Subject: Prion disease found lurking in deer muscle
Date: January 26, 2006 at 11:44 am PST
Prion disease found lurking in deer muscle
19:00 26 January 2006
NewScientist.com news service
The infectious prions that cause Chronic Wasting Disease, an infection similar to BSE that afflicts North American deer and elk have been found in the parts of the animals that people eat. No one knows if CWD can jump to humans, but if it does hunters in affected areas might be at risk.
CWD was first diagnosed as a spongiform encephalopathy in captive deer and elk in Colorado in the 1970s, and in wild deer and elk in the region in the 1980s. But in the 1990s it spread widely within the elk farming industry, jumped to wild deer, and now affects two provinces of Canada and 13 US states.
Like the related sheep disease scrapie – though unlike BSE – CWD spreads from animal to animal, says Glenn Telling of the University of Kentucky at Lexington, US. Deer housed with infected animals, or fed infected brain experimentally, contract the disease.
Because of this there are fears that the CWD prion might be distributed widely in the deer’s tissues – as scrapie is in sheep. Efforts to find the infectious prion in the muscle of infected animals, by seeing whether antibodies to the prion could find any and bind on, have previously failed.
But Telling’s lab has now shown that diseased prions can reside in muscle of deer infected with CWD, by using transgenic mice.
The team replaced the gene for the normal mouse version of the prion protein with the normal gene from deer, so the mice made the normal, healthy deer protein. They then injected the mouse brains with tissue from infected deer. Twelve to 18 months later, the mice developed encephalopathy.
Tissues from both the infected deers' brains and thigh muscle caused disease. Muscle took slightly longer to cause disease than brain tissue, showing it had slightly less prion.
“We don’t know that it is transmitted in the wild by animals eating muscle from infected animals,” cautions Telling. “We now have to see where else the prion might be,” including saliva and even excrement, using more transgenic mice.
“Because we tested deer that were already ill,” he told New Scientist, “we don’t know what the distribution of prion is in animals that are still incubating the disease.” Hunters have been warned by wildlife agencies not to kill and eat obviously ill animals, but an animal not yet showing signs of the disease might still carry the abnormal prion, albeit less of it.
It is also unknown whether people can catch encephalopathy by eating CWD-infected meat, as they can from eating BSE-tainted meat. Anecdotal reports that hunters develop the human prion disease CJD in unusual numbers have never been confirmed. State officials have issued warnings to hunters not to eat brain or spinal cord – the tissues most affected.
“If I were a hunter I would be cautious about eating deer in areas affected,” says Telling. But he notes that not much testing of wildlife has been done, and it is not clear how prevalent the infection is.
Journal reference: Science (DOI: 10.1126/science.1122864)
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