Tom Morang
04-06-2002, 06:50 AM
Deadly disease stumps wildlife vets
By Phil Berardelli
UPI Deputy Science and Technology Editor
From the Science & Technology Desk
Published 4/6/2002 0:00 AM
An insidious disease infecting deer and elk populations across a widening expanse of western America has forced agricultural and wildlife officials to kill more than 10,000 animals because they still do not know how it is transmitted.
Chronic wasting disease has become such a problem some officials are calling it a wildlife emergency.
"If we can't manage the spread of infection, it could eliminate the entire deer and elk populations within 100 years," said Dr. Mike Miller, a veterinarian for the Colorado Division of Wildlife in Fort Collins.
CWD belongs to a family of diseases called transmissible spongiform encephalopathies or TSEs. A related mouthful of a name, bovine spongiform encephalopathy or BSE also is known as the dreaded "mad cow" disease.
For at least 35 years, CWD slowly has been killing antlered fauna across a portion of Colorado and Wyoming. Recently, the disease has appeared in Kansas, Nebraska, Wisconsin and even in southern Canada. The spread of infection has raised alarms among state game officials, hunters and others who manage the herds or harvest the animals for human consumption.
Miller is especially worried because the wild herds have not yet shown any evidence of CWD resistance. That is critical, Miller told United Press International, because with most diseases, some members of an infected species eventually develop immunity to the invading organism. It is what allows a population to survive.
He also said CWD is very difficult to spot within herds because of its long incubation period, which may be three years or more. Animals can show no symptoms well after they have been infected.
Most wildlife managers believe the rise of commercial game farms -- ranches that raise elk and other formerly wild animals to serve the growing demand for exotic meats -- have served as incubators for CWD's spread. As a result, several western states have slapped restrictions on game farms and on interstate transportation of deer and elk.
Miller explained that diseases infecting wild mammals tend to progress slowly because the species live in isolated populations and migrate over limited distances. Because game farms collect deer and other animals from widespread areas, however, infected animals from one area can contaminate captive herds all over North America.
CWD was first detected in a captive research herd in Fort Collins, although its ultimate origin remains unknown.
The mystery of how CWD spreads especially concerns wildlife scientists.
"We know it's not a food-borne disease like BSE," said Elizabeth Williams, professor of Veterinary Science at the University of Wyoming. "Most likely, the agent gets out in the feces or saliva. But there may be other possibilities."
Williams told UPI current theories about CWD suggest it emerged as a variation of scrapie, the most common TSE disease that has infected sheep in Europe and North America for centuries. Or, perhaps it is a new strain of BSE -- although so far there is no evidence that connects it to cattle.
Williams said it is especially troubling that CWD does not seem to require direct contact among animals to spread, a fact that deepens its mystery and increases worry among epidemiologists -- scientists who study infectious diseases.
"In my mind, it's still a great puzzle," said Dr. Byron Caughey, a specialist in TSEs at Rocky Mountain Laboratories in Hamilton, Mont.
Even though CWD only infects deer and elk, Caughey and other researchers are keeping a close watch on the disease. They are concerned because of how easily it can be transmitted in the wild.
"It is important to remember that TSEs are not often contagious," Caughey told UPI. "You usually have to work hard to spread them."
Caughey explained the notorious mad cow disease outbreak in England occurred under extremely unusual circumstances. The beef industry there began grinding up excess cattle parts to include in the feed of live animals. That allowed the BSE organisms to be consumed, greatly increasing the chances of infection.
"When they banned the practice, they reduced the incidence of the disease," he said.
Caughey noted even the deadly Creutzfeldt-Jakob disease, the one TSE that can infect humans, is very difficult to transmit. CWD, however, already has "jumped species" and spread in the wild, moving from deer to elk or vice versa. That is why "it's worrisome," he said.
Worry is why so many animals, wild and captive, have been killed so far in an effort to eradicate CWD. Tim Feldner, manager of the commercial wildlife permitting program for the Montana Department of Fish, Wildlife and Parks, said the infection rate among the captive herds has been as high as 50 percent.
"Population densities seem to make a big difference in terms of the incidence of the disease," he said. That is why most of the CWD-related killing has taken place on the game farms.
Although a 50 percent infection rate is high, Feldner told UPI, other wildlife diseases can be far more deadly. Another long-named malady, epizootic hemorrhagic disease, or EHD, has been infecting deer for many years. It is an insect-borne virus that can quickly wipe out a significant portion of a herd, but then disappear for years before causing problems again.
CWD is not so devastating, but it can be just as scary in its own way, Feldner said.
"It's a sneaky little disease that may be there all the time," he said. "And it will constantly take its toll."
Miller's agency, meanwhile, is in the second year of a three-year experiment to try to interrupt CWD's spread among Colorado's wild deer population.
"Other research and our own models suggested that reducing the herd density might slow the spread of the disease," he said.
According to Miller, a herd of about 2,200 mule deer has been targeted for a 50 percent reduction. The herd is dispersed amid a 1,250-square-mile game management unit in northern Colorado. It was selected because of a higher-than-normal CWD infection rate, he said.
The culling is being accomplished through increased hunting licenses. The current herd population already is maintained by annual hunting.
Wildlife officials also recently killed 300 deer near Craig, Colo., to see if they were infected after two deer found on an elk ranch tested positive for the disease.
