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From: TSS (216-119-144-70.ipset24.wt.net)
Subject: CHRONIC WASTING DISEASE MOVING ON
Date: October 26, 2004 at 12:50 pm PST
-------- Original Message --------
Subject: CHRONIC WASTING DISEASE MOVING ON
Date: Tue, 26 Oct 2004 14:53:39 -0500
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy
To: BSE-L@UNI-KARLSRUHE.DE
##################### Bovine Spongiform Encephalopathy #####################
CHRONIC WASTING DISEASE
MOVING ON RESEARCHERS CONTINUE TO PROBE THE NATURE
OF THE DISEASE, WILDLIFE MANAGERS LOOK FOR
WAYS TO CONTROL IT WHILE HUNTERS AND OTHER
CONSERVATIONISTS ASK HARD QUESTIONS.
ARTICLES BY CHRIS MADSON, TIFFANY MEREDITH,
TOM REED, AND MICHELLE ZITEK
PHOTOGRAPHY BY TIM CHRISTIE, CHRIS MADSON,
LURAY PARKER, AND BETH WILLIAMS
ANSWERS… AND QUESTIONS
Article by Chris Madson
Wildlife diseases have a way of going unnoticed. A deer or a dickey bird
picks up an infection, starts feeling
draggy, and repairs to some secluded hiding place to heal. If the
patient recovers, he’s back in circulation within days, if he
expires the coyotes and buzzards clean him up, leaving little evidence
of the cause of death. Either way, a disease outbreak
can go years without being noticed, even if the illness itself is well
known. If the disease is something new to science, it
can do an even better job of hiding.
Which is why chronic wasting disease has been such an enigma. Nobody
knows for sure where CWD started.
Researchers first recognized it in the late 1960’s. Some of the captive
mule deer in a wildlife research facility near Fort
Collins, Colorado, seemed to be starving, even though they had plenty of
food. Affected animals became emaciated and
listless; their ears drooped; they drooled and seemed constantly
thirsty. Within months, they dropped dead.
The cause of this pattern of illness wasn’t known until Beth Williams, a
veterinary graduate student at Colorado
State University, decided to look at tissue samples from the brains of
the dead animals. The tissue was shot through with
microscopic holes, a tiny version of a kitchen sponge.
Williams recognized the pattern. This was one of a group of diseases
called "transmissible spongiform
encephalopathies." "Transmissible" because they spread from one victim
to another. "Spongiform" because they leave brain
tissue looking like sponge. "Encephalopathy" because they are diseases
of the brain.
TSEs are a relatively rare group of diseases. Probably the most common
is scrapie, a sheep disease that was first
described in Europe more than 200 years ago. Transmissible mink
encephalopathy is occasionally found in ranched mink.
Each of these diseases seems to be species-specific in normal
circumstances-cats don't catch mink encephalopathy;
shepherds don't catch scrapie.
Bovine spongiform encephalopathy - or mad cow disease - appeared in
British cattle about twenty years ago. Up
until the late 1980s, feed producers in Britain used parts from dead
animals to boost protein content in their products.
Apparently, animals that had died of disease were sometimes used as
protein supplement. Scientists who have studied BSE
think sheep that had died of scrapie were used for cattle feed,
eventually allowing the sheep disease to jump the "species
barrier" from sheep to cattle.
There are also a few human TSEs all of them very rare: fatal familial
insomnia, kuru, Gerstman-Straussler-
Shenker syndrome, Creutzfeldt-Jakob and variant Creuzfeldt- Jakob
disease (vCJD). Kuru was spread from one member of
New Guinea's Fore tribe to another when the men participated in the
ritual cannibalism of a deceased relative. Fatal familial
insomnia and Gerstman-Straussler-Shenker syndrome are apparently passed
down through families genetically. CJD occurs
in about one in a million humans and is not ordinarily transmissible.
Variant CJD developed in 136 people in Europe,
mostly in the United Kingdom, over the last eight years after hundreds
of millions of people ate meat that contained brain
or spinal cord from cows with BSE.
What causes TSEs? There is still some debate. A few scientists believe
the culprit is an extremely simple, slowacting
virus. However, an extended search has failed to find either the viruses
or evidence of the RNA or DNA from a
phantom virus. Most of the scientists who have studied TSEs think these
diseases are caused by a whole new group of
pathogens. They are rogue proteins called prions.
Normal versions of these proteins are found in the membranes of cells,
primarily in the nervous system. Their
function is unknown. Apparently, it's possible for these proteins to
change form, although they do so very rarely. The
altered form of the protein doesn't break down easily, and because of
its different shape, it disrupts the structure of the
tissue it occupies.
One infectious protein or "prion" would have negligible effect, but a
prion can cause a normal protein to shift its
shape so that it becomes a prion as well. Prions aren't alive in any way
we understand the term, so they don't reproduce.
Instead, they convert existing benign proteins to the damaging prion
form. Eventually, the change in billions of protein
molecules rips tiny holes in the brain, causing death.
It's tempting to assume that chronic wasting disease began out of
nowhere in the Fort Collins research pens or on
the Wyoming Game and Fish Department's Sybille Wildlife Research Unit in
Southeastern Wyoming. Analysis of the
infection rates in wild deer and elk along with mathematical modeling
suggest that the Fort Collins area may, in fact, be one
focus of infection, but deer from the Colorado research facility were
routinely moved to Sybille and vice versa. The
Wyoming research pens seem to be another long-term focus of infection.
All the research deer tract their lineage back to
the wild, so there is some chance that the disease was brought into the
research units. Speculation on the source of the
disease is easy to find, but it’s likely that no one will ever know for
sure how or where CWD started.
