BSE in sheep and goats?
Despite the huge amount of publicity it has received, bovine spongiform encephalopathy (BSE) or «mad cow disease» and the full extent of its effects are still largely an unknown quantity. It is not yet known whether some form of the disease may affect sheep and goats, so the European Union has decided on precautionary steps. Kathimerini spoke to some experts conducting research into BSE. ‘The matter is not yet resolved’ Theodoros Sklaviadis, assistant professor of pharmacology at the Aristotle University of Thessaloniki, is researching BSE. He says the disease is still a mystery: «Contagious spongiform encephalopathies affect the central nervous system. They affect man and animals, chiefly in the form of Creutzfeldt-Jakob disease, scrapie and BSE. We don’t know exactly how they are transmitted. Research shows that a protein common to all humans and animals is part of the pathogenic factor, but it has not been proved whether it is exclusively responsible for the infection. The matter hasn’t been resolved yet.» Given the complexity of the problem, the emphasis in recent years has shifted to timely diagnosis and preventing the disease from spreading from one species to another, says Sklaviadis. «Consumption of animal products has dropped drastically in the EU since the Creutzfeldt-Jakob cases were diagnosed in France and Britain,» he adds. «Already there have been 111 cases and nobody can predict how many more will arise in the next 10 years. «The EU has adopted stricter measures to encourage consumer confidence. For example, it lowered the age of cattle destined for testing after the slaughters of July 1, 2001 from 30 to 24 months. And there are also systematic efforts to implement new sensitive molecular techniques for detecting the disease at a preclinical stage and keeping apparently healthy animals that are infected by it out of the food chain. «This will bring the age limit for testing down even lower.» Although the same methods are used in Greece as in the rest of Europe, the number of samples taken is far lower and must be increased, Sklaviadis believes. He would like to see the samples, which are currently the property of the veterinary authorities, become available to other public agencies and for research purposes. The EU has taken political and scientific measures to address the likelihood that BSE can spread from one species to another. «Since there are some 22 million sheep and goats in Greece,» says Sklaviadis, «the agencies involved must be ready to conduct the tests and request funding to cover at least part of the cost.» ‘The disease is always fatal’ Dr Ruth Gabizon works at the Hadassah Medical School in Israel and collaborated closely with Dr Stanley Prisner, who won a Nobel Prize for demonstrating the connection between BSE and prions. She spoke to Kathimerini about recent developments concerning BSE. Gabizon believes the EU is doing its best to prevent the spread of BSE. «There is no irrefutable proof,» she notes, «that cows developed a new form of BSE because their food contained sheep products contaminated with scrapie, though this is the dominant theory at the moment.» Asked about the likelihood that sheep have been infected with a new form of the disease that they might transmit to humans, Gabizon explains: «Scientists in England are conducting experiments to see if BSE can be transmitted to sheep that so far only have scrapie. There are no results as yet. But it is a very important question, because so far no human has been infected by sheep with scrapie, whereas BSE can be transmitted to humans.» Gabizon has discovered that prions, the proteins that carry BSE, can be detected in the urine of humans and animals infected with spongiform encephalopathies. «But so far,» she says, «we cannot measure the level of infection in the urine, which would allow us to detect the disease before the animal was slaughtered. We are continuing the experiments but it will be at least a year before we have any results.» It is not yet known for certain whether BSE can be passed on from mother to offspring among humans, mice, cattle or sheep. As Gabizon explains, the only method of transmission about which there is any certainty so far is that of feeding animals with products from diseased animals. «There may be other methods, but then the chances of infection decrease and the incubation period and appearance of the disease are very long. But it is important to point out that from what we know, regardless of the ‘dose’ and the incubation period, the disease is always fatal.» The evidence suggests that some individuals have a genetic predisposition to contract the disease, says Gabizon. «It seems that the infection factor is affected by other genes that have shown a particular permutation in all the people who have so far contracted the disease. But this permutation is common to many people, so it’s hard to be certain that a genetic predisposition exists. It may eventually turn out that genetic predisposition has more to do with the incubation period and not with the emergence of the disease.» Even after many years of research, the nature of the disease remains unknown, says Gabizon. «We know that the protein prion plays an important part, but the way in which it causes infection is still unclear. We hope to get a fuller picture.» One case among 12,000 animals The statistics show that one animal in around 12,000 tested has been infected by spongiform encephalopathy. The first case in Greece was discovered after 6,000 inspections. The total number of cattle in Greece is around 650,000, of which 315,000 each year are destined for slaughter. Of these animals, 50-60 percent are aged 16-24 months, while the remaining 126,000 are older than 24 months. By September 2001, tests had been conducted on 11,518 animals aged over 30 months, according to the Agriculture Ministry.
