Team:Exeter/BovineTB
Bovine TB
TB in cattle is caused by Mycobacterium bovis, which is just one of several members within the Mycobacterium tuberculosis group. Bovine tuberculosis is a zoonotic disease with the potential to transmit infection between animals and humans. Transmission to humans usually occurs via infected milk, however, in developed countries where milk pasteurisation is routine, most bacteria within infected milk is killed meaning actual infections in humans are rare within these areas. Conversely, in areas of the developing world M. bovis is a relatively common cause of human tuberculosis. bTB is a disease which affects a broad range of mammalian hosts. In addition to humans and cattle, it can also cause disease within deer, llamas, pigs, foxes and possum, just to name a few. Depending on the species involved, spread of infection can occurr via direct contact, contact with the excrement of an infected animal, or inhalation of even one aerosol droplet. Importantly, high rates of infection have been found in Eurasian badgers (Meles meles) (Proud and Davis, 1998) and the general consensus between scientists with the TB community is that badgers are a significant source of TB in cattle (Clifton-Hadley et al., 1995; Denny and Wilesmith, 1999; Eves, 1999; Martin et al., 1997; Martin et al., 1998). Badgers in particular are a topic of controversy, causing discrepancy between farmers, vets, politicians and activist groups.
Badger-Cattle transmission
Badgers have been implicated as a potential source of M. bovis for cattle since an infected badger was identified in GB in 1971. Since then, there has been evidence published which supports a role for infectious badgers in bTB epidemiology. Some observations that have been made include:
- The routes of transmission proposed between badgers and cattle, predominantly direct aerosol infection, are plausible given the current understanding of the badger-cattle interface
- Molecular typing data supports a local epidemiological association between M. bovis in cattle and badgers. Badgers and cattle tend to share the same M. bovis genotype in the same area. This is was evident in GB data obtained during the Randomised Badger Culling Trial as well as within trials in other areas including Northern Ireland (NI) and the Republic of Ireland.
- Badger culling trials conducted in GB and the ROI demonstrated indirectly that badgers contribute to the prevalence of TB in cattle. However, even with these large scale, expensive trials it has not been possible, and may not be possible to accurately quantify the extent of transmission between badgers and cattle, or vice versa.
Furthermore, it has been noted that there appears to be a relationship between the type of landscape (e.g. Southwest England) and the risk posed by badgers (White et al., 1993). The preferred badger habitat in the UK is well-drained soil close to deciduous and mixed woodland (Clements et at., 1988), bordering large areas of grassland (Wilson et al.,1997). When you take into account the fact that this is the type landscape most favoured in the UK for cattle grazing, it is no surprise that badgers, which are natural reservoir of M. bovis, would be suspected of transmission to cattle.
Badger protection
Although European badgers are not an endangered species, they are among the most legally protected wild animals in the UK. Due to the implementation of Protection of Badgers Act 1992, as wells as the Wildlife and Countryside Act 1981, and the Convention on the Conservation of European Willife and Natural Habitats, badgers are thoroughly shielded by the government, and badger culling is banned.
What Can We Do?
As part of our human practices we, as a team, have made every effort to tailor our test to the people who will be using the final product. By looking at the TB debate from different perspectives, we were able to make sure that we developed a test that catered to the both the local farmers and the local veterinary community while taking into account the ethical implications that were brought to our attention by environmental activists.