TB in the Environment

 

Persistence of M. bovis in the environment

Bovine tuberculosis (bTB) is a chronic, infectious disease caused by the slow-growing bacterium, Mycobacterium bovis (M. bovis). It is mainly a disease of cattle and other bovines, but can affect a wide range of species. Once infected, the opportunity to transmit the disease varies between species.

In parts of the UK, there is a recognised reservoir of infection in badgers, with transmission occurring between cattle, between badgers and between the two species. Compared with badgers, wild deer are likely to play a secondary role in the perpetuation of TB in British cattle and research suggests this occurs only in localised areas at high deer population densities.

Primarily a respiratory disease, transmission of bTB normally occurs directly through close contact by breathing in droplets of sputum containing M. bovis exhaled from an infectious animal. Research suggests that M. bovis bacteria can survive in aerosol form for a few hours after exhalation.

However, the infection may also be transmitted indirectly, through contact with material (or ingestion of feed) heavily contaminated with M. bovis that may be shed in the sputum, pus, urine, faeces and other excretions of infectious animals. There are practical difficulties with the detection of M. bovis in environmental samples. Nevertheless, the bacterium has been identified in a wide range of sources including soil, faeces, slurry, hay and pasture.

After excretion, M. bovis may remain viable (although it cannot multiply) in the environment for a variable period of time, which can range from a few days to many months depending on the weather and other environmental conditions.

The ultraviolet rays in sunlight have been shown to inactivate M. bovis within hours, although the organism may remain viable for several weeks on pasture.

Inactivation is likely to take longer during winter months, as M. bovis survives best in cool, moist environments shaded from direct sunlight.

Studies conducted in Ireland have shown that M. bovis can persist in slurry for up to six months and spreading slurry after storage for less than two months has been associated with an increased risk of bTB.

Factsheets

For more information about survival of M. bovis in the environment, see the following factsheets.

 

Useful links

 

Please see the following links for more detailed information on the persistence of M. bovis in the environment.

> Click here for DARDNI Review of Badger-to-Cattle Transmission. Allen AR, Skuce RA, McDowell SWJ (2011). Bovine TB: a review of badger-to-cattle transmission

> Click here for DARDNI Review of Cattle-to-Cattle Transmission. Skuce RA, Allen AR, McDowell SWJ (2011). Bovine TB: a review of cattle-to-cattle transmission, risk factors and susceptibility

> Click here for DARDNI Slurry Literature Review. McCallab L, McNair J, Skuce RA (2014). A review of the potential role of cattle slurry in the spread of bovine tuberculosis

> Click here for Veterinary Medicine International Research. Fine AE, Bolin CA, Gardiner JC, Kaneene JB (2011). Study of the Persistence of Mycobacterium bovis in the Environment under Natural Weather Conditions in Michigan, USA