Bovine TB myth #1

Those who call for badgers to be culled to eradicate bovine TB (bTB) in cattle regularly justify their demands with a number of endlessly repeated arguments which are, to be frank, complete and utter tosh. These myths, as I will call them, need to be exposed for what they are, and I will start with the myth that bTB poses a significant welfare problem for badgers.

This particular bit of nonsense is especially topical at the moment as this month saw the following quote attributed to Defra’s Farming Minister Jim Fitzpatrick, as part of an interview about the bTB problem published by Farmer’s Guardian [1]: “What I had perhaps not recognised before is the pain and suffering being inflicted on the badger population. They are dying in numbers. This is almost an issue for their welfare and survival as much as it is for dairy herds.”

The Badger Trust has quite rightly taken issue with this statement and written to the Minister to provide the facts. In its letter the charity said: “We know of no scientific evidence or authoritative validation for a statement of that kind, though we are, of course, aware that similar but totally unsubstantiated claims have been made repeatedly by pro-cull lobbies in an attempt to emotionally influence the public to support their case.” [2]

So what are the facts – to what extent is bTB actually affecting badger welfare and survival? In a nutshell, while those badgers which actually die from bTB certainly suffer (they are usually emaciated when found [3]), bTB only causes the death of a small proportion of the badger population, even in areas where bTB is known to be a problem in cattle and also occurs in badgers. Let me back this statement up with some scientific evidence:

* Of 199 dead badgers found in the Woodchester Park study area in Gloucestershire (which falls within a known bTB area) from 1978 to 1993, only 14 (7%) of those animals had died from bTB while another 4 of the total were badgers found alive but killed by euthanasia, as they were in extremis with TB infection (giving a total of 9% of badger deaths attributable to bTB).  Even this was acknowledged to be an over-estimate of the proportion of badger deaths caused by bTB. As badgers in the study area known to be infected with the disease were fitted with radio-transmitters, those badgers were more likely to be found after death than those dying from all other causes apart from road traffic accidents. (RTAs claimed the lives of 132, or two thirds, of the dead badgers examined.) [4]

* Badgers at Woodchester Park from 1981 to 1994 which were found to be infected with bTB, but not actually infectious (in other words, they were not excreting bTB bacilli into the environment), had the same life expectancy as uninfected badgers. It was only those badgers which were found to be excreting bTB bacilli into the environment, and in particular those regarded as ‘super-excretors,’ which had a significantly lower life expectancy than uninfected badgers [5]. This indicates that badgers which are infected with bTB but not infectious are unlikely to suffer from the disease but in fact lead normal lives.

* An earlier study of badgers at Woodchester Park found that even those badgers with chronic bTB infection can cope “remarkably well” with the disease, to the extent that sows could produce and successfully rear cubs. [3]

* The Government’s Randomised Badger Culling Trial or RBCT (a.k.a. the Krebs trial) killed nearly 11,000 badgers in areas of England where bTB in cattle was a particular problems (the ‘TB hotspots’) from 1998 to 2005. You might expect that the proportion of badgers with TB in those areas would be high, yet only 16.6 % were actually carrying the disease in the pro-active culling areas and only 166 badgers (1.5 % of the total) were found with advanced lesions. [6]

* This compares with figures from Woodchester Park showing that the percentage of those badgers tested for bTB from 1982 to 1996 which were found to be super-excretors was, on average, only 1.6% each year. [7]

So, bTB does not pose a significant threat to the survival of badgers in Britain. And while it certainly causes suffering for the small proportion of badgers which become infectious and progress to the advanced stages of the disease, to suggest that the welfare of those individuals is best served by a mass slaughter of thousands of badgers, the vast majority of which would be healthy animals, is simply ludicrous.

Vaccinating badgers against bTB on the other hand would, over time, reduce even further the already small proportion of badgers which now suffer from the disease, without any collateral damage. And as the science sugests that increased levels of bTB infection in cattle leads to the same in badgers [8], tackling bovine TB in bovines, the primary host, would likely make an even bigger impact on the disease in both species.

[1] Driver, A (2010): Fitzpatrick denies bowing to welfare lobby on TB. Farmer’s Guardian (online), 18 Feb. Full article.

[2] Anon (2010): Badger TB “death toll” a myth, says Trust. Badger Trust (online), 25 Feb. Full document.

[3] Clifton-Hadley, R.S., Wilesmith, J.W. and Stuart, F.A. (1993): Mycobacterium bovis in the European badger (Meles meles): epidemiological findings in tuberculous badgers from a naturally infected population. Epidemiology and Infection, 111(1):9-19. Abstract.

[4] Rogers, L. M., Cheeseman, C. L., Mallinson, P. J. & Clifton-Hadley, R. (1997): The demography of a high-density badger (Meles meles) population in the west of England. Journal of Zoology, 242: 705-728. Abstract.

[5] Wilkinson, D. et al (2000): The effects of bovine tuberculosis (Mycobacterium bovis) on mortality in a badger (Meles meles) population in England. Journal of Zoology, 250 (3): 389-395. Abstract.

[6] Bourne et al (2007): Bovine TB: The scientific evidence. Final report of the Independent Scientific Group on Cattle TB. Full document.

[7] Delahay, R.J. et al (2000): The spatio-temporal distribution of Mycobacterium bovis (bovine tuberculosis) infection in a high-density badger population. Journal of Animal Ecology, 69 (3): 428-441. Abstract.

[8] Woodroffe, R. et al (2006): Culling and cattle controls influence tuberculosis risk for badgers. PNAS, 103 (40): 14713 – 14717. Full paper.

Discuss the issue of bovine TB on the Badger Message Board.

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