Bovine TB vaccination

Written evidence submitted by Ian Kett

My name is Ian Kett. My wife and I farm 75 acres on the Quantock Hills in Somerset, grazing traditional cattle (English Longhorns) and sheep in an extensive system designed to favour conservation of wildlife and landscape. We have kept longhorn cattle for over 20 years. In January 2012 we suffered a severe bovine tuberculosis (bTB) breakdown along with all of our neighbouring farms. We lost 75% of our breeding cows, a junior bull and our stock bull.

I worked as a veterinary surgeon in large animal general practice for 38 years and my wife was a Defra Veterinary Officer in Devon from 1987 to 2007. We therefore approach the problem of bTB as scientists through our veterinary experience, as conservationists who have maintained badgers on our property and as farmers who have sustained heavy irreplaceable losses to pedigree breeding stock as a result of the disease reaching our premises.

The following is an unbiased appraisal of the facts pertaining to the control of bTB in the UK, as far as I am able to ascertain.

Overview

bTB has been the subject of control measures in this country since the 1950s. By 1984 the disease had been reduced to just 84 outbreaks nationwide, with around 400 animals culled. This had risen to over 30,000 reactor animals culled by 2005. From 1988 to 1997 the effect of badger protection legislation has allowed the population of badgers to rise by 77%. It is reasonable to assume that with this continued rate of increase, the population now exceeds 800,000 animals. This creates population pressures including fighting and forced migration due to feeding and territorial limitations, which in turn can affect the spread of badger transmitted disease.

During this period we have seen the number of badger setts on our land increase from nil in 1990 to 4 now.

Aside from the disease issues serious damage to infrastructure and wildlife has resulted. A national survey in 1997 estimated the cost of badger damage to be £25.7 million per annum, which included damage to roads, canals, parks, gardens, hedgerows and agricultural land. In addition feeding pressures have dramatically increased predation on ground nesting birds, bumble bees, hedgehogs, grass snakes, frogs and toads.

Hungry badgers have been forced into farm buildings in their search for food, thus increasing contact with domestic animals, in particular cattle through contamination of feed by badger urine. In 1995 the Chief Veterinary Officer concluded from an analysis of field outbreaks that 90% were attributable to badgers.

Vaccination

It will be apparent from the above that the badger problem is not primarily about bTB but rather it is one of overpopulation. Without addressing the latter there will be no solution to the former. Were it to be successful, vaccination would allow the badger population to rise further thus exacerbating the environmental damage. As an alpha predator the badger has no natural enemies in the UK.

BCG is the only vaccine at present available in the UK for the control of tuberculosis. BCG is only 70% effective in Man and of unknown efficacy in cattle and badgers. 2 doses have been shown to give protection to badgers as assessed by blood testing but not by assessment of clinical disease. There is no data to show a benefit from a single dose.

The presence of massive challenge to even the most effective vaccine will overcome vaccine derived immunity. Animals grazing grassland contaminated by diseased badger urine are exposed to millions of bacteria. This urine contamination is particular to the pathology of the disease in badgers, which suffer a fulminating form of the disease with urinary excretion a major feature. (Gallagher and Clifton-Hadley, 2000) In cattle, by contrast, bTB is chronic and walled off in tubercles or thick walled abscesses from which there is no bacterial excretion. These are most often in the lymph nodes. When in the chest lymph nodes or in the lungs these tubercles may discharge into the respiratory passages and create a low risk of infection to other cattle in a group by inhalation. There is thus some, but a relatively insignificant, risk of cattle to cattle transmission. This is borne out by the majority of outbreaks in housed cattle affecting small numbers of animals. By contrast, where feedstuff contamination is heavy, large numbers of cattle may be affected at the same time. When susceptible animals are removed from the source of infection, no further cases occur. This has been our experience in our 2012 outbreak where infected latrine sites on autumn grazing were involved. In addition a diseased badger was identified on our neighbour’s farm where there was a concurrent bTB outbreak. Unfortunately the badger carcase was not submitted for laboratory testing.