Efforts to sterilize the research pens in Wyoming and Colorado didn't
succeed, suggesting that the CWD prion
doesn't break down readily in the environment and can survive outside an
animal's body for a year or more. When
apparently healthy deer or elk are released on sites that have supported
large numbers of infected animals, the healthy
newcomers often develop CWD.
So far, there is no way of testing for prions outside of animal tissue,
which means that researchers can't look for it
in soil, water, or feed. That makes it hard to figure out how CWD makes
its way from one animal to another. The best guess
now is that the disease usually spreads by direct contact between two
animals and/or possibly through feces, and ingestion
with food. Colorado researchers have found that some of the highest
infection rates among deer are found in herds that
people routinely feed.
Experience with CWD in captivity indicates that, once a deer develops
signs of the disease, it will die. The body
doesn't seem to mount any sort of immune reaction, probably because the
prion is so similar to other proteins. Elk seem to
be more resistant to CWD than deer, and some research suggests that the
elk that do die of the disease may have the same
genetic makeup at one site on their chromosomes. This leads to a faint
hope that a few elk in the wild could have a genetic
resistance to CWD. At this point, no one knows for sure.
Disease specialists have been tracking the incidence of CWD in Colorado
and Wyoming since the early 1980s. As
a general rule, the proportion of infected animals is highest where a
disease begins and has been present the longest-
infection rates drop off in areas where a disease has just spread.
The proportions of CWD-infected deer seem to indicate that the outbreak
in Wyoming and Colorado began in the
Fort Collins area and around the Sybille wildlife research center west
of Wheatland, Wyoming.
The disease seems to be spreading in the wild, but even this spread is
open to some question. Until five years ago,
there was no intensive effort to test for CWD outside of Wyoming and
Colorado the animals that were positive came either
from captive herds or were killed in the wild because they looked sick.
As testing for the disease has expanded, more
CWD-positive deer and elk have turned up in places farther and farther
from the original areas of infection. This is probably
because the disease has spread, but it may also have something to do
with the intensified testing itself.
In the wild, CWD now occurs in most of northcentral Colorado, south
eastern Wyoming, and the western edge of the Nebraska panhandle. A dozen
CWD-positive deer and elk have turned up in South Dakota's Black Hills, and
several positive deer have been found in eastern Utah near Vernal,
northeast of
Moab, and southeast of Salt Lake City. Biologists in Wisconsin have found
hundreds of positive white-tailed deer in the southwestern part of the
state, and
several have been taken in northcentral Illinois. Saskatchewan also has
CWD in
wild deer, and it has been identified in a small herd in southern New
Mexico.
In addition to CWD in wild deer and elk, there have been many cases
reported in farmed deer and elk. At last report, nine states and two
Canadian
provinces had CWD in captive deer or elk- seventy-three herds in all. The
infections in these herds could have been introduced to the wild in
places like
Saskatchewan, Nebraska, and Wisconsin.
This is what we think we know about chronic wasting disease. Crucial
questions remain unanswered. How does CWD spread? How long can a CWD
prion persist outside the body of a living animal? How can we identify the
prion in the physical environment? Do some deer and/or elk have a genetic
resistance to CWD? Are there tests for CWD that can be done quickly and
inexpensively on wild animals? Is there a practical way to immunize animals
against CWD?
Researchers are already straining to find the answers to these and other
questions concerning chronic wasting disease. The pace of the work is con-
trolled, as always, by the funds that are available. While we spend more
money
on dealing with CWD, we should make sure we spend more trying to
understand it.
A deer may suffer from chronic wasting disease for several months before
obvious symptoms begin to show. Near the end,
an infected deer may show a rough disheveled coat, drooping ears, a lack
of interest in its surroundings, excessive thirst,
and a tendency to drool. At this point, death is certain, often in a
matter of days. (Photo by Chris Madson)
CWD’s IMPACT ON DEER HERDS - -article by Chris Madson
As far as we know, chronic wasting disease is 100 percent fatal- no one
has ever seen a deer or elk recover from
infection with CWD. If CWD passes readily from one animal to the other-
and it seems to do that - then it could take a huge
toll on a deer herd. If the prion persists in the environment for a long
period of time- and it seems to do that- then recovery
of a deer herd could be slowed.
While deer managers try to contain CWD a few specialists in wildlife
disease have been trying to figure out how it
will affect deer populations in the wild. This can be a difficult
exercise. It's difficult to count deer in the wild, even with
modern techniques like aerial transects and sophisticated computer
modeling. And many forces impinge on deer herds.
Over the last eight to ten years, a prolonged drought in much of the
West has taken a toll on deer that is hard to quantify.
In an effort to predict what might happen to a deer herd infected with
CWD, several disease specialists have used
what we think we know about CWD to build a computer model. The model
starts with a deer herd of a given size, then adds
or subtracts deer for various reasons. Deer are added during simulated
breeding seasons. They die as a result of simulated
hunting seasons; the effects of winters; the toll claimed by predators,
other accidents, and disease. The model considers the
mortality rate in CWD-infected animals, the rate at which the disease
might spread, the lag between the time an animal first
catches the disease and the time that same animal can infect other animals.
All of these gains and losses can be adjusted, allowing the researchers
to consider the effects of all the variables.
The next step is to get some sort of estimate of the range of gains and
losses in real deer herds. With those numbers in hand,
the researchers can set up a digital deer herd and follow its ups and
downs through fifty or 100 years. Clearly, no model can
be as complex as the interaction between real deer and a constantly
changing environment, so the estimates any model
makes are a rough estimate at best. The performance of the model also
depends on the accuracy of the data fed into it,
another source of distortion. Still, with all their shortcomings, models
can be useful in testing our assumptions about deer
losses to disease and other mortality.
After fine-tuning the model, the researchers ran 250 simulated deer
herds through the computer. The graph, shown
below is an average of those simulations. The top line shows a century
of fluctuations in the population of a theoretical deer
herd of 1,000 animals without CWD. The centerline shows the change in
250 simulated deer populations infected with
chronic wasting disease. The bottom line shows the change in the number
of CWD-infected animals at any given time.
