BSE prions 'leak' into blood
Tests in hamsters suggest it may be possible to develop a blood test for mad cow and related diseases in both humans and animals before they develop symptoms, researchers report.
The study, published in the journal Science, also suggests that the damaged brain cells may 'leak' the infectious prions that cause the diseases, offering a chance to detect the disease in blood.
Such a test would allow animals to be checked before they enter the food supply.
It could also screen people, including blood or organ donors, for the rare but devastating Creutzfeldt-Jakob Disease or CJD, and its close cousin, vCJD, the researchers say.
Current tests require brain or other tissue samples.
Mad cow disease, formally known as bovine spongiform encephalopathy or BSE, is part of the family of prion diseases that also includes scrapie in sheep, chronic wasting disease in deer and elk, and CJD in people.
BSE emerged in Britain in the 1980s and swept through dairy herds. Some people who ate infected beef products developed a form of CJD called variant or vCJD and at least 191 cases have been identified, mostly in the UK.
People can have CJD before they know it and in a few suspected cases, blood and organ donors may have unwittingly infected others.
Professor Claudio Soto of the University of Texas Medical Branch at Galveston and colleagues infected hamsters with prions, the misfolded nerve proteins believed to cause the diseases, and then tested blood at various times.
They invented a technique known as protein misfolding cyclic amplification to accelerate the process by which prions convert normal proteins to misshapen infectious forms.
"With this method, for the first time we have detected prions in what we call the silent phase of infection, which in humans can last up to 40 years," Soto says.
Soto and his university have formed a company, called Amprion, to commercially develop the test.
Timing is crucial
The test may need to be used at precise times, the researchers say. It worked best in hamsters 40 days after infection. It did not detect prions 80 days after infection.
Then at 114 days, after the hamsters started showing symptoms, the blood test again revealed prions.
"It has been reported that large quantities of [infectious prions] appear in the brain only a few weeks before the onset of clinical signs," the researchers write.
A second study in Science shows that mice infected with prions develop heart disease similar to a type known as amyloid heart disease in people.
Dr Bruce Chesebro of the National Institutes of Health and colleagues say these diseases are marked by waxy protein deposits that stiffen the heart, limit its pumping ability and typically lead to fatal heart stoppage.
"Although several types of protein are known to form heart amyloid, this is the first time prion protein amyloid has been found in heart muscle and also found to cause heart malfunction," Chesebro says.