In order to achieve control of any disease in a population by vaccination, at least 70% must be vaccinated. Vaccination of badgers will cause perturbation as a result of trapping and injection. Serious welfare issues may result from repeated trapping and handling of badgers. Repeat doses of BCG can cause acute reactions and even death in man and possibly therefore in animals. Vaccination in cattle is not realistic as there is no benefit from the use of BCG. At the moment there is no test in cattle to differentiate reliably between natural and vaccination antibodies, raising issues of difficulties for future testing and international trade. The test that would be used is known as the DIVA test. The cost of using a DIVA test may be prohibitive to an already struggling industry (estimated at £26 per test) and may need to be repeated annually following routine tuberculin testing of cattle.

Eradication of any disease by vaccination depends on a highly immunogenic vaccine such as smallpox vaccine, from which a single dose confers lifelong immunity. There are no candidates for such a vaccine against bTB at present. BCG is unpredictable in the level of immunity it confers both in man and experimental animals. Experimental trials with BCG have been shown not to prevent infection or shedding of Mycobacterium by infected animals. It does seem to mitigate the effect of the disease, thus increasing the survival time of potential carriers and secretors. (Chambers et al. 2011).

Much of the pressure to vaccinate badgers and cattle is driven by political expedience. Eric Morley in the last Labour government was said to have told the Independent Scientific Group at the outset that a badger cull was politically unacceptable. It beggars belief that a government minister will put the loss of electoral support before the national interest.

There has been a sustained campaign of misinformation and cherry picking of scientific data by the Badger Groups and the RSPCA in support of their own ends. The RSPCA in particular was censured by the Advertising Standards Agency in 2006 and the Charity Commission in 2007 for publishing misleading information about the transmission of bTB.

The Way Forward

The gold standard solution would be the use of a single dose oral vaccine in badgers combined with badger population reduction to 1980 levels. The disease in bovines would be eradicated by continuing testing on an annual basis using the comparative intradermal test.

Since such a vaccine is not even on the horizon at the moment, the culling option for badgers is the only efficient management tool available. From the standpoint of public acceptability identification of infected setts and then subsequent eradication may offer a way forward (PCR testing). However this does not address the overall problem of a rising badger population.

Opposition to culling has been mounted mainly by referring to the Randomised Badger Cull Trial (RBCT) headed by Professor Krebs. This work has largely been discredited by independent observers owing to the lack of any peer review, and the conclusion that was drawn took no account of the poor cull rates achieved and the effect of significant disruption by animal rights groups. Almost 2000 incidents of trap destruction and release of trapped animals occurred during the trial period but no account was taken of this in estimating the reasons for badger perturbation and increase in disease outside the cull areas.

A substantial body of information exists in the literature confirming positive effects of culling badgers on the rates of bTB in cattle prior to the Krebs Trial. Professor Krebs dismissed these results as having no controls yet failed totally to take account of the incidence of disease in the areas surrounding the trial sites where disease levels in cattle remained the same as before the trials started. This effectively provided adequate control data.

The table below summarises the results of UK and Irish culling trials from 1975 to 2005:

Area (sq. km.) Culling Herd outbreaks

Thornbury 104 100% clear 10 years

Steeple Leaze 12 100% clear 7 years

Hartland Point 64 >80% 80-90% reduction 10 yrs.

East Offaly >38 >80% 88% reduction 7 yrs.

Four Counties 100x4 >80% 60-80% reduction

RBCT (Krebs) 100x10 30-70% 19-23% inside area

22-29% outside area

The admitted difficulties associated with an effective cull policy as opposed to  vaccination might be addressed as follows:

1. Remove the excessive protection of the Badger Act, thus rendering animal rights protesters unable to target individuals.

2. Enforce punitive measures against those convicted of badger baiting, including large fines, imprisonment and euthanasia of dogs used for baiting.

3. Allow humane destruction of badgers by landowners subject to a closed spring breeding season.

4. Limit cull methods to carbon monoxide or carbon dioxide administered in daytime when badgers will be asleep underground. If not killed the animals will emerge undamaged as the gas disperses harmlessly.

5. Shooting of individual badgers at dusk with silenced rifles remains an efficient tool in competent hands.

6. Monitor sett health using PCR testing – a technique that at present needs refining.

References

Gallagher and Clifton- Hadley, Res. Vet. Sci.( 2000),vol. 69, pp.203-217

Charles, Rodgers,Delahay et al. (2011) Proceedings of Royal Soc. Of Biological Science, vol.278, pp. 1913-1920.

January 2013

Prepared 1st February 2013