The model's predictions are
sobering. In the first twenty years, the
disease spreads through the simulated
herd, but it has little effect on the over- all
population. As the number of infected
animals increases, however, the population
begins to fall. Thirty years into the
simulation, the average population has
dropped about ten percent. Fifty years out,
the population has been cut in half, and at
the end of the century, it has dropped by
ninety percent. In many of the simulations,
the deer herds were wiped out.
(Of course, wiping out an
infected deer herd has its advantages- if it
can be done before the disease spreads, the
disease provides for its own extinction,
assuming, of course, that the disease
pathogen can't survive outside a deer.
Unfortunately, CWD takes months to kill
a deer, allowing an infected animal to
spread the disease to other members of its herd or to animals in other
herds. And the CWD prion seems to persist for long
periods in the environment. If that's the case, a local deer herd could
disappear, and the disease could still find its way into
new animals moving into the unoccupied habitat.)
The model gives us one other piece of information. By considering the
change in the proportion of animals that are
infected, the model can give an estimate of when the CWD started in the
herd. According to the researchers, "chronic
wasting disease probably has been occurring in captive deer for more
than 30 years."
According to this modeled view of CWD, some of the infected herds in
Colorado and Wyoming should be
showing some signs of decline. Since Colorado has increased harvest and
done some selective culling on the deer in CWDinfected
areas, the populations have already been reduced, and the effect of CWD
on numbers may be camouflaged.
Colorado has experimented with herd reduction as a way of controlling
CWD, but Wyoming hasn't. The number of permits
issued for deer in southeastern Wyoming has changed through the years as
the populations have ebbed and flowed, but
there has been no effort to reduce deer numbers drastically with
expanded hunting seasons or professional gunners.
The graphs
presented here show
population estimates for
three deer herds in
southeastern Wyoming. The
Iron Mountain herd is found
from the Colorado state line
north to Sybille Canyon west
of Wheatland, Wyoming.
The Laramie Peak herd
ranges from Sybille Canyon
north into the country west
of Glendo and Esterbrook.
The north Converse herd
uses the high plains and
breaks from Douglas and
Casper north to the towns of
Wright and Midwest.
The Iron Mountain
and Laramie Peak herds may
have had chronic wasting disease as long as it has existed. Sybille
Canyon, the border between the two herd units, is home
to the Sybille Wildlife Research Center, one of the two research
facilities where CWD was first identified. The north
Converse herd lives near these two herds in country that has about the
same elevation and weather, but north Converse deer
have only recently been infected with CWD.
It's hard to see any difference between the population trends, even
though there is reason to believe that the Iron
Mountain and Laramie Peak deer may have had CWD, for more than thirty
years. And the three graphs have yet to show a
good fit with the population trends predicted by the CWD model.
There may be several possible reasons for the disparity. First, the
population estimates for the herds are not precise
because it is almost impossible to get a precise count of wild deer.
Second, we don't know for sure how long CWD has been
in the wild in southeastern Wyoming- we may still be in the first few
years of the model before the declines show
themselves. Third, the deer in these herd units aren't confined by any
impassable barriers. It's possible for deer to move into
these herds from nearby areas, masking a population decline.
It's also just possible that these herds aren't responding to CWD as the
model predicts. If that turns out to be the
case, it suggests that one or more of our assumptions about chronic
wasting disease may be flawed. Another ten or fifteen
years of routine big game census will give us a much better picture of
the population trends in these CWD areas. At this
point, the model and the real-world population estimates tell us the
same thing: The list of things we don't know about
CWD is a lot longer than the list of things we know for sure.
MANAGING CWD - article by Tiffany Meredith
Since chronic wasting disease was discovered in the wild in March 1981,
wildlife officials have been faced with a
dilemma: how to manage a disease about which so much is unknown.
Biologists don't know what kind of long-term impact the disease will
have on wild populations of deer and elk.
Researchers aren't sure how the disease is spread, although they know it
can be transmitted from animal to animal.
While the number of cases has gone up recently, it's not clear if that
is because more animals are infected or
because officials are looking harder for the disease.
They are. The first line of attack, at least for now, is to pinpoint
where chronic wasting disease exists through
intensive surveillance. In Colorado, Nebraska, and Wisconsin, officials
are going a step further by thinning herds and
reducing the number of animals in "hot spots," or areas with a high
number of cases, in an attempt to put the brakes on the
disease's spread.
Officials believe the disease is spreading, but slowly. Until 2000, CWD
was known only to exist in the wild in
northeast Colorado and southeast Wyoming, which found its first wild
case in an elk in 1986. CWD now also exists in the
wild in Nebraska, South Dakota, Utah, New Mexico, Wisconsin and Illinois
and in Saskatchewan.
Surveillance began in Wyoming in the early 1980s. The first documented
wild case was a sick elk found by
biologists in Rocky Mountain National Park that was determined to have
CWD. Surveillance is now going on throughout
the U.S. and in Canada.
CWD also has been found on game farms in Colorado, Nebraska, South
Dakota, Wisconsin, Minnesota, Kansas,
Oklahoma, Montana, Saskatchewan and Alberta. Most of these captive herds
have now been depopulated because of the
presence of CWD.
Culling of wild deer, which may be more susceptible to CWD than elk, has
generated some controversy from the
public over whether the action is warranted based on what officials know
about the disease. But Colorado Division of
Wildlife officials point to long-term modeling done in conjunction with
Colorado State University that shows deer
populations in northeast Colorado, where the disease has been
established for decades, could eventually be reduced
dramatically if CWD was left to run its course. "In areas where we find
an unusually high prevalence of the disease, the
best tool we have is to remove those animals with the disease or those
that have been exposed," said Todd Malmsbury,
public information chief for Colorado's wildlife division. "By removing
these hot spots of infection, we believe we can
slow the spread of the disease and reduce the prevalence."
