Biologists Say Hunters Should Beware of Brain
Disease
nytimes.com
"Likening the situation to the early
days of the mad cow epidemic in
Britain, some biologists say
American hunters should be warned
about a similar malady that has infected
wild deer and elk in parts of Colorado
and Wyoming.
The malady is called chronic wasting
disease. While no cases of human
disease have been directly traced to
deer or elk meat, there is a growing
body of evidence to suggest that it
could happen. And with the hunting
season in full swing, a number of
scientists are calling for more action to
warn hunters about the potential
problem.
Both mad cow disease and chronic
wasting disease are believed to be
caused by aberrant proteins, called
infectious prions, which affect the
brain, destroying tissue and leaving it
with sponge-like holes. When the cow
disease first appeared in Britain in the
mid-1980's, government agriculture and
health officials initially offered
assurances that it could not spread to
people.
By now, though, 77 Britons have died
of a related brain disorder that they are
believed to have contracted from
consuming affected meat. It is not
known how many others may
ultimately fall ill and die.
Eventually, the British government
destroyed almost four million cattle to
stem the spread of the disease. But last
week a three-year investigation into the causes of the epidemic severely criticized
the government's "culture of secrecy" in not being more honest with the public,
and for using "an approach whose object was sedation."
Wildlife officials in Colorado and Wyoming, where the chronic wasting disease is
firmly entrenched along their shared border and is estimated to affect 1 percent of
elk and from 6 percent to 15 percent of deer, insist that not enough is known about
the problem to cancel hunting permits.
Dr. Mike Williams, a veterinarian at the Colorado Department of Wildlife in Fort
Collins said, "We don't think the problem is a big deal." Areas where the disease is
endemic are not closed to hunting, nor is there a need to close them, he said. "If
people choose to hunt there, it is their choice," he said.
Instead, hunters are advised by state wildlife officials to avoid obviously sick
animals and to use rubber gloves in cutting up all carcasses, particularly brain and
nervous tissues where the infectious prions apparently concentrate. But people
familiar with hunting practices in those areas say hunters are not taking even these
precautions.
"Around here, people are not knowledgeable about the disease or just don't care,"
Arnold Hale, a retired hunting outfitter from Livermore, Colo., said in a telephone
interview. "When you talk to hunters, most don't trust the government. I don't
know anyone taking precautions."
Kurt Zunker, 28, a probation officer from Cheyenne, Wyo., who is an avid hunter,
said: "I'm aware of the situation but not really abreast to the complete ramifications
of it. It won't stop me from hunting."
Mad cow disease and chronic wasting disease are among a bizarre class of
prion-caused disorders known as transmissible spongiform encephalopathies or
T.S.E.'s. The aberrant protein molecules are folded abnormally, which seems to
endow them with their ability to cause disease. Sometimes they seem to misfold all
on their own. In other cases, the misfolded proteins are transmitted via food, blood
transfusions or surgical instruments.
Transmission is difficult to track, however, because people or animals typically
develop the disease a long time after they have been exposed to the misfolded
prions. Until a few years ago, for example, it was widely believed that each animal,
including humans, had its own unique form of T.S.E. and that the diseases rarely
passed between species.
But in 1996, when young Britons began dying from a particularly rapid human form
of the disease, Creutzfeldt-Jakob disease, or C.J.D., the species barrier began to
crumble. Until then C.J.D. was diagnosed exclusively in much older people. Tests
soon revealed that the disease was a new variant of C.J.D. that could be traced
directly to eating cattle infected with mad cow disease.
In recent months, researchers have discovered that a prion from hamsters, thought
never to infect mice, not only replicates profusely in mice but it does so without
producing disease symptoms. In other words, mice can be silent carriers of a
disease that originated in hamsters. When subsequent generations of mice are
exposed to blood or nervous tissues from silent carrier mice, they get the disease.
Other experiments carried out in the United States show that the deer or elk prion
in chronic wasting disease can convert healthy human prions into infectious
prions in test tubes. The conversion rate is slow but certain.
The best available science shows that chronic wasting disease can infect human
tissue but wildlife officials are carrying on with "business as usual," said Dr. Tom
Pringle, a biologist in Eugene, Ore., who closely follows T.S.E. worldwide and
independently studies the disease.
"Who'd want hamburger from a cow where 15 percent of the herd had mad cow
disease?" Dr. Pringle asked. "Who'd want mutton from a sheep where 15 percent
of the sheep had scrapie? To me it looks like Russian roulette for hunters."
Most Americans don't understand how dangerous these diseases really are, Dr.
Pringle said. It is extremely difficult to kill infectious prions that have come into
contact with surgical instruments, yet some hunter who is "tired, cold, hungry and
drunk" will cut off a deer head, handle the animal's spinal cord and "stick his
hunting knife back into his scabbard," he said. That knife could spread disease.
Dr. Pringle strongly criticizes wildlife officials as downplaying the seriousness of
chronic wasting disease. Just as British agricultural officials initially acted to
protect the image of the cattle industry — one even fed hamburger to his
4-year-old daughter on television to prove beef was safe — American wildlife
officials are acting to shield hunting and fishing, he said. Fishing and hunting
license fees provide a substantial portion of their agencies' income.
But Dr. Elizabeth Williams, a veterinarian at the University of Wyoming in Laramie
and a leading researcher on chronic wasting disease, said that hunters are not
going to be deterred until there is much better evidence that chronic wasting
disease in deer and elk is a danger to people. The prevalence and incidence of
chronic wasting disease has not changed much over the past several years, she
said. And it is still not known how one animal passes the disease to another, much
less if humans face more than a theoretical risk.
Hunters, many of whom come from other states, are given a 54- page brochure that
describes chronic wasting disease, Dr. Miller said, and on page 9 they are advised
to avoid coming into contact with brain, spinal cord, eyes, spleen or lymph nodes
of any deer or elk they might kill. The brochure states that "it is unlikely that
chronic wasting disease is naturally transmissible to humans."
Nevertheless, some Colorado wildlife officials have suggested killing 50 percent of
the deer in the north- central part of the state where more of the deer are infected,
Mr. Hale said. "They want to kill them and start over," he said. But he added that
they do not think the disease threatens hunters. "It would have shown up by
now" in people, he said.
On Saturday, Mr. Zunker went elk hunting about 15 miles from his home not far
from the state border, an area where rates of chronic wasting disease are high.
"I talked to a game warden the other day and he didn't mention anything to me
about a problem in that area," he said. "I don't get overly concerned. I don't know
if Game and Fish have done a good job of informing the public. But if it's a true
threat, how come they haven't reduced hunting quotas?" |
