Investigations of adult sheep vaccinated with Gudair® for protection against ovine Johne’s disease.

Abstract

This observational study closely examined the gross and histopathological lesions associated with ovine Johne’s disease in sheep vaccinated as adults with Gudair®. Two cohorts of Gudair® vaccinated sheep were used from two separate properties both with high OJD mortality rates (>5%). All sheep had been vaccinated outside the recommended 1 to 4 months of age, mostly as adults. Vaccination injection site lesions were prevalent (>39%) in both cohorts of sheep at least 6 months post vaccination. At necropsy, lymphatic cording was found to be a good indicator of OJD and highly correlated with the formation of a multibacillary lesion. This study indicates the possibility for misdiagnosis of OJD based on gross pathology alone and emphasises the necessity for histological confirmation. Histopathology from the two cohorts of sheep reports a high proportion of multibacillary lesions in one group and a predominance of paucibacillary lesions in the other. This suggest the use of the Gudair vaccine could effect the type of histological lesion developed in OJD infected sheep vaccinated as adults, however further research is necessary to identify additional property factors which could be involved.