June 15, 2007

publication of report on badgers and bovine TB

Scientists commented on the publication of the report of the Independent Scientific Group (ISG) on cattle TB, which highlighted the high costs and low benefits of adopting a badger culling programme.

Dr Bernardo Villarreal and Dr Jayne Hope, Institute for Animal Health, said:

“Vaccination of cattle, in combination with better diagnostic tests, is likely to be the most effective strategy for the control of bovine tuberculosis (bTB) in the longer term. The only vaccine currently available for human TB is the live attenuated Mycobacterium bovis-bacillus Calmette-Guerin (BCG). It is likely that any vaccine or vaccination strategy for cattle will utilise BCG. However, the protection against TB that is conferred by BCG in people is variable. We do not know the reason for this. A greater understanding of why BCG confers protection in some cases but not in others will help us to develop better vaccines.

“At the Institute for Animal Health and in collaboration with the Veterinary Laboratories Agency we are testing vaccines against bTB in cattle. Our aim is to understand how the immune system of the cow eradicates M. bovis. Our hope is that this will lead to better vaccines and diagnostic tests for bovine TB.”

Andrew Biggs, Senior Vice President and TB spokesperson of the British Cattle Veterinary Association (BCVA), said:

“If we don’t do anything different, we shouldn’t be surprised if nothing different happens i.e. if we continue to test and cull cattle without addressing the disease in wildlife, the costs will continue and the disease will not diminish. This is evidenced by 10-15 years of experience.

“Potentially infected cattle are removed from the national herd by a TB test and slaughter of positive animals whilst no controls of any kind are applied to badger populations to remove or reduce infected badger numbers.

“There are plenty of examples of closed herds where TB free herds acquire infection with no cattle movements onto the farm and so the source is likely to be wildlife.

“We need to distinguish cattle translocation where an infected cow is moved from one herd to another or even one county to another taking TB with it, from the spread of disease between cattle by nose to nose contact within a herd or over farm boundaries. Quotes within the national press that cattle spread is the most significant factor miss the point that this is moving infection rather than spreading infection – a route that has in part been addressed by pre-movement TB testing at farmers’ expense.

“Cattle vaccination is fraught with difficulties because it is hard in TB tests to distinguish between vaccinated and infected animals. This has implications for whether the UK or even a herd could be declared TB free. Also, the vaccine must be 100% effective because one infected cow puts the whole herd under restriction and the test positive (reactor) cattle will be slaughtered – tending to negate any benefits of vaccination.

“Badger vaccination is practically difficult to deliver as injection of cubs before they exit the set to come above ground is near impossible and the delivery of oral bate (the favourite being peanuts) carries the risk of inadvertently vaccinating cattle, which would make them positive for the TB test. However, vaccination of badgers need not necessarily be effective for every badger, as reducing infection prevalence will reduce the spread of TB back to cattle.

“Both cattle and badger vaccines are 5-10 years away from use and in the case of badger vaccination, it will have no effect on the badgers currently infected in the population at large. If a vaccine were available and delivered to all badgers in the UK today, there would still be a time lag of 5-8 years (the natural lifespan of badgers) before a significant reduction in infected badgers would reduce the risk of spread to cattle. We cannot wait 10-15 years while vaccines are developed and delivered, so a combination of badger population control (culling) with subsequent vaccination as an exit strategy would seem a logical way forward.”