Why do badgers have tb

From our point of view, it's the most important bacterial disease that afflicts us, causing about one-and-a-half million deaths a year. This is how TB is caught: you breathe in tiny droplets of fluid containing just a few bacilli. In your lungs, your own immune cells move in and swallow up the bugs — but this is exactly what they want.

Inside the immune cell, the bacilli replicate and pile up. More immune cells pile in. If you're lucky, the bacilli are held tight in this lump, this tubercle. If you're unlucky, the bugs get out and the disease spreads — through your lungs and you start coughing up droplets with bacilli in, ready to infect someone else , through your whole body, even getting into your bones. Not that long ago, TB in humans was thought to have been a fairly recent affliction, dating back to the neolithic and the origins of farming.

This oft-repeated idea seemed reasonable — there didn't seem to be any convincing cases of TB in skeletons dating to earlier periods. Perhaps close contact between early farmers and their cattle exposed them to M bovis , which then evolved into M tuberculosis in its new host.

But this isn't the story written in the DNA of the bacilli. In , an early genetic study cast doubt on the ancestor-descendant relationship between the bovine and human forms of TB. More studies confirmed the new story. If anything, the ancestor of both human and bovine forms must have been closer to the human form — with its larger chromosome.

It's even possible that cows caught TB from us or at least, from another mammal that had caught "human" TB. Using molecular clocks to date the age of M tuberculosis , looking for the last common ancestor of current versions of the bug, is problematic, and has produced a great range of dates from , years ago.

All of these easily predate farming. However, this date is likely to just record a population crash in TB, probably because of a crash in the numbers of its host. They combined this with detailed information on where the cattle and badgers lived, when they were infected, and whether they could have had contact with one another. Scientists were then able to estimate how often the two species spread TB.

They found that badgers play an important role in the transmission of the disease in this area. In October, peer-reviewed, scientific evidence highlighted the effectiveness of badger culling in reducing outbreaks of bovine TB in cattle.

Prof Christl Donnelly, from University of Oxford and Imperial College London, who led the Downs et al study, said the latest paper provides an interesting and important new perspective on the challenging problem of bovine TB in cattle and badgers. Sign in. Scientists say the changes were witnessed as soon as culling began, meaning even badgers that were killed may have first spread the infection over wider areas while the scheme was being implemented.

However, the animals spent less time outside of their setts in culled areas — on average, 91 minutes less per night. Researchers believe this could be linked to reduced competition and increased food availability as badgers are removed from the population.

Separate research published in March also suggested culling badgers spreads TB. It found that culls disrupt local populations and drive them into previously uninfected areas.

Last year the government commissioned a review of its strategy for tackling bovine tuberculosis in livestock amid ongoing controversy about badger culling to control the disease.