Since chronic wasting disease doesn't kill an infected animal quickly,
there is a chance for a sick deer or elk to move long
distances and gather with large wintering herds where the infection can
spread. (Photo by LuRay Parker)
Culling in Colorado has been done only in the northeast. Many times
those hot spots are associated with urban
areas, where deer are protected and unnaturally numerous, and where they
are sometimes illegally fed by the state's
burgeoning Front Range human population, which enjoys watching them. The
division also has cracked down on those who
don't obey the ban on feeding.
"While there's no absolute connection, there's some suggestion that
feeding concentrates deer and elk and
contributes to the problem, " said Mike Miller, Colorado Division of
Wildlife veterinarian and a leading CWD researcher.
"It brings them back to the same place day after day and congregates
them, which is not normal in free-ranging animals."
As the disease takes two to three years to claim its victims, it's too
early to tell if the culling strategy is working.
"These animals were probably infected before we started our management
efforts," Miller said.
"We need data to look at over several years. We've been managing in
earnest for only about two years, and it'll be
about five years before we could really see a positive response. It
would be a pleasant surprise to see a reduction in CWD
now."
Wyoming, however, has opted not to cull herds, instead focusing on
finding out where exactly the disease occurs
in the state.
Officials have expanded surveillance from the southeast area statewide
this year, prompted by cases found in other
states outside the area where the disease was known to exist.
"It may be elsewhere, but we might not have looked hard enough," said
Wyoming Game and Fish Department
wildlife veterinarian Terry Kreeger. "We're probably going to delay
management efforts we might take until we find a new
case in a new spot some distance from the southeast."
Right now, Kreeger said that known cases appear to be a natural
extension of the disease, although two cases some
distance from the established area are being investigated.
A new case in Saratoga will be the Game and Fish Department's first
attempt at management. "When we find one new
case, we'll sample about twenty to thirty animals to see if there are
any more cases to determine if it's an isolated one or
more widespread," Kreeger said.
"If it's two to three cases, we might widen the area where we culled
deer to see if we find more. But if we find
seven to ten cases, we might decide not to do anything more because this
would suggest that CWD was well established."
Game and Fish hopes to collect about 6,000 samples from hunter- killed
animals, this year to better understand the
distribution of the disease. Last year, the department looked at 2,550.
"If we're really lucky, we might not find CWD anywhere else and might
not do a statewide surveillance again for a
couple of years," Kreeger said. "The biggest key to the ultimate
management and control of the disease is to understand
how it's spread from one animal to another. We understand a lot about
bacteria and viruses, but don't understand how this is
spread.
"Then we might develop management tools to break the train of transmission."
Like Wyoming, Colorado's goal is to get precise location information
about CWD. Last year, the Division of
Wildlife looked at over 27,000 samples.
"Our goal over the next few years is to survey all deer and elk
populations statewide," said Miller. "We hope to
build our sample size and fill in gaps to get a complete picture of
where the disease is and where it is not."
Colorado also is thinning herds with longer hunting seasons for mule
deer in the northeast part of the state, with
increased licenses and with special licenses to control populations of
deer and elk in problem spots. In Nebraska, chronic
wasting disease turned up in 2000 in the extreme southeast corner of the
panhandle near Kimball, although the state had
been monitoring for the disease since 1997.
The state has now expanded its surveillance and also is thinning herds,
said Bruce Morrison, assistant
administrator for wildlife for Nebraska Game and Parks.
"We're doing our best to reduce deer density with expanded hunting,"
Morrison said.
The state currently is trying to secure federal funding for a study to
determine social interaction and movement of
deer in infected areas through radio collaring.
Wisconsin has taken arguably the most aggressive stance since the
disease was found in its southwest corner in
February 2002. The department has succeeded in lowering the population
in known infected areas with high harvest on
antlerless animals, including summer seasons of one week per month last
summer and extending gun seasons from the
traditional nine days to late October through January.
The state continues to sample every deer harvested in the CWD area, and
is using focused thinning in areas where
it knows the infection is present, said Andy Nelson, an area wildlife
supervisor with the Wisconsin Department of Natural
Resources.
"We're mapping exactly where the problem exists and at what level,"
Nelson said. "Then we'll shape our CWD
management where the sick animals are."
Through sampling, the department has found ninety confirmed locations,
and believes there are no other infected
areas.
"I think it's fair to say we've done a good job of finding out where the
disease occurs, where it doesn't and
documenting the degree of occurrence," Nelson said.
Landowners in infected areas also were offered free deer licenses with
an unlimited bag but had to "earn a buck"
by killing a doe first.
Nelson said the move was effective in increasing the harvest, but
"there's still a significant number of deer within
the infected area.”
"It remains to be seen if there's a strong enough desire from the public
to eliminate the herd and the disease along
with it."
This year, the department will continue to solicit heads from hunters in
and around known infected areas.
Wisconsin also has a goal of getting a large number of deer
systematically across the state to complete the statewide
surveillance.
"We are going to continue to take the pulse of health of the herd,"
Nelson said. "The zone has gotten bigger as we
find more positive cases. The size of the problem area doubled this
year, though the original hot spot herd was reduced."
In addition to efforts by states, the federal government has taken steps
to control CWD. In May 2002, Congress
directed the Department of Agriculture and the Department of the
Interior to come up with a plan to help state wildlife and
agriculture agencies manage CWD and to coordinate federal and state efforts.
