INFECTION OF CATTLE WITH YERSINIA-ENTEROCOLITICA O 9 A CAUSE OF THE FALSE-POSITIVE SEROLOGICAL REACTIONS IN BOVINE BRUCELLOSIS DIAGNOSTIC-TESTS/

During the last four years, an increasing number of cattle herds were classified positive by brucellosis screening tests in areas of Belgium and France free of the disease. No clinical symptom of brucellosis wa s reported in these animals and no Brucella abortus strains were isola ted. After two years, no brucellosis outbreak was registered in all of the herds concerned. On this basis, all the serological reactions obs erved were classified as false positive. An ELISA using Yersinia Outer membrane Proteins (YOPs) as antigens was developed in order to discri minate between a Yersinia enterocolitica O:9 infection and a Brucella abortus infection. Antibodies against YOPs were detected in sera from Y. enterocolitica O:9 experimentally infected cattle (n=4) but not in sera from B. abortus experimentally infected cattle (n=4). In a field study, 66.7% of the 174 serum samples from cattle presenting false pos itive serological reactions showed anti-YOPs antibodies whereas only 1 0% of 454 sera, classified negative by the brucellosis screening tests , showed anti-YOPs antibodies, Our results suggest that infections wit h Y. enterocolitica O:9 may cause false positive reactions in brucello sis testing.