Exposure Assessment for Mycobacterium avium subspecies paratuberculosis

Summary

Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s Disease in cattle, sheep and other ruminant species. Growing speculation about the role of MAP in the pathogenesis of Crohn's Disease has provoked interest in reducing the exposure of humans to MAP. The aim of this project was to assess the likelihood of exposure of humans to MAP through the consumption of red meat and to identify possible mitigation strategies to minimize this exposure. This quantitative exposure assessment identified the potential pathways of exposure, focusing on direct consignments from beef and dairy cattle and sheep properties and estimated the amount of MAP present in muscle, liver and intestines at the end of the abattoir slaughter line. A combination of peer-reviewed literature, industry reports, unpublished studies and expert opinion were used to populate the models. Results from these assessments indicate that most animals entering the slaughter line are non-infected animals from non-infected flocks/herds. Of animals coming from infected flocks/herds, most animals are non-infected with only low level MAP on the carcass surface due to cross-contamination; with an extremely low proportion of infected animals with high level of MAP present on the carcass surface. Adult sheep from high prevalence areas and dairy cattle from management areas are the animals posing the highest probability of exposure. The most influential parameters on the probability of exposure to and the amount of MAP present in product are (1) whether sheep flocks are vaccinated against Johne’s disease and (2) the quantity of faeces present on the carcass surface of sheep and cattle. The study suggests that it is possible for MAP to be present in red meat products. However; the risk of human exposure through the red meat chain in Australia is low.