Wasting disease hits state's deer
By Michael Booth and Theo Stein
Denver Post Staff Writers
Feb. 4, 2001 - A fatal brain-wasting disease has animals
staggering on four hooves, glassyeyed and slobbering.
Government doctors conduct intensive
research, acknowledging that what they
don't know about the mysterious disease
exceeds what they do know.
National media suggest that a horrific
human health threat is being soft-pedaled
by medical and wildlife authorities, leaving
an edgy public unsure how to react to
each new rumor.
Sound familiar? But it's not a tale from
far-off Europe, where "mad cow disease"
has shattered the beef industry and
paralyzed the continent with fear.
It's the current state of affairs
concerning a "mad deer disease" that has
struck wild deer and ranched elk in
certain parts of the Rocky Mountains,
leaving health officials scrambling to
assess the possible threat to humans.
For now, Rocky Mountain veterinarians,
wildlife experts and public health officials
stress that there has never been a
confirmed case of humans becoming sick
from the deer illness, which is called
chronic wasting disease. And they add
that all of the research on the deer
disease suggests the risk to humans is
exceedingly low, even as inaccurate
stories of human cases mistakenly linked
to consumption of allegedly infected
venison are recycled in the media.
"The only thing that seems to be
spreading rapidly is misinformation in the
popular media," said Mike Miller, a wildlife
veterinarian with the Colorado Division of
Wildlife. "And that should certainly be a
cause for concern."
Chronic wasting disease is one member of
a family of always-fatal diseases called
transmissible spongiform
encephalopathies, which essentially turn
a victim's brain to mush. In cows, the
variety is called bovine spongiform
encephalopathy, or mad cow disease.
The human form is Creutzfeldt-Jakob
Disease, or CJD, which strikes the elderly
as a spontaneous mutation in about one
in a million adults.
Little is known about the infectious agent
that causes both chronic wasting and
mad cow disease. What is known is that
common proteins called prions change to
a renegade, lethal form. But researchers
are struggling to understand how those
bad prions convert others to cause the
virulent diseases.
"The main problem with this issue is that for several of the most
important questions, we don't have any scientific-based answers,"
said John Pape, an epidemiologist with the Colorado Department of
Public Health and Environment.
Chronic wasting disease was first discovered at Colorado State
University in 1977, but researchers think it existed in wild
populations for at least 40 years. It is now focussed in a
15,000-square-mile area of northeast Colorado, southeast
Wyoming, and a small portion of the Nebraska panhandle. A parallel
epidemic is working through captive elk on ranches in South
Dakota, Montana, Wyoming and several Canadian provinces. Last
week, Oklahoma officials announced they would slaughter 140
quarantined elk, after five members of a herd died of CWD. The
herd came from Montana.
Researchers don't yet know how deer or elk pass it to each other.
They do know, however, that the leap from deer or elk to a human
illness is a long and difficult one.
First of all, the rogue prions concentrate in brain tissue and spinal
cords, not in the cuts of meat most humans consume, said Dr. Ken
Tyler, a professor of neurology at the University of Colorado Health
Sciences Center. In fact, tests have never identified the infectious
prion in muscle tissue.
Moreover, eating the tainted material further cuts the chances of
transmission, because the digestive system destroys many
diseases. Finally, the disease has to cross the species barrier, from
beef or venison to humans.
"It is not impossible," Tyler said, citing the 100-odd cases of mad
cow disease now having spread to humans in Britain. "But it is not
a very efficient spreader."
While scientists are working hard to avoid the kind of mass herd
slaughter and consumer panic sweeping Europe as a result of mad
cow disease, they also say the threat of chronic wasting disease
among deer and elk has to be put in the context of other risks to
human health.
"Hunters should quit smoking first, and then get their deer heads
tested," Tyler said. "If I had a choice in patients of a hunter who
stops eating venison and a hunter who promises to quit smoking
and wear his seat belt, I'd rather have the second one." A relief for
the wary researchers is that so far chronic wasting is behaving
very differently from Europe's mad cow disease.
In England, the practice of feeding cows protein supplements made
from rendered animals allowed the mad cow agent to infect entire
beef herds. Continued recycling of the infected tissue - a kind of
forced cow cannibalism - magnified the problem, leading to the
slaughter of hundreds of thousands of suspect cattle in England in
the early '90s before any human crossover was identified. Despite
the tough measures, researchers still had to wait to see whether
the disease would cross into humans who had eaten infected beef.
The waiting ended in 1996, when British officials said they had
found a new variant of CreutzfeldtJakob Disease caused by beef.
As soon as the first cases appeared in Europe, U.S. health officials
started worrying, too. While U.S. laws prevent using rendered
animal protein in animal feed, an untold number of Americans had
traveled overseas and might have consumed the same beef. So
far, no cases of the mad cow variant have been found in either
humans or cattle in the United States.
Last year, attention shifted as the Centers for Disease Control and
Prevention investigated the deaths of three U.S. citizens, far
younger than the usual victims of Creutzfeldt-Jakob, who either
hunted or ate venison regularly. After extensive post-mortems, all
of the patients were shown to have died of the common form of
the disease, not the new variant caused by food, said Dr. Ermias
Belay of the CDC in Atlanta.
When mad cow disease crossed over, British health officials
identified several traits in the human victims: Their youth, their
symptoms and the physical effect on their brains all differed from
the long-known, spontaneous form of Creutzfeldt-Jakob.
But in the three U.S. deaths the CDC has investigated, there was
no evidence that the individuals died of anything other than the
spontaneous common form. In fact, the most compelling
arguments, Belay said, point away from chronic wasting disease.
"The most significant evidence to us is the cases didn't even have
the opportunity to be exposed to venison potentially contaminated
with CWD," said Belay. "None of them consumed deer or elk meat
from the known endemic areas in Colorado and Wyoming."
Belay said researchers then turned their attention to areas where
victims had obtained deer. In collaboration with federal agriculture
officials, the center sampled tissue from 1,000 deer and elk
carcasses, and none tested positive for chronic wasting disease.
Colorado and Wyoming have issued reasonable and safe guidelines
for hunters in their area, Belay said. If people want to protect
themselves further, they can avoid consumption of deer brains and
spinal cord, no matter where the animals are harvested.
A key for researchers is their assumption that some people have
already eaten meat tainted with chronic wasting disease, yet no
crossover cases have been proven.
"No one can tell you that will never happen," he said. "But is it
causing disease in humans right now? No, it is not. Every test we
have done suggests it is not transmitted to humans."
In 1996, the CDC established the National Prion Disease Pathology
Surveillance Center at Case Western Reserve University in
Cleveland to look for cases. In Colorado, state epidemiologist Pape
also monitors traditional CreutzfeldtJakob cases, looking for
patterns.
If any victims under age 55 are reported, the federal center follows
up.