Interstate movement of deer and elk from game ranches is managed by the
USDA, which will ban importation of
animals from states where the disease had been detected. In Colorado and
other states, entire commercial game herds have
been purchased by the USDA and destroyed and incinerated, as some
believe the movement of commercial elk from one
ranch to another across state lines spreads the disease. In
Saskatchewan, all game farms are required to be enrolled in a
CWD monitoring program.
"Much of our work is adaptive to the rapidly increasing knowledge about
CWD," said Colorado's Malmsbury. "It
was first noted by Beth Williams (at the University of Wyoming) in the
1970s, and in terms of understanding the disease
and management, that's a relatively short period of time."
NEW RESEARCH - article by Tiffany Meredith
In the fight against chronic wasting disease, Wyoming and Colorado are
on the front lines. As wildlife
management agencies, public health officials, hunters and the beef
industry struggle to understand the mysterious infection,
studies under way in the two states could eventually provide answers.
"We want to know how it's transmitted, how the (disease) agent might be
shed and what the fate of it might be in
the environment," said Beth Williams, a professor of veterinary science
at the University of Wyoming in Laramie and one
of the nation's foremost experts on chronic wasting disease. "Right now,
we don't have any firm results."
But Williams -the first to find evidence of the disease in the brains of
infected animals -and her colleagues in
Colorado have uncovered some clues:
In a report published last month in the science journal Nature, Williams
and Mike Miller, wildlife veterinarian for
the Colorado Division of Wildlife, concluded that the disease is spread
from animal to animal and that transmission directly
from mother to fawn or calf probably is not significant. The findings
also suggest the disease could spread among
congregating animals.
Miller and Williams placed nine pregnant does with the disease in pens
at the Division of Wildlife's Foothills
Research Unit in Fort Collins. They also turned out nine disease-free
fawns from the wild in the pens, with the goal of
finding out whether only the fawns born of the infected mothers would
contract the disease. All nine did, but so did eight of
the nine fawns from the wild.
In other studies, animals were taken from areas where the disease did
not exist and placed into pens where infected
animals had been. They did not have direct contact with infected animals
but still developed the disease.
"There's strong evidence it can be picked up from the environment,"
Williams said.
The studies are funded by the National Institutes of Health, the
National Science Foundation, the Department of
Defense, the U.S. Department of Agriculture and Wyoming’s and Colorado's
state wildlife agencies.
Chronic wasting disease research, on all fronts, is going on across the
nation and in Europe. Most in the U.S. is a
cooperative effort between federal and state agencies and universities.
The University of Wyoming, Colorado State
University, the Wyoming Game and Fish Department and Colorado's Division
of Wildlife often work together on chronic
wasting disease research.
The Department of Defense, which often is involved in medical research,
recently awarded $2 million to a collaborative CWD study involving the
University
of Wyoming, the Wyoming Game and Fish Department and the Colorado Division
of Wildlife. The study will attempt to develop sensitive prion-detection
techniques
and use them on samples from CWD-affected deer and elk in hopes of better
understanding how CWD is transmitted.
Colorado and Wyoming also are testing about 24 cattle at the Foothills
Research Unit and the Game and Fish Department's Sybille Wildlife
Research Unit
to determine whether cows can contract chronic wasting disease by
contact with
sick elk and deer. Cattle often share pastures and public land with deer
and elk.
Chronic wasting disease belongs to the same family of diseases as "mad
cow" (bovine spongiform encephalopathy) called transmissible spongiform
encephalopathies, or TSEs. A form of bovine spongiform encephalopathy
(BSE) has
caused a human disease called variant Creutzfeldt-Jakob disease, 'which
has killed
about 140 people primarily in England and Europe since the 1990s. The
victims
most likely became infected by eating beef contaminated with the BSE agent,
raising concerns in North America about the possibility of CWD
transmission to
humans.
Studies to date, however, have shown cattle appear to be resistant to CWD
by natural routes of exposure. But the studies, set to go for 10 years,
are not
complete. Research cattle fed a high dosage of brain material from
infected mule
deer and elk still are healthy. Cattle living in the same research
facilities in Sybille
and Fort Collins as infected deer and elk also still are healthy.
When a herd of captive deer and elk
is infected with chronic wasting
disease, the proportion of sick
animals is generally much higher
than it is in infected wild herds.
Evidence strongly suggests that
shipment of animals from one game
ranch to another has spread CWD
much faster than it spreads in the
wild. (Photo by Beth Williams)
Even when thirteen cattle were inoculated with the CWD agent directly into
their brains, where the disease begins, only five showed evidence of
transmission,
Williams said.
"Of course, that's an abnormal route of transmission, but it shows us what
CWD might look like if it occurred in cattle, and indicated that our
diagnostic tests
are adequate to pick it up."
Research indicates that CWD does not spread from deer to cattle or other
domestic livestock. However, deer that are fed
through the winter in a CWD area are much more likely to develop the
disease than deer wintering in native habitat.
(Photo by LuRay Parker)
Along with the states, the USDA is monitoring cattle in Wyoming and
Colorado and throughout the country for
BSE by examining cattle with neurologic disease. So far, no evidence of
BSE or CWD transmission has been found.
Colorado State University also examined about 250 culled cows from
northeast Colorado, where chronic wasting disease
has been established for decades and cattle often are free roaming along
with deer and elk. Nothing was found.
Several agencies, such as the Food and Drug Administration, are carrying
out studies on risks to human health. A
two-year, $500,000 FDA study with the Harvard Center for Risk Analysis
focuses on the risk of BSE transmission to
humans through FDA-regulated products. Another three-year, $2 million to
$3 million FDA study at Case Western Reserve
University with the Centers for Disease Control and Prevention uses
genetically engineered mice developed to study the
transmissibility of CWD. The mice carry either a human or deer gene for
normal prion protein and are exposed to tissue
from CWD-infected animals.
