Non specific serological reactions in the diagnosis of bovine brucellosis: experimental oral infection of cattle with repeated doses of Yersinia enterocolitica O:9

Abstract

Eight heifers were orally infected with 4 × 10 9 colony forming units of a field cattle strain of Yersinia enterocolitica O:9 in a capsule, 5 days a week, for about 9 weeks (day 0–day 64 (D0–D64)). The faecal shedding of Y. enterocolitica O:9 began on D5 for seven out of the eight challenged cattle with a high level of excretion during the first month, followed by a decrease till the day of slaughter (D76). Y. enterocolitica O:9 was not isolated from organs collected at slaughter. No clinical symptoms were observed. Hyperplasia of intestinal lymph formations was the sole microscopic lesions observed. Five animals showed a serological reaction against Brucella antigens in at least one of the following tests: Rose-Bengal test, complement fixation test, tube agglutination test or indirect ELISA (iELISA) tests. Only one animal showed a high level of serological response and a positive reaction in the dithiothreitol-microagglutination test. The observed variability in terms of individual sensitivity to the Y. enterocolitica O:9 infection is in agreement with the low individual prevalence rate and the transient serological reaction and faecal Y. enterocolitica O:9 shedding observed in herds showing false positive serological reactions in brucellosis.