A study published Tuesday in the Proceedings of the National Academy of Sciences makes clear that people in Britain who developed a new type of Creutzfeldt-Jakob disease could have gotten it from eating meat from cattle infected with bovine spongiform encephalopathy, the so-called mad cow disease.
Neither mad cow disease nor the new type of Creutzfeldt-Jakob have been confirmed in the United States.
Experts said the study also suggests the infectious protein, called prion, that causes the diseases can move more easily between species than once believed.
"These findings argue unequivocally that BSE and the new variant CJD are the same strain of prion," said Dr. Stephen DeArmond, a researcher at the University of California, San Francisco, and a senior author of the study.
An outbreak of BSE occurred in British cattle early this decade. Later, some people in Britain developed a new, more deadly type of the Creutzfeldt-Jakob disease. In 1996, experts suggested mad cow disease possibly could be linked to the brain-wasting human disease.
The European Union banned import of British beef for three years until last August. France still bars import of the meat. Officials in Britain banned sale of bone-in domestic beef in 1997 and lifted the sanction last Thursday.
More than 175,000 British cattle died of BSE during the 1990s. At least 48 people in Britain have died of the new form of CJD, along with two in France and one in Ireland.
Although a link between mad cow disease and the new type of CJD had been suggested, there were experts who questioned the connection and contended a true scientific link was lacking. The new San Francisco study virtually removes doubt, said Dr. Donald Price, a neurological disease researcher at Johns Hopkins University in Baltimore.
"This lends new credence to the idea that the new variant CJD is a direct result of consuming products from animals with BSE," Price said Monday. "It is something the European community should be concerned about."
Officials for the British health and agricultural departments in London declined comment Monday, saying they had not read the new study.
Since the new form of CJD is thought to have an incubation period of at least 10 years, experts say it is impossible to know now how many people have been infected.
Co-authors of the study include Dr. Stanley Prusinger, a UCSF professor who won a Nobel Prize in 1997 for his discovery that the protein prion caused BSE.
In the study, researchers created a strain of mice that had genes for the normal form of bovine prion protein. The mice were inoculated with prions taken from diseased cows.
After 250 days, the test mice all developed neurological disease.
In another group of thmice, the researchers injected priors taken from patients who had the new form of CJD. After 250 days, these mice also developed neurological disease.
Prions from the diseased mice were then injected into a third group of mice. They also developed the disease.
DeArmond said the mice with the disease had identical symptoms and incubation periods. Also, a microscopic examination of their brains showed the same type of lesions. In CJD, the brain is pocked with holes caused by the death of cells.
Mice injected with scrapie, a sheep form of prion disease, got neurological disease, but it was different from the infection linked to BSE, researchers said.
BSE is thought to have developed in British cattle whose feed contained protein from sheep that had been infected with scrapie. Britain now bans the use of animal parts in cattle feed. In the United States, the FDA issued a similar ban in 1997.
Prions, a name standing for "proteinaceous infectious particles," are usually normal proteins found in most mammals. But when the prion shape is changed -- either from infection or from contact with another malformed prion -- the particle can cause brain disease.
Because it attacks the brain, symptoms can include bizarre behavior in animals. For this reason, BSE is often called "mad cow disease."
By Paul Recer
©1999 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed