FALSE-POSITIVE SEROLOGICAL REACTIONS IN BOVINE BRUCELLOSIS - EVIDENCEOF THE ROLE OF YERSINIA-ENTEROCOLITICA SEROTYPE O-9 IN A FIELD TRIAL

To investigate the epidemiology of false positive serological reaction s (FPSR) in bovine brucellosis, 1 259 bovines from 20 herds were sampl ed on three successive occasions during the winter of 1993-1994 in an area where the herd prevalence rate of FPSR was high. Serum samples we re examined by classical brucellosis serological tests (Rose Bengal an d complement fixation) and faeces were cultured for the presence of Ye rsinia enterocolitica O:9. Thirty-nine bovines expressed at least one positive serological reaction during the study. In the herds with FPSR during the 1993-1994 annual brucellosis surveillance campaign, the sp ecificity of the brucellosis serological tests varied significantly fr om December to March (97.0% to 99.1%). Y enterocolitica O:9 was isolat ed from 42 bovines but only three of them showed a positive serologica l response during the study. Y enterocolitica O:9 isolation rates also decreased with time. Young animals and animals having demonstrated FP SR in the past had a greater risk of having a FPSR. Older animals, whi ch rarely showed FPSR, could form a reservoir for Y enterocolitica O:9 . While isolation of Y enterocolitica O:9 was not linked to presence o f FPSR and conversely, the FPSR phenomenon should be considered, eithe r at the herd level or at the individual level. This work reinforces t he link, at least partial, between FPSR and infection by Y enterocolit ica O:9.