DEFRA and bovine TB - Dr Paul Gillett, M.B, Ch.B, MRCP, FRCPath
As a hospital medical consultant with 35 years experience specialising in microbial diseases and infection control, I would like to support the remarks made by Dr Ueli Zellweger.The decline of tuberculosis in humans in this country owes more to improvements in living conditions, better nutrition, less overcrowding and the pasteurisation of milk than it does to the introduction of BCG.
Studies on BCG vaccination in man show an efficacy of between 0% and 70% and appear to depend on country, nutrition and the prevalence of other mycobacterial infections in the population immunised. Thus a policy to control bovine tuberculosis based almost entirely on the use of currently available vaccines is unlikely to be successful even if one could achieve 100% uptake. Trials on new vaccines will take several years to complete given the chronic nature of the disease in both man and animals, and the outcome far from certain. In the short, and probably medium term this means the DEFRA policy is essentially do nothing.
It has to be understood that the current policy of testing and slaughtering infected cattle is aimed at preventing the acquisition of bovine TB by humans not cattle. As Dr Zellweger indicates in his letter, to control bTB in cattle one should be looking to prevent the transmission between and to animals in the herd. This would involve detecting and eliminating sources that pose a threat to cattle and unfortunately the badger is the most important wildlife reservoir that has close contact. I find it inconceivable that two species of animal that are susceptible to the disease and have proven close contact are not transmitting the disease to each other. Introducing proper control measures is therefore to the benefit of cattle, badger, farmer and the exchequer.
Why then are such measures not instituted?
Some would advocate the mass culling of badgers and one must suspect that it is fear of the political implications of public reaction to such a policy which bolsters DEFRA’s inactivity.
There is an intermediate and more appropriate strategy. I am reliably informed by countrymen that it is possible to detect diseased badger sets by inspection of the runs and other signs. Thus it is possible to avoid mass culling - which may actually be counter-productive - in favour of selective elimination of diseased animals. A measure which is to the benefit of the badger population as a whole and the cattle. A group of concerned West Country farmers and vets have recently produced a DVD* outlining the present problems and the potential for training others in the recognition of diseased sets. It is to be hoped that a coherent policy may be formulated about such an approach.
Should an effective vaccine and delivery system become available in due course, then it would be (as in humans) an adjunct to rather than a replacement for effective infection control measures.
* - Bovine TB – A Way Forward, a film by Chris Chapman, will be released at the end of January. For details go to the homepage www.chrischapmanphotography.co.uk and click on FILM
Email received January 8th 2010 from Dr Paul Gillett, M.B, Ch.B, MRCP, FRCPath in response to comments by Dr Colin Fink
- " I agree with the general thrust of his comments that no single measure is likely to be a panacea. I also agree with Colin what is required is a coherent and co-ordinated set of measures to reduce the transmission of bovine TB in badgers and prevent as far as possible the infection reaching cattle or alpacas.
Such a policy would need to include identification of infected setts, something I am assured is possible by informed assessment. The assessment would need to be co-ordinated with cattle testing so that infection in cattle and badgers are treated at the same time. If this is not done at the same time there is a real danger of shuttling infection between the two. Assessment of badgers could be done either only when positive cattle reactors are found- the cheap option or when ever the cattle are tested. If signs of diseased setts are found I believe with the currently available technology it is not possible to distinguish reliably between infected and non-infected animals. Dormant infection which reactivates at times of impaired immune function, stress or malnutrition is a well recognised feature of mycobacterial disease. Once an infected sett is identified I really see no viable option to eliminating the whole sett population and destroying the sett because not only may the sett contain viable bacteria but they may also contain dead badgers that have died from TB. Whatever the detail it would need to be clearly stated and controlled.
On a more general point it is important that the badger population in an area does not outgrow the available food supply. Malnourished animals are not only more susceptible to disease but are also more likely to forage for food in farm buildings and have closer contact with cattle. I know of at least one farmer in a bTB 'hotspot' who feeds the badgers on his land and by good fortune or good animal welfare his herd has remained free of infection despite disease on neighbouring farms.
The suggested use of contraception for badgers is an interesting one worth investigating and could be a humane way of keeping populations within their food supply.
I have some reservations about the use of antibiotic therapy. Multi drug resistant tuberculosis is causing increasing concerns in humans and I fear that the use of antibiotics in the wildlife populations could produce just the conditions of suboptimal, intermittent dosage that would promote the development of more antibiotic resistant strains.
Email received from Dr Paul Gillett Jan 16 2010
- Dear Mary,
I, reluctantly, am re-entering the bovine TB debate. Reluctantly because as a 'medic' rather than a vet or farmer I could be seen as trespassing in someone else's garden.
However I find the recent correspondence on vaccines rather depressing. Vaccination is talked about with the implication that an effective vaccine is on the verge of being released and will solve all the problems with bovine TB. Nothing could be further from the truth.
Vaccine studies in New Zealand - who are much further on than we are - have been conducted in trapped possums, the main wildlife reservoir in that country. The results for challenge studies show an efficacy for an oral formulation of BCG of about 60% and slightly more for an injectable when compared to similarly challenged unvaccinated controls. In the wild, delivery of the vaccine by either trapping or food baiting is likely to give vaccine coverage a long way short of the 100% in these reported studies.
It remains to be proven whether a less than optimal vaccine with unknown levels of vaccine exposure is sufficient to control the disease in wild animals.
Such studies will take many years to perform and will need very careful control of other factors that could alter the results.
With regard to vaccination of cattle, administration of a vaccine is less of a problem; however we will require a routine i.e. inexpensive and accurate, test system that reliably differentiates vaccinated cattle from diseased. Even if such a test became available it would require legislative approval before it could be used in trials of candidate vaccines. Given that the process will take a minimum of five years and probably at least ten and that trials on efficacy will then have to be performed, it can be seen that vaccination of cattle is a long way off. At the end of that laborious process we may still be left with a vaccine that is less than 70% effective.
Research into possible use of vaccines should of course continue but should be seen as exactly that - research. At present a control policy based on vaccination with all its attendant uncertainties and prolonged delays is a luxury we can't afford to consider at a time of increasing numbers of affected cattle and badgers.
Talk of vaccination is an unfortunate or contrived distraction from the main issue of producing a coherent, co-ordinated set of measures to control the disease in animals, this will need to include, however unpalatable, selective culling of badgers as it currently does of cattle. Anything less than that will be a disservice to farmers, cattle, badgers and the tax payer.
Kind regards,
Paul