The National Institute of Allergy and Infectious Diseases awarded a
seven-year, $8.4 million contract to Colorado
State University. The university is investigating how CWD progresses
within deer and elk and how it could jump the
species barrier. Researchers already have mapped out how it progresses
through the brains of deer, and currently are
working on elk. Eventually, they will attempt to develop a vaccine to
protect deer and elk.
Researchers at NIAID' s Rocky Mountain Laboratories in Hamilton, Mont.,
are developing compounds that could
block the formation of prion proteins.
On the wildlife front, Colorado Division of Wildlife researchers are
studying the relationship between high
numbers of deer in an area and the occurrence of the disease. They are
using a "test-and-cull" tactic in Estes Park just
outside Rocky Mountain National Park, a town where the robust elk
population is known to snack on residents' yards and
share the road with cars.
Colorado's Miller said wildlife officials were looking for an urban area
where hunting is limited. They caught,
marked, and tested about 200 adult mule deer for CWD with a new live
animal test using tonsils. They then went back and
removed the positive deer.
They also are culling deer in areas where there are a high number of
cases to see if it halts the disease's spread;
studying whether other big game animals, such as bighorn sheep, can
contract the disease, whether deer movement is
connected with disease prevalence and experimenting with early detection
methods to diagnose CWD in healthy-looking
animals. Right now, examining brain and lymph node tissue, which
requires an animal to be killed, is the only approved
way to know whether an animal is infected.
Private companies, working with veterinary diagnostic laboratories
including the Wyoming State Veterinary
Laboratory at the University of Wyoming and state wildlife management
agencies, are working to hone and improve testing
methods. A new test, ELISA, has now been approved by the USDA. Results
of the test, which identifies prions in an
animal's lymph nodes, come back in about a day, instead of more than two
days, which is required with the old gold
standard - immunohistochemistry -which still is being used to confirm
positive cases. With ELISA, a hundred samples can be run at once instead of
a just a few. Wyoming and Colorado both are using the new method, and new
CWD diagnostic tests are being developed and will be available in coming
years.
Along with laboratory work, intensive monitoring across the nation
through hunter-killed and culled animals has helped researchers gain insight
into the disease. Results so far suggest CWD is relatively localized and not
widespread, said Williams.
"It's not surprising CWD was found in northeastern Utah, because
deer and elk migrate from areas in Colorado where CWD occurs," Williams
said. "But there are a few occurrences of CWD in distant areas that are
unexplained." CWD was found in deer on the White Sands Missile Range in
New Mexico in 2001.
Researchers can't figure out a link in some of these cases, if there is
one, because they have no way yet of tracking strain types.
But there's evidence commercial game farms, which are banned in
Wyoming and Montana but allowed in other states, could have contributed to
the disease's geographic spread, Williams said.
"We don't expect with fence-line contact over the short term that an
animal would contract the disease," she said. "But with long-term
interaction,
particularly when deer or elk can get through fences, the risk is
increased."
Officials and politicians have called for more money to develop
better laboratory techniques and a better understanding of chronic wasting
disease and how it spreads. But adequate funding for CWD research, which is
expensive, as it often requires large facilities to house large animals,
is limited.
The prion that causes chronic wasting
disease focuses on nerve tissue,
especially in the brain. Infected brain
tissue shows microscopic holes. One
way of identifying the disease is to
take a sample from the base of the
brain, treat it with a special stain,
and examine it under a microscope
for signs of spongy tissue and tinted
prions. by Beth Williams
The U.S. Geological Survey was appointed as a clearinghouse for
allocating and coordinating federal funds for research, but often the
financial
burden of CWD research falls on the states. Colorado's wildlife division
foots
90 percent of its bills on CWD research and surveillance, allocating $3.5
million this year, up from $2.9 million the year before. Wyoming spent
$238,927 of Game and Fish Department funds last year for CWD surveillance
and management. This year, the department received $240,557 from the U.S.
Department of Agriculture earmarked for surveillance and management.
SURVEILLANCE AND REGULATIONS - article by Michelle Zitek and Tom Reed
The Wyoming Game and Fish Department is going to be testing deer
statewide this year to determine if chronic
wasting disease has spread outside the current known boundaries.
Department employees will be working at selected meat processors and
check stations across the state the first five
days of deer seasons. In addition to collecting the customary bio-
logical data, employees will remove lymph nodes for
CWD tests.
"Expanding surveillance will allow us to better understand the
distribution of this disease," said Hank Edwards,
wildlife disease specialist with the department. "Past surveillance
efforts allowed us to document CWD in new hunt areas
and we hope expanded surveillance will allow us to identify the leading
edge of the disease."
When hunters arrive at check stations they will be asked if they would
like to participate in the CWD surveillance
program. If they do, trained employees will remove the animal's lymph
nodes. This will not affect the meat, but may affect
the hunter's ability to have their trophy mounted.
"Hunters who wish to have their animal mounted will need to make
arrangements with their taxidermist to retrieve
the head after it has been caped if they choose to submit it for
testing," said Edwards.
Employees will record detailed information about where the deer was
harvested and will apply barcode stickers to
the hunter's license and corresponding samples to make sure the hunter
information is matched to the correct animal.
Testing is voluntary, but as a service to those who take time to
participate, the department will post test results on
its Web site. Hunters will need their barcode numbers to obtain results,
and results will be posted as they become available.
Completing tests will take about twelve weeks. Hunters will be notified
by letter if their animal tests positive.
The department is working with other state wildlife agencies, and
will contact those agencies in the home state of any nonresident hunter
whose
animal tests positive.
Hunters who do not participate in the surveillance program may have
their animals tested at their own expense at the Wyoming State Veterinary
Laboratory in Laramie. Some vets around the state have been trained to take
samples and may be willing to work with hunters to obtain samples and ship
them to the appropriate place.
