Human exposure to Mycobacterium paratuberculosis via pasteurised milk: a modelling approach

Paratuberculosis is a disease of cattle caused by infection with Mycobacterium paratuberculosis, and it has been suggested that this bacterium may also play a role in the aetiology of Crohn's disease in humans. M paratuberculosis is shed in the milk and may be able to survive pasteurisation. Therefore, people may be exposed to it by the consumption of pasteurised milk. The risk of such exposure has been analysed using a modelling approach and the model has been used to evaluate the effects of intervention measures at different points in the potential route of transmission. On the basis of data from the literature and expert opinion, an initial point estimate of the exposure level of about 0-5 cfu/litre pasteurised milk was derived, mainly due to milk from clinically affected animals. The model indicates the need for quantitative data on variations in the shedding rates of M paratuberculosis in faeces and milk, and the levels of faecal contamination of milk. Such data are essential for a proper analysis of potential exposure, and may result in a 100-fold increase in the estimated median level of exposure.