This is the VOA Special English Health Report.
In December, the United States reported its first case of mad cow disease. Agriculture officials have been working to make sure other cows that came from Canada with that animal are not used as food. This is because of the possibility that people who eat infected beef can get a human form of the disease. Officials say more than one-hundred-forty people in Britain have died since an outbreak of mad cow disease in the nineteen-eighties. Ten deaths have been reported in other countries.
The scientific name of the cattle disease is bovine spongiform encephalopathy. A similar disease in sheep is known as scrapie. Deer and elk suffer chronic wasting disease. And minks get a disease called transmissable mink encephalopathy.
In humans, there is a disease in babies called Alpers syndrome. Other similar diseases in people include fatal familial insomnia, kuru and Creutzfeld-Jacob disease. The human version of mad cow disease is a form, or variant, of Creutzfeld-Jacob.
All these diseases create holes in the brain. All kill. And experts say all are caused by infectious proteins. American scientist Stanley Prusiner discovered this kind of protein in the early nineteen-eighties. He named it a "prion" [PREE-on]. He won the Nobel Prize for Medicine. Prions contain no genetic material. So they cannot copy themselves the way bacteria, viruses and other infectious agents do.
Prions are found naturally in brain cells of people and animals. Research published last month in Cell magazine suggested that prions could help the brain store memories. But experts are not sure of their purpose.
Prions appear to do no harm until one changes shape. Normally a prion is round like a ball. The protein becomes dangerous when it unfolds into a straight line. When it touches another prion, the second one unfolds and touches another. That one also unfolds, and so on.
This process can start naturally. Or it can begin when an unfolded prion enters the brain of a person or animal that has eaten infected tissue. This is why farmers are now banned from feeding cows the remains of other cows and sheep.
Researchers are trying to discover more about prions. A big question is why only some people who ate infected beef have gotten sick.
This VOA Special English Health Report was written by Nancy Steinbach.