Where badgers boldly go

One moonlit night about 20 years ago, two badgers were seen crossing a long (2.5-kilometre) causeway at low tide to an island off the coast of Connacht. A year or two later, the first cubs were seen playing near the island's lake. Today, after slow expansion, more than 20 badgers live on the island, all rather smaller than those on the mainland and all, except one, with distinctive white noses.

This self-contained little colony of badgers is of striking importance, first to zoology in general, but also, potentially, to the future welfare of the whole Irish tribe of Meles meles, now some 230,000 strong .

It is the first recorded example of badgers actually in the process of colonising an Irish island. This relates to a long scientific controversy about the way in which some mammals reached Ireland. Did they venture across long and gravelly post-glacial land bridges from Britain, or were they introduced later by people? The western white-noses show that badgers may be more adventurous than we thought and that Meles meles is indeed a "natural" member of the Irish fauna.

The colony's investigation by biologists has led to the discovery of similar groups of badgers on several other uninhabited islands around the coasts of the west and south. Some of these are largely sand dunes. "It's akin," says one researcher, "to finding badgers in the Sahara".

Such unsuspected colonies are vital to a new, multinational effort to find a vaccine to protect badgers against contracting bovine TB. This would provide an alternative to extermination strategies which have cost thousands of Irish and British badgers their lives.

It parallels a vaccine project in New Zealand, where millions of brush-tailed possums are among the wildlife similarly blamed for re-infecting cattle herds.

The project in Ireland is run and funded by the Department of Agriculture and involves a multidisciplinary team drawn from UCC, UCD, Duchas and department vets, as well as government scientists from the UK and France. It follows field trials in Co Cork in the early 1990s in which badger setts were baited with chocolate bars wrapped around capsules of a dead vaccine.

These trials showed that an oral vaccine can be delivered successfully to badgers. But the vaccine itself was a failure: after five years, there was just as much infection in the animals and local cattle. The animals were under constant stress, as farmers persecuted them and destroyed their setts, and this could also have affected the outcome of the trial .

In the windswept but otherwise peaceful settings of the new study, the badgers have been coaxed with peanuts into traps and inoculated with live BCG, the same anti-TB vaccine used in millions of doses in human disease-control programmes. At the main location, a team led by Dr Paddy Sleeman of UCC has trapped and vaccinated half an island population of about 30 badgers, leaving the rest as controls. Isolated from the mainland for a century or more, they are all healthy animals, free of TB, and are being retrapped periodically to measure their protective immune response to the vaccine.

The outcome is highly uncertain, and the enthusiasm of scientists for a badger vaccine has had to overcome a lot of scepticism. New strains of genetically-modified live vaccine may yet have to be developed, and tested for stability and safety, and this adds to the islands' importance for experiments in isolation. Why does there need to be a vaccine for wildlife: why not one for cattle? The overriding reason is that vaccinated cattle could test positive in skin tests, and so compromise the existing system used to monitor the herds. The recent review for the UK government by Prof John Krebs and an independent scientific team held that "in the long run, the best prospect for control of bovine TB is to develop a vaccine for cattle" - perhaps one with a distinctive molecular flag. Even after almost 30 years, the link between badgers and bovine TB remains scientifically unproven: the route of transmission is unknown. Krebs listed possible contact through "behavioural changes" in badgers dying of TB, and through cattle sniffing grass marked with badger faeces, urine or sputum. Cattle "smell by first exhaling strongly, thus creating an aerosol" which they then inhale.

After decades of research, it is amazing to be left with no more than hypotheses. The evidence for the re-infective role of the badger is all circumstantial but it is strong and substantial.

Some of it comes from the Irish pilot experiment in which almost 1,800 badgers were removed from 738 square kilometres of east Offaly. The incidence of TB in cattle was then compared with that of the surrounding area. The level of disease in cattle did, indeed, fall, but the experiment was "confounded" because movement of badgers between the areas could have confused the results.

Now, the trial is being repeated, comparing four widely-separated new clearance areas with other "reference" areas in the same county, but not directly adjacent. In Donegal, Monaghan, Kilkenny and Cork, more than 1,300 badgers have been snared and shot since 1997. About one in five of them was found to have TB, and the impact of their removal on levels of infection in cattle will be reviewed in 2002.

It is not only in Ireland that official strategies have been faulted for poor science. In the UK, where badgers have been culled in south-west England since the 1970s, TB in cattle has actually increased. A key outcome of the Krebs report is a properly randomised trial spread over at least 30 "hot-spot" locations. It will test the worth and cost of all the options. There are those who will not accept that badgers can give TB back to cattle and don't want them touched for any purpose, and those who think that large-scale slaughter is the only means of control. Between the two extremes there is probably a whole armoury of options, to which even a moderately effective badger vaccine could be vital.