Parameter estimates to support future risk assessment of Mycobacterium bovis in raw milk cheese

Abstract

Zoonotic tuberculosis, caused by Mycobacterium bovis, is mainly linked to the consumption of raw milk from infected cows. In many countries, cases are rare, due to pasteurisation of milk and national programmes to control M. bovis infection in cattle. Speciality cheeses, which are often produced using raw milk, present challenges to risk managers in countries where M. bovis is endemic or (re-) emerging. A key concern is the potential risk of zoonotic transmission of M. bovis via the consumption of dairy products produced using raw milk originating from herds infected with M. bovis (bovine tuberculosis, bTB). The aim of this study was to determine parameter estimates to support the future risk assessment of M. bovis in raw milk cheese. In this study, the hazard was identified as viable M. bovis organisms in raw milk cheese. Parameters of interest in this study related to exposure assessment (the estimated extent of human exposure to viable M. bovis organisms) and hazard characterisation (the risk posed to human health following exposure to viable M. bovis organisms). The pathway for exposure assessment was visualised using a conceptual framework, which describes the steps through which M. bovis may be transferred from an infected animal(s) through manufacturing to the final cheese product. Estimation of most parameters for exposure assessment and hazard characterisation was undertaken using systematic literature reviews. Estimates could be derived for many parameters, but not all. In particular, the number of M. bovis organisms excreted in the milk and present in the faeces of infected cattle are unknown. There is zero-tolerance for M. bovis in foods of animal origin destined for human consumption in European legislation. This work has highlighted important gaps in knowledge, and areas for further research. For each of the parameters for which estimates are available, we outline the types/sources of uncertainty as reflected in relevant published papers. In any future application of these parameter estimates, care will be needed to reflect the uncertainties associated with these elements of exposure assessment.