Dear Editor, I am a retired research scientist and have followed the debate on badgers and bovine TB closely and with something approaching despair.

In her letter last week Dr Sarah Wheeler, a vet, is the latest professional to defend the proposed cull of badgers. In her letter she rightly states that in the summary of his report Sir David King indicates that badgers are a clear source of infection for cattle and that removal of them in areas of high incidence appears the best option "available at the moment". She does not mention that in the main text of his report King identifies many frailties in the available data and stresses that many uncertainties remain. He goes on at considerable length to point out that, on the evidence available, the balance of probabilities is very slender - not even reaching the lowest, 5%, level of statistical significance. It is quite inconceivable that a national programme for treatment of any other disease would be instigated with such doubts remaining. Surely we do not want our vets and scientists to wantonly abandon established scientific principles simply because badgers can't sue.

Dr Wheeler also raises the spectre of bovine TB infection in humans. It is widely presumed that pasteurisation has condemned this issue to history. Not so - it is very alarming, but maybe more so for livestock than humans. The disease is only ever discussed and investigated as animal to human infection, the possibility (probabiliity?) of human to cattle transmission is never mentioned, nor, as far as I am aware, has it ever been investigated. In the last 15 years there have been a number of published studies that review the incidence and epidemiology of bovine TB infection in humans. Between 1990 and 2003 there were between 17 and 50 cases in the UK (enequivocal diagnosis was not always fully established). All the studies recognise that humans may act as a reservoir for the disease. In some humans the development of TB was from latent, pre-pasteurisation infection. What this means is that humans can be carriers without showing clinically important symptoms for decades. Can farmers, stockmen, vets, marketmen and others in close proximity to cattle guarentee that they do not carry M. bovis - does anybody know? Could this be the explanation for the bovine TB in those areas where the bacillus type differs in the cattle and badger population, and where cattle movement does not provide a certain explanation?

Infection with bovine TB is mostly from an airborne saliva/mucus aerosol which can remain live and infectious for several hours (mean half-life 1.5h). Do stock-workers take precautions not to carry such infectious saliva aerosols on their clothes or in the air from their lungs when visiting neighbours, markets, county shows? The survival times for M. bovis would permit transference over fairly large distances, without moving any cattle. Unlikely I would accept, but uninvestigated and possible certainly. And what about the long-term human carriers, known to be there but similarly unidentified? The King report makes it clear that similar unknowns exist in the presumed badger to cattle infection route.

Surely we should be fair and seek answers to these unknowns before initiating such a drastic measure as mass extermination of a species. After the badgers, is it to be farm cats, ramblers, men from the ministry, vets, ...?

Yours sincerely, Mike Snow, Blaencoed, Eglwyswrw,