Mad cow prions may not be limited to just the nervous system, say researchers

• Mad cow disease has long been thought to occur in just the brains and nervous systems of infected animals.
• The research is based on experiments with mice, but if it is borne out in other species, it may suggest that no part of an infected animal is safe to eat.
• In humans, the disease manifests as a fatal brain infection.
• In the mouse experiments, reported in the journal Science, researchers in Switzerland worked with the proteins thought to be the infectious agent in mad cow disease.
• When these prions were given to mice that had been infected with chronic diseases of the liver, kidney and pancreas, they made their way to the infected organs.
• Dr. Adriano Aguzzi, a neuropathologist at the University Hospital in Zurich, who led the experiments, said this meant that cows and sheep infected with prions could harbor mad cow disease in any inflamed organ.
• Many countries, including the United States, require the removal of skull, brain, eyes, spinal cord and other nervous tissues from slaughtered animals, because prions are known to accumulate in those tissues.
• Even in countries with mad cow disease, which include Japan, Canada, Oman, Israel and 20 European countries, meat is considered safe if those tissues are removed, Aguzzi said.
• But the disease could spread more readily if infections are not obvious or inspections are done sloppily, he said.
• It is now collecting information on European farm animals, including sheep, which can carry their own prion disease, scrapie.
• While this has yet to be demonstrated in a cow, it has been seen in humans with sporadic Creutzfeldt-Jakob disease, which is related to mad cow but arises spontaneously rather than from eating infected beef or some other route.