipopolysaccharide (sLPS) diagnostic antigen, might lead to false positive serological results (FPSRs) due to antigen similarity with other bacteria, such as Yersinia species. Domestic pigs are frequently colonised with Y. enterocolitica. The ID Screen® Brucella suis Indirect ELISA, based on sLPS and rough LPS (rLPS) was developed to confirm FPSRs in porcine sera. The performance of the ID Screen® Brucella suis Indirect ELISA was analysed using 143 field sera from domestic pigs with different brucellosis status: group 1: brucellosis-free pigs kept in an artificial insemination unit (n=65); group 2: brucellosis-free herds showing seropositivity for brucellosis in different sLPS-based serological tests, suspected to be FPSRs (n=53); group 3: herds with confirmed porcine brucellosis (n=25). Additionally, sera were tested with Pigtype® Yersinia Ab ELISA. Sera of group 1 were confirmed as truly serological negative for brucellosis with the ID Screen® Brucella suis Indirect ELISA. In group 2, 51 out of 53 sera (96 %) were confirmed as FPSRs by the ID Screen® Brucella suis Indirect ELISA. Nineteen sera (76 %) of group 3 tested truly serological positive for brucellosis. The results confirm the good discriminatory power of the ID Screen® Brucella suis Indirect ELISA for false serological brucellosis positivity. Moreover, our data confirmed that cross-reactive Yersinia antibodies are the most likely cause of FPSRs.