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Gene mutation underlies some mad cow disease: study

WASHINGTON - A rare genetic mutation may underlie some cases of mad cow disease in cattle and its discovery may help shed light on where the epidemic started, U.S. researchers reported on Friday.

The mutation, in an Alabama cow that tested positive in 2006 for bovine spongiform encephalopathy, or BSE, is identical to one that causes a related brain-wasting disease in humans. This suggests BSE may sometimes arise spontaneously in cattle.

Jurgen Richt of Kansas State University said cattle producers must never let down their guard against BSE because cattle anywhere, at any time, can develop the disease.

The finding may support a 2005 theory that the BSE epidemic in cattle could be traced to feed contaminated with cattle remains from India, the researchers report in the Public Library of Science journal PLoS Pathogens.

BSE or mad cow disease swept through British dairy herds in the 1980s, forcing the destruction of millions of animals. No one ever found where it came from but most experts thought at the time it came from cattle feed that contained the remains of sheep infected with a similar disease called scrapie.

Cattle were never known to develop BSE before the epidemic, but some experts have argued they may have. This report lends credence to that idea.

BSE, scrapie and a human version called Creutzfeldt-Jakob disease, or CJD, are brain-destroying illnesses called transmissible spongiform encephalopathies. In some cases, animals or people that eat brain and nervous system material from victims of these diseases can develop them, too.

They are passed along by misfolded infectious protein fragments called prions.

'Another epidemic somewhere'

A very rare disease called variant CJD has been found in people who ate infected beef products. Fatal and incurable, it has affected just 167 people so far.

Most countries now ban the use of meat and other parts from mammals in food for cattle. They also ban the use of potentially infectious tissues such as brain and spinal cord in human food.

"There are tendencies around the world, now that the feed-borne epidemic has gone down, to relax these rules and regulations," Richt said in a telephone interview.

"So if we have these genetic cases popping up here and there and we don't have our mitigations in place, we will have another epidemic somewhere."

He suggested breeding the gene out of cattle. "We can clean the world cattle herd of that mutation," Richt said.

CJD is also known to pop up spontaneously in the human population. A genetic mutation causes the disease in one in a million people globally.

Richt and colleagues tested the brain of the Alabama cow and found a mutation identical to the prion gene mutation that causes some cases of CJD.

It is probably rare in cattle, found in fewer than one in 2,000, they said in the report, published at http://dx.plos.org/10.1371/journal.ppat.1000156.

But the animal passed along its mutation to its heifer, which suggests it is inherited.