Consumers worried about BSE and the safety of beef in the shops repeatedly ask the same, simple question: Why is the incidence of BSE still going up? If the Government's controls are so strict, why has more BSE been found here during 2000 than in any previous year?
The scientists researching this frightening disease offer little comfort for these same consumers. There are many aspects of the disease they just don't understand. There could be hidden ways for the disease to spread that we have yet to discover.
Dr Mark Rogers, of the Department of Zoology at University College Dublin, is one of Ireland's experts on BSE and related diseases. He admits scientists are puzzled by the rise in incidence. "We are not too sure why it is going up."
A key to the puzzle is finding the ways BSE can be spread. It all started when waste meat and bone was processed into a protein supplement for livestock. The product is thought to have harboured the disease which was picked up by animals that ate it.
An initial ban on the product was introduced in 1990 and then significantly tightened six years later, Dr Rogers says. "As long as we can stop the meat and bone meal, we should be able to stop the disease." The rush to understand the disease after it was discovered that BSE could transfer to humans, in a form called variant Creutzfeld Jakob disease, unearthed yet another means of transmission, he says.
There was some limited evidence of a 10 per cent chance that cows might pass it on to their calves if a BSE-infected cow was within six months of showing signs of the disease. This limited route, however, "would not sustain an epidemic", he says, and should represent only a tiny fraction of the current BSE caseload. "There is no other route of infection yet found," he says.
However, research announced in the UK only two months ago has raised new concerns. Researchers there found that mice given the disease could remain well but infective. In effect, they could pass on the disease to their fellows, killing them but remaining alive themselves.
This immediately brought into question the advisability of continuing to give the animal protein meal to other species. Legislation prevents its use in cattle, but not in poultry, pigs or fish. The ease with which BSE could infect other species varied greatly, Dr Rogers says. "You don't know which species might be carrying the disease," he adds, something shown clearly with the UK mice.
The assumptions suggest that being scrupulous about keeping protein meal away from cattle should bring down BSE incidence. "If we are right, we should expect to see a decline in the disease over the next two to three years," Dr Rogers says.
"The key figure to watch for is the ages of the animals, not the numbers," he adds. The increase in the number of cases here is very small compared to the size of the national herd and was not significant from a statistical point of view.
The latest controls have been in place for three years and if BSE cases begin to emerge in animals younger than three years, then all bets are off. It will mean something is wrong with the theory and there must be some other means of transmission, Dr Rogers says.
The implication would be that there was in fact some other mode of transmission that allowed the disease to survive and spread, raising further consumer doubts about beef safety.