Deer and elk hunters headed to the field this fall should be aware that
a number of states have adopted new regulations pertaining to the
transportation of hunter-harvested deer and elk. These regulations are in
response to growing concerns about the spread of CWD, and are an attempt
to minimize the risk of spreading the disease into new areas.
The first objective in the management of CWD is to prevent its
spread. One theoretical mode of disease transmission is via infected
carcasses.
Since the suspected infective agent (prion) is concentrated in the
brain, spinal
cord, and lymph glands, the most common regulation is the prohibition of the
importation of whole carcasses harvested from CWD areas. Some states, like
Colorado, also have established regulations addressing the transport of deer
and elk out of CWD areas. Generally, states that have adopted carcass
transportation regulations do not allow the importation of any brain or
spinal
column tissue and allow transport of only the following:
• Meat that is cut and wrapped (either commercially or privately);
• Quarters or other portions of meat with no part of the spinal column
or head attached;
This fall, Game and Fish employees
will take lymph nodes from the necks
of dead deer to check for chronic
wasting disease. Research has shown
that prions tend to concentrate in
these tissues. (Photo by Chris
Madson)
• Meat that has been boned out;
• Hides with no heads attached;
• Clean (no meat or tissue attached) skull plates with antlers attached;
• Antlers with no meat or tissue attached;
• Upper canine teeth, also known as "buglers," "whistlers," or
"ivories":
• Finished taxidermy
California, Colorado, Illinois, Iowa, Manitoba, Michigan, Minnesota,
North Dakota, New Mexico, New York,
Oregon, Rhode Island, South Carolina, Utah, and Vermont have adopted
some form of carcass transportation regulations.
Since these regulations are continually evolving, we recommend that
hunters check the CWD regulations before
hunting- this should include the regs in their home states, the state in
which they will be hunting, and the sates through
which they will travel on their way home from the hunt. Most state
wildlife agencies provide regulation information on
their Web sites and may be accessed through the CWD Alliance Web site’s
CWD LINKS page,
www.cwdinfo.org/index.php/fuseaction/links.main.
Here’s an example of what some states are doing:
Colorado – As a precaution against the possible spread of chronic
wasting disease, only the following carcass parts
may be transported out of infected units in northeastern Colorado (units
7,8, 9, 19, 20, 38, 87, 88, 89, 90,91,92,93,94, 95,
96, 191,951) or brought into any part of Colorado from infected areas in
other state: 1) Meat that is cut and wrapped (either
commercially or privately); 2) quarters or other portions of meat with
no part of the spinal column or head attached; 3) meat
that has been boned out; 4) hides with no heads attached; 5) clean (no
meat or tissue attached) skull plates with antlers
attached; 6) antlers with no meat or tissue attached; 7) upper canine
teeth, also known as "buglers," "whistlers," or
"ivories": 8) finished taxidermied heads.
California- On April 4, 2002, the California Fish and Game Commission
adopted regulations restricting the
importation of hunter-harvested deer and elk into California to replace
the emergency regulations enacted earlier in 2002.
The new regulations went into effect June 5, 2002, and eliminated the
seventy-two-hour grace period provided in the
emergency regulation and do not allow the importation of any brain or
spinal column tissue. Other body parts allowed by
the proposed regulations include quarters and other portions of meat
with no spinal column or head attached, hides with no
heads attached, clean skull plates with antlers attached, antlers only,
finished taxidermied heads, and upper canine teeth.
Illinois- The Illinois Department of Natural Resources is allowing
hunters to bring deer and elk hunted out of state
back into Illinois so long as the carcasses are brought to a licensed
meat processor or licensed taxidermist within seventytwo
hours of entry into the state.
The rule amends an earlier prohibition on the transportation of hunter-
harvested deer and elk carcasses into
Illinois, except for deboned meat, antlers, antlers attached to skull
caps, hides, upper canine teeth, and finished taxidermy
mounts. Individuals who do not take their harvest to either a licensed
meat processor or licensed taxidermist still must
comply with this regulation.
The rule requires meat processors and taxidermists to dispose of
discarded animal materials either with a renderer
or in a landfill. Hunters are strongly advised to consult with their
state agencies on carcass transport before leaving for the
hunting area.
This cow elk is being held at the Wyoming Game and Fish Department's
Sybille Wildlife Research Center. She has been
infected with chronic wasting disease and is beginning to show the rough
coat often seen in the final stages of a CWD
infection. Investigators at Sybille are trying to find out how CWD is
transmitted from one animal to another. (Photo by
Chris Madson)
RISK TO HUMANS - article by Tom Reed
Federal health officials thought they were on to something last year.
Three Midwestern men, who were known to
have eaten wild game at a cabin in Wisconsin, all died from strange
neurological disorders. Perhaps, they thought, here was
a connection between Creutzefeldt-Jakob disease (CJD) and wild game
meat. CJD is a rare fatal brain disorder with about
one case per million people diagnosed each year. There are essentially
three ways for a human to get CJD: sporadically,
which means there is no apparent cause; genetically; and it can be
transmitted through infection. The agent that carries the
disease is thought to be a protein, a pathogen called a prion, which is
a nickname for "proteinaceous infectious particle."
Investigations commenced. Relatives and friends were interviewed. Brain
tissue from the victims was analyzed.
In the end, the trail between game meat consumption and CJD went cold.
It turns out that only one of the victims died from
CJD, and he was not a frequent participant in the game feasts at the
cabin, according to Dr. Ermias Belay, M.D. "That
cluster didn't pan out," said Belay.
So far, scientists have not been able to find a link between CJD and the
consumption of game meat from an animal
infected with chronic wasting disease. The fear is that since CWD is a
brain disorder in deer and elk, the consumption of
meat from infected deer and elk could lead to CJD in humans. So far,
however, scientists haven't found that to be the case.
