ISG report – is it robust science or just political?

The shock waves created by the release of the final report by the so-called Independent Scientific Group on TB (ISG) have left many bewildered as to how on earth the current TB epidemic is to be controlled.

The ISG is unequivocal that culling of badgers will cause the epidemic to worsen. They consider culling likely to spread infection by causing social disruption leading to a dispersal of infected badgers that would result in the problem spreading to neighbouring areas.

They refer to this as the “perturbation effect” and consider it almost an insuperable problem. While this must be music to the ears of Ministers, getting them off the hook yet again, is this really a valid reason – or is it more of the political science we have already heard from the ISG?

Their report is some 280-pages long, and most of the data they have used to arrive at their conclusions derives from the recent Randomised Badger Culling Trials. But as many of the farmers involved in this know, there were huge problems with these trials.

Defra wildlife staff were tasked with trying to catch the badgers in cage traps, yet trapping was continued for only an average of eight days per annum. Of the 15,666 traps set, 69 per cent were tampered with or stolen, and trapping was carried out when it was least likely to be effective during November to January in 16 of the 51 culls.

One of the Defra trapping managers was so concerned about the poor trapping efficiency and procedural interference by the ISG that he sent a written submission to that effect to the EFRA Select Committee, 2006.

All these problems, as well as landowner refusal to participate, added up to a disastrously low culling rate, confirmed by Defra of between 20 and 60 per cent.

This means from 80 per cent to 40 per cent of infected badgers were dispersed to spread their infection, making this more a study in dispersal of TB rather than a culling trial to control it.

However the ISG assert they removed between 32 to 77 per cent. But in all other trials in this country (Thornbury, Avon; Steeple Leaze, Dorset and Hartland, Devon) and in the Republic of Ireland (East Offaly and the Four Counties) culling success has been over 80 per cent.

In the trials using gassing in the mid 70’s, 100 per cent removal was achieved, resulting in complete cessation of TB cases over 10 years before other infected badgers moved in to start the problem again (Thornbury) and seven years in the other (Steeple Leaze). At the latter, the farming group switched to arable after that time.

Culling efficiency is everything when dealing with a wildlife reservoir host such as the badger that is organised into social groups. Due to the confined air space in the sett, mutual grooming and the gregarious nature of badgers, once there is a diseased badger in the sett, all inhabitants will become infected. Most infections remain in a dormant phase, with maybe only one or two developing progressive disease straight away. But the dormant cases may break down and develop disease as a result of stress caused by malnutrition, intercurrent diseases or social disruption. This is how poor culling approaches spread disease. So culling must always be aimed at complete removal of all the social group or sett occupants.

The culling method is crucial in eliminating infected groups and stopping spread to other badger groups and eventually cattle and the several other species that may pick up infection. To date this includes deer, alpacas, lamas, sheep, pigs, cats, ferrets and a dog.

Since badgers live in underground tunnel systems, the obvious approach is to try to dispatch them while they are still asleep underground, during the working day, by a toxic gas.

Carbon monoxide mixed with dioxide from petrol exhaust fumes would seem the obvious choice, but Defra has only recently started to test this approach and the trials and licensing of the method seem almost a year away.

Cyanide had been used previously, but while very effective, there were concerns about humaneness and, obviously, other connotations to its use. But it is only the gassing approach that has resulted in a certain and complete dispatch of all the sett inmates.

Waiting for badgers to emerge at dusk and chance catching them using traps or shooting them makes the likelihood of complete removal of social groups poor as well as logistically hugely more difficult. And the one unequivocal finding from the ISG is that if culling is not done completely disruption of badger groups and their dispersal will result.

In the MAFF annual report of 1995, the chief veterinary officer stated that 90 per cent of outbreaks were considered due to infected badgers and this was also affirmed by MAFF’s senior TB epidemiologist. Indeed, in the two gassing trial areas the complete cessation of TB in cattle following removal of the badgers indicated that they were the sole source of infection. Thus there, and throughout the areas where TB infection is endemic in badgers, cattle have been acting as sentinels of active disease in the badger. But the ISG say they have been unable to quantify the role of badgers in cattle outbreaks, although they do admit they can be a source of infection for cattle.

However, they consider that cattle-to-cattle transmission is greatly more important!

At the depressing ISG public meeting in London this week, we were assured that the only “robust and reliable” data that could be used to formulate policy for control of TB was that which had been produced by the ISG so-called culling trials. Despite all its problems they are adamant that their trials were indeed robust.

But it makes you wonder whether this is really robust science or political science?

• Dr John Gallagher is the former head of MAFF Veterinary Investigation Services for Devon and Cornwall and former Independent Advisor on TB to MAFF’s Chief Scientist Group.