By Elizabeth Weise, USA TODAY
Updated 6/18/2006 10:19 PM ET
The discovery of a new strain of mad cow disease that may strike spontaneously rather than through contaminated feed could mean that it will be impossible to completely stamp out the brain-destroying illness in cattle.
The only two cases of mad cow in U.S.-born cattle, found in Texas and Alabama, were a different form of the disease than the strain commonly found in Europe, French prion researcher Thierry Baron told scientists at a meeting in London in May.
Baron believes it is likely that the two U.S. cases — and at least five others found in France, Italy and Germany — occurred in a way that is strongly reminiscent of the most common human form of the disease, which is also not blamed on a contaminant. More research is necessary to know for certain, Baron said in an e-mail sent last week to USA TODAY.
If it can appear out of thin air to infect cattle as it does humans, "we may never be able to get rid of the disease," says Jean-Philippe Deslys, central coordinator of NeuroPrion, the network that coordinates European prion researchers.
Mad cow disease is known to scientists as bovine spongiform encephalopathy, or BSE. It is caused by infectious, misfolded proteins called prions. For most of the past decade, officials have focused their prevention efforts on banning the use of feed contaminated with infected cattle parts, believed to be the primary conduit of the disease.
Creutzfeldt-Jakob Disease (CJD) is the most common human form of prion disease. In almost 90% of U.S. cases, the prions spontaneously appear in the brain of CJD victims. About one in 1 million people, generally after age 60, are struck with the disease each year. Another 5% to 10% of CJD cases are tied to a genetic mutation.
There is no cure.
A similar but different disease is variant Creutzfeldt-Jakob, which people get from eating BSE-infected cattle. No one has acquired variant CJD in the USA; worldwide it has killed about 150 people.
Baron is quick to point out that it's not known if the spontaneously occurring form of mad cow can be transmitted by eating infected tissue.
Caroline Smith DeWaal, food safety director at the Center for Science in the Public Interest in Washington, D.C., says it's too early to say if this new strain is spontaneous. "But it does mean that ensuring that high-risk cattle material stays out of both human and animal cattle feed is essential," she says.
John Clifford, chief veterinarian of the U.S. Department of Agriculture, says feed bans across the globe have done an excellent job of stopping the transmission of mad cow. To him, what's most telling is that the number of cases is declining in cattle worldwide, as is the number of cases of variant CJD.
That's "a good indication that we're doing the right thing in control and eradication of this disease," he says.