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- Now, six years after young people in Britain started
dying from a human strain of mad cow disease, scientists are still struggling
to understand how the disease spreads to humans, how many more will die
from it and if a similar epidemic could start in the United States spread
by infected deer and elk.
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- While there are no firm answers, clues are being discovered
on an almost weekly basis as scientists explore the nature of a mysterious
infectious agent called the prion.
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- Unlike disease-causing viruses or bacteria, prions are
normal proteins found throughout the body tissues of humans and other animals.
But for reasons that are not at all understood, normal prions sometimes
transform themselves into tiny particles that cannot be killed with boiling
water, chemical disinfectants or strong radiation.
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- These prions, almost impossible to destroy, accumulate
in the brains of infected animals and people, destroying cells and leaving
spongy holes in the tissue.
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- The most common human form of this malady, called sporadic
Creutzfeldt-Jakob disease or C.J.D., seems to arise spontaneously in the
brains of about one per one million people. An estimated 300 Americans,
mostly over age 50, die from it each year.
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- But a new variant of C.J.D. now is killing young Britons
who acquired the disease from eating cattle infected with abnormal prions
of their own.
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- The cattle malady, called bovine spongiform encephalopathy
or mad cow disease, has infected hundreds of thousands of animals since
the mid-1980's.
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- Two weeks ago many of the world's leading prion researchers
went to Miami to meet with the families of American victims of sporadic
C.J.D. and to tell them everything that was known about prion diseases.
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- "It was a unique medical conference," said
Cecile Sardo, secretary of the Creutzfeldt-Jakob Disease Foundation in
Miami, which organized the meeting on May 7 and 8. "When scientists
get together they talk technically," she said. "They rarely talk
in person to families."
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- Of the 125 people attending, half were family members
and half were medical professionals.
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- Dr. Stephen DeArmond, a pathologist at the University
of California School of Medicine at San Francisco, explained that the normal
prion protein was folded in a loopy pattern resembling corkscrews. But
when it misfolds and acquires ribbon-like sheets, the prion becomes deadly.
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- When a misfolded prion comes into contact with a healthy
prion, he said, it can sometimes force the normal prion to change shape.
The process continues, like a nuclear chain reaction, until the brain is
destroyed.
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- It was recently proved beyond doubt that new variant
C.J.D. was a human form of mad cow disease, said Dr. Robert Will, a neurologist
and director of Britain's National C.J.D. Surveillance Unit in Edinburgh.
This new disease could eventually kill tens of thousands of people in Britain
or, given the many uncertainties about prion diseases and long incubation
periods, it may eventually die out, he said.
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- Thus far 56 people in Britain, 2 in France and 1 from
Ireland have died of new variant C.J.D.
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- British health officials recently found a method that
might assess the scope of the epidemic, Dr. Will said. Unlike the mis folded
prions in sporadic C.J.D., which are found exclusively in brain tissue,
new variant prions are found in the brain, tonsils, appendix, spleen and
lymph nodes.
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- One of the biggest mysteries is why the new variant form
of the disease attacks young people, Dr. Will said. The British victims
were 13 to 43 years old, whereas sporadic C.J.D. affects much older people.
Dr. Will said that one possible explanation was the widespread use of "mechanically
extracted meat." After meat is removed from the carcass, he said,
it is compressed with a machine not unlike an automobile crusher used in
wrecking yards. Bone comes out one end and a meat-like goo at the other
end.
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- This "meat" was once widely used in baby food
and institutional school meals, Dr. Will said. It was fed to children all
over the country, but the link between eating the food and getting the
disease has not been proved.
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- No cases of new variant C.J.D. have been found in the
United States, said Dr. Lawrence Schonberger, an assistant director for
public health at the Centers for Disease Control and Prevention in Atlanta.
There have been a few instances of deaths of younger Americans from C.J.D.,
but tests of their brain tissue showed that they had sporadic forms of
the disease, he said. But according to Dr. Michael Hansen, a research associate
at Consumers Union in Yonkers, deer and elk in several western states are
experiencing a growing epidemic of a prion disease called chronic wasting
disease.
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- In Larimer County, Colo., 15 percent of deer are infected,
Dr. Hansen said. Some experts fear that many hunters and their families
have almost certainly been exposed to the misfolded proteins from eating
infected deer and elk meat, Dr. Hansen said. But it is not known if the
deer version of the disease has been transmitted to humans.
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- Such transmission is possible, said Dr. Byron Caughey,
a senior investigator at the Laboratory of Persistent Viral Diseases of
the Rocky Mountain Laboratories in Hamilton, Mont.
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- Results of experiments, to be published soon, show that
the misfolded deer prion can, in a test tube, convert normal human, sheep
and cattle prions into deadly prions. The rates are very low, he said,
but conversions can occur.
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- At the end of the meeting, family members stood at a
microphone and told researchers horror stories about how their loved ones
had been told, wrongly, that they had Alzheimer's disease or got no satisfactory
diagnoses at all. Many said that local pathologists, fearing prions, would
not carry out brain biopsies and that some morticians had refused to embalm
the bodies of C.J.D. victims.
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- Families are confused and angry, said Mel Steiger, an
engineer from Salt Lake City, whose wife died of sporadic C.J.D. two years
ago. They want to know if there is an environmental factor in the disease,
and, he said, they worry that officials in the United States are not doing
enough to monitor the situation.
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