2004-1-20
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.