"There's no direct evidence for CWD transmission to humans," said Belay,
a medical epidemiologist with the
federal Centers for Disease Control in Atlanta. "But, there's not a lot
of studies looking for such evidence."
CJD was first identified in humans by Dr. Hans Creutzfeldt and Alfons
Jakob in the 1920s. It's not a pretty disease
by any means. Victims display ever-increasing debility, including
progressive dementia and uncontrollable muscular action.
There is no known cure.
So if there is no evidence that CWD jumps across species boundaries
(cervid to human) why all the fuss? The
answer lies overseas. In the mid-1990s, scientists in the United Kingdom
identified a possible link between the so-called
mad cow disease and a variant form of CJD. For the first time,
scientists speculated that humans could get a form of CJD
from eating infected animal products. Mad Cow Disease, also known as
bovine spongiform encephalopathy (BSE), was
initially discovered in 1986 in the UK and was thought to be transmitted
to the cattle through their feed. This cattle feed
included, in part, groundup portions of BSE-infected cattle or sheep
that had scrapie (another prion- based brain disorder).
Further compounding the problem was the practice of using all the parts
of the slaughtered animals such as brains, bones,
spinal columns, and lymph nodes in such delicacies as sausages, before
regulations brought such things to a halt. According
to the Creutzfeld- Jakob Disease Foundation, scientists in the UK-
without direct evidence of a link between the variant
form of CJD and BSE- theorized that the most likely way to get the new
form of the disease was by eating these animal
byproducts. Panic swept across the British Isles, and farm animals were
slaughtered by the thousands and burned in huge
piles. Television news stations around the world carried images of
smoldering carcasses being burned and buried.
There is no evidence that chronic wasting disease can infect humans.
Still, no one wants to shoot a sick deer if he can avoid
it. So the first precaution a hunter should take is simple- don't shoot
deer that seem emaciated or are acting strangely.
(Photo by Tim Christie)
But the untold story behind the mad cow panic is the fact that only 136
people have been diagnosed with that
variant CJD, with an exposure factor in the millions in the UK alone.
It's likely that about a billion people (that's three times
the population of the United States) have been exposed to BSE since it
was identified and only 136 have died. What's more,
those victims all seem to have a similar genetic makeup.
"The outbreak is not over yet, they are still counting, but it's clearly
not exploding," said Belay.
For perspective, consider this: In the decade since UK scientists
theorized that there was a link between BSE and the variant
CJD, only 136 people have been identified with the disease. They seem to
have a similar genetic makeup, and they quite
probably ate meat products that contained offal like brains and bone
meal. More people died on Wyoming's highways last
year alone-l 75- than have died from the millions exposed to BSE in its
history. Drunks behind the wheel on our nation's
highways killed more than 100 times as many people last year
alone-17,000. In 1997, more than 32,000 people were killed
by firearms, and if you just want to focus on diseases, consider that
cancer in the United States kills the equivalent of the
entire population of the state of Wyoming- more than 550,000 people-
every year.
"You look at those factors, things like road deaths and gunshot deaths,
hunters accept those risks all the time," said
Dr. Patrick Bosque, a neurologist with the Denver Health Hospital and a
faculty member of the University of Colorado,
"They seem to accept those risks as reasonable, I guess."
Bosque has been studying prions in laboratory settings for a decade and
studied under Stan Prusiner, the
University of California-San Francisco scientist who won the Nobel Prize
for his work with prions.
"People worry more about the bizarre and unusual than they do about
familiar risks," said Bosque. "It's uniformly
fatal and unusual, and that's why people are worried about it because so
much is unknown about it. My take on it is if I
were eating venison and knew the animal had been tested-and I think it's
reasonable to test every animal-I would eat it.
From a human health perspective, it is just common sense to avoid
eating diseased animals, said the CDC's Belay.
"If the animal is positive, it's probably not a good idea to eat an
animal that is sick with any disease at all," said
Belay. "It's a common-sense precaution to not eat it, particularly if
you don't know whether or not it has CWD."
Several studies are looking at death records and hunter information to
see if there's any link between CWD and
unusual neurological deaths. So far, no link has been identified.
"The data to this point that we've looked at in Colorado says that it's
either not occurring, or if it does, it does so
rarely that we are unable to pick it up," said John Pape, epidemiologist
with the Colorado Department of Health and
Environment. "But the data right now is not strong enough to exclude
that possibility (that CWD can be transmitted to
humans). That's why we recommend hunters take precautions."
In the lab, Bosque and his assistants take special precautions when
dissecting lab specimens, including wearing
gloves and being shielded from any material such as blood and offal. He
recommended similar precautions for hunters
afield taking game animals. "I'd recommend wearing gloves and an eye
shield of some sort," said Bosque.
The Wyoming Game and Fish Department recommends several precautions for
hunters: Do not harvest or eat wild
animals that appear sick; Wear rubber or latex gloves as a routine
precaution when field dressing; Minimize handling of
brain and spinal tissues and wash hands, knives, and saws afterward;
Meat should be boned out when the animal is
butchered; Do not eat the brain, spinal cord, eyes, spleen and lymph
nodes of harvested animals.
In the end, scientists are not ruling out that eating CWD-tainted elk or
deer could lead to a prion-based brain
disease like CJD, but so far, there is no proof or any scientific
evidence that is the case. Regardless, based on the extremely
long odds demonstrated with BSE and variant CJD in Europe, the chances
of someone getting CJD from eating venison
from a CWD-infected animal are very, very slim. But, more study is
needed and in the meantime, hunters should take the
necessary steps.
"It's new; it's a horrible disease that is poorly understood even among
scientists and is clearly not understood
among the public," said Pape.
@ Wyoming Game & Fish Dept. http://gf.state.wy.us/downloads/pdf/cwdarticle.pdf TSS ################# BSE-L-subscribe-request@uni-karlsruhe.de #################
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