Reservoirs of bovine TB in wildlife and livestock: an environmental perspective

Abstract

Infections caused by mycobacteria are global and represent an important veterinary and public health problem. A critical component in controlling transmission is the identification of wildlife reservoirs. We have identified the environment as a further potential component of the M. tuberculosis complex transmission cycle. Once outside the enriched mammalian host (or culture media), cells are likely to be in an altered physiological state, as pathogens can enter a resilient but quiescent state in order to survive the biotic and abiotic stresses of the environment. Culture independent methods are required to quantify these cells, and culture dependant methods have been relied on to establish if they are viable and potentially capable of causing infection.

Bovine tuberculosis (bTB) caused by Mycobacterium bovis is a persistent problem in cattle herds in Great Britain and Ireland and controlling disease spread through UK cattle herds is a significant challenge as the Eurasian badger (Meles meles) has been highlighted as a wildlife reservoir that may be a significant source of continued re-infection. Determining the disease prevalence and TB status of badger populations is a challenge and currently requires direct interaction with individual animals through expensive and labour intensive trapping and testing regimes. Whilst the involvement of badgers in the transmission cycle of M. bovis is well established, the route of transmission from wildlife to cattle and vice versa is not understood sufficiently to inform day-to-day management of transmission risks on the farm.

We have developed a qPCR based non-invasive test which avoids handling of badgers and can highlight social groups which shed M. bovis into the environment with an indication of M. bovis faecal load. Data on faecal shedding provided a reliable proxy for tracheal shedding and was used to monitor the infectiousness of social groups of animals. The further application of highly sensitive techniques for molecular epidemiology has advanced our ability to study populations remotely and enabled the evaluation of disease burden, transmission and impact of interventions (such as vaccination of badgers) on the disease status in a given population. Many infectious diseases involve shedding (through sputum, faeces and/or urine) which is an indicator of disease burden.   

Host: Professor Michael Brockhurst