- "...people may carry [CWD and related] diseases
without knowing it."
-
- The deer is terrified at the sight of trees. Although
it has long lost its appetite for food, it gulps water madly. Soon, after
more bizarre behavior, it will die.
-
- Its problem is not mad cow disease -- but it's close.
It's chronic wasting disease, a North American sibling of mad cow that
infects wild deer and elk across northern Colorado and southern Wyoming.
In the past two years, it has leapt as far as New Mexico and Wisconsin,
and is expected to continue spreading.
-
- Oregon officials regularly test wildlife for signs of
the scourge, which can dwell unnoticed in its victims for years before
escalating to symptoms and then death.
-
- U.S. researchers are trying to unravel the disease, and
as they do they shed new light on its relatives, including mad cow disease
-- high on the nation's radar since appearing in a lone dairy cow in Washington
state.
-
- Studies show, for instance, that diseases thought to
be caused by malformed proteins called prions may be versatile killers
-- capable of morphing in form and virulence while moving from one species
to another. They may seem to disappear in one carrier only to reappear
and renew their deadly spree.
-
- Such behavior could help them elude standard testing.
-
- Research at a federal laboratory in Montana suggests
more people in the United Kingdom may carry bovine spongiform encephalopathy,
or mad cow disease, than the more than 140 who died from it.
-
- "In Great Britain, we think it could be true that
many more people may be carriers than we know about," said Rick Race,
a research veterinarian at the Rocky Mountain Laboratories, a branch of
the National Institutes of Health in Hamilton, Mont.
-
- Still, none of the brain-wasting diseases, known together
as transmissible spongiform encephalopathies, or TSEs, relinquish their
secrets easily. But studies of some offer clues about others.
-
- There is no evidence chronic wasting infects humans,
while there is also no proof it cannot. Epidemiologists searched unsuccessfully
for links between it and three deer and elk hunters tied to Washington
state; they died from 2001 to 2003 of Cruetzfeldt-Jakob disease, an illness
thought to be caused by the same sort of prions.
-
- It strikes roughly one person in a million, and there
was no sign the deaths were anything more than random chance.
-
- No one is sure how chronic wasting spreads. It may be
through contact among animals or infected feces and saliva. It kills some
animals but not others. It infects some species at a greater rate than
others.
-
- No known cure Authorities, meanwhile, do not recommend
against eating wild deer and elk. But they advise hunters to avoid animals
that appear sick, and to wear latex or rubber gloves while dressing carcasses,
and minimize the handling of brains, spinal cord and other parts where
the disease could be concentrated.
-
- There is no known cure for chronic wasting. Even the
precise cause is mysterious.
-
- "We have to realize, we may not ever know everything
about these diseases," said Elizabeth Williams, a professor of veterinary
sciences at the University of Wyoming.
-
- Oregon wildlife authorities have been on guard for chronic
wasting since 1996, when they started testing brain tissue from a few deer
and elk that seemed ill, said Don Whittaker, a wildlife biologist with
the Oregon Department of Fish and Wildlife.
-
- They started to widen sampling in 2001, checking animals
killed by hunters and on highways. About 1,900 elk and deer have now been
tested for about $25 each, underwritten by federal funds and donations
from the Rocky Mountain Elk Foundation and Oregon hunting groups, Whittaker
said. None had the disease.
-
- About 100 additional tests are pending.
-
- Officials have not inspected enough Oregon animals to
say definitively that Oregon is free of the disease, although there is
no reason to suspect otherwise, Whittaker said. It may take infected animals
three or more years to become ill. Chronic wasting spreads slowly at first,
before accelerating.
-
- Disease appeared in the 1960s
-
- "It's difficult to predict," he said. "There's
a lot of unknowns with the whole complex of TSEs."
-
- Chronic wasting was first recognized in captive deer
in Colorado in the 1960s. Many scientists suspect it is descended from
scrapie, a brain-destroying disease in domestic sheep. Others think it
might arise spontaneously from time to time, possibly from a random genetic
mutation.
-
- By the 1980s, however, researchers realized it infected
free-ranging deer and elk, too. They suspect shipment of infected animals
between game farms in Colorado and other states helped spread it to 12
states and two Canadian provinces, according to the Chronic Wasting Disease
Alliance, a coalition mainly of hunting groups.
-
- Thousands of wild and captive animals have been slaughtered
to try to stifle the disease.
-
- Oregon has banned all importation of captive deer and
elk, Whittaker said. Hunters cannot bring a deer or elk carcass into Oregon
from a state where chronic wasting disease is known to exist unless the
brain and spinal column are removed.
-
- Scientists working with mice, hamsters and monkeys at
the Rocky Mountain Laboratories have made disconcerting findings about
the mysteries surrounding chronic wasting and related diseases.
-
- Just as humans do not appear to be at risk from scrapie,
they figured mice were not susceptible to a strain of scrapie that infects
hamsters. As a check, they gave hamster scrapie to mice. None got sick.
-
- Point proved? Not so fast.
-
- "Every hamster died" "For the heck of
it," they injected bits of the mice brains into healthy hamsters,
said Rick Race, a research veterinarian at the laboratories. What happened
next surprised them.
-
- "Every hamster died."
-
- The result told scientists that although the mice showed
no sign of illness, they harbored the disease. If mad cow and chronic wasting
behave the same way -- which is unknown -- they might dwell where no one
expects them. Even people may carry such diseases without knowing it.
-
- Then Race and his colleagues injected additional mice
with the infectious agent. Those mice slowly fell ill from the same hamster
disease the first round of mice had resisted.
-
- Given time, the agent had somehow adapted to destroy
its new host.
-
- "The scrapie seemed to have learned how to deal
with this new species, and it worked much better," Race said. "It
replicated faster in additional rounds of mice and even became more lethal
to them."
-
- It suggests that tissue moved from one species to another
may have unintended consequences. That means livestock industry practices
of feeding animals byproducts of other animals could be risky, researchers
say.
-
- Now that it's clear prion diseases can jump from species
to species, "and because we've shown that this process is slow and
difficult to detect, it may be time to rethink this practice," Race
said.
-
- What remains puzzling is that the prions thought to cause
brain-wasting diseases are proteins -- rudimentary material with no genetic
code, no more alive than rocks. So how can they evolve to attack a brand
new species? No one is sure.
-
- Some scientists suspect prions may be somehow driven
by still-unknown viruses that resist the high heat and pressure that destroys
more familiar viruses.
-
- Scientists at the laboratories have devised test tube
experiments to predict which wasting diseases could leap from one species
to another. They show the likelihood of mad cow and chronic wasting moving
to humans is low.
-
- To further check that, Race and his colleagues are waiting
to see if monkeys exposed to chronic wasting develop the disease.
-
- - Michael Milstein: 503-294-7689;
- michaelmilstein@news.oregonian.com
-
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