At this point, Miller said, it is questionable whether the culling strategy will work. "Nobody's ever tried to manage a disease like this in the wild before," he said.
By Phil Berardelli
UPI Deputy Science and Technology Editor
From the Science & Technology Desk
Published 4/6/2002 0:00 AM
An insidious disease infecting deer and elk populations across a widening expanse of western America has forced agricultural and wildlife officials to kill more than 10,000 animals because they still do not know how it is transmitted.
Chronic wasting disease has become such a problem some officials are calling it a wildlife emergency.
"If we can't manage the spread of infection, it could eliminate the entire deer and elk populations within 100 years," said Dr. Mike Miller, a veterinarian for the Colorado Division of Wildlife in Fort Collins.
CWD belongs to a family of diseases called transmissible spongiform encephalopathies or TSEs. A related mouthful of a name, bovine spongiform encephalopathy or BSE also is known as the dreaded "mad cow" disease.
For at least 35 years, CWD slowly has been killing antlered fauna across a portion of Colorado and Wyoming. Recently, the disease has appeared in Kansas, Nebraska, Wisconsin and even in southern Canada. The spread of infection has raised alarms among state game officials, hunters and others who manage the herds or harvest the animals for human consumption.
Miller is especially worried because the wild herds have not yet shown any evidence of CWD resistance. That is critical, Miller told United Press International, because with most diseases, some members of an infected species eventually develop immunity to the invading organism. It is what allows a population to survive.
He also said CWD is very difficult to spot within herds because of its long incubation period, which may be three years or more. Animals can show no symptoms well after they have been infected.
Most wildlife managers believe the rise of commercial game farms -- ranches that raise elk and other formerly wild animals to serve the growing demand for exotic meats -- have served as incubators for CWD's spread. As a result, several western states have slapped restrictions on game farms and on interstate transportation of deer and elk.
Miller explained that diseases infecting wild mammals tend to progress slowly because the species live in isolated populations and migrate over limited distances. Because game farms collect deer and other animals from widespread areas, however, infected animals from one area can contaminate captive herds all over North America.
CWD was first detected in a captive research herd in Fort Collins, although its ultimate origin remains unknown.
The mystery of how CWD spreads especially concerns wildlife scientists.
"We know it's not a food-borne disease like BSE," said Elizabeth Williams, professor of Veterinary Science at the University of Wyoming. "Most likely, the agent gets out in the feces or saliva. But there may be other possibilities."
Williams told UPI current theories about CWD suggest it emerged as a variation of scrapie, the most common TSE disease that has infected sheep in Europe and North America for centuries. Or, perhaps it is a new strain of BSE -- although so far there is no evidence that connects it to cattle.
Williams said it is especially troubling that CWD does not seem to require direct contact among animals to spread, a fact that deepens its mystery and increases worry among epidemiologists -- scientists who study infectious diseases.
"In my mind, it's still a great puzzle," said Dr. Byron Caughey, a specialist in TSEs at Rocky Mountain Laboratories in Hamilton, Mont.
Even though CWD only infects deer and elk, Caughey and other researchers are keeping a close watch on the disease. They are concerned because of how easily it can be transmitted in the wild.
"It is important to remember that TSEs are not often contagious," Caughey told UPI. "You usually have to work hard to spread them."
Caughey explained the notorious mad cow disease outbreak in England occurred under extremely unusual circumstances. The beef industry there began grinding up excess cattle parts to include in the feed of live animals. That allowed the BSE organisms to be consumed, greatly increasing the chances of infection.
"When they banned the practice, they reduced the incidence of the disease," he said.
Caughey noted even the deadly Creutzfeldt-Jakob disease, the one TSE that can infect humans, is very difficult to transmit. CWD, however, already has "jumped species" and spread in the wild, moving from deer to elk or vice versa. That is why "it's worrisome," he said.
Worry is why so many animals, wild and captive, have been killed so far in an effort to eradicate CWD. Tim Feldner, manager of the commercial wildlife permitting program for the Montana Department of Fish, Wildlife and Parks, said the infection rate among the captive herds has been as high as 50 percent.
"Population densities seem to make a big difference in terms of the incidence of the disease," he said. That is why most of the CWD-related killing has taken place on the game farms.
Although a 50 percent infection rate is high, Feldner told UPI, other wildlife diseases can be far more deadly. Another long-named malady, epizootic hemorrhagic disease, or EHD, has been infecting deer for many years. It is an insect-borne virus that can quickly wipe out a significant portion of a herd, but then disappear for years before causing problems again.
CWD is not so devastating, but it can be just as scary in its own way, Feldner said.
"It's a sneaky little disease that may be there all the time," he said. "And it will constantly take its toll."
Miller's agency, meanwhile, is in the second year of a three-year experiment to try to interrupt CWD's spread among Colorado's wild deer population.
"Other research and our own models suggested that reducing the herd density might slow the spread of the disease," he said.
According to Miller, a herd of about 2,200 mule deer has been targeted for a 50 percent reduction. The herd is dispersed amid a 1,250-square-mile game management unit in northern Colorado. It was selected because of a higher-than-normal CWD infection rate, he said.
The culling is being accomplished through increased hunting licenses. The current herd population already is maintained by annual hunting.
Wildlife officials also recently killed 300 deer near Craig, Colo., to see if they were infected after two deer found on an elk ranch tested positive for the disease.
At this point, Miller said, it is questionable whether the culling strategy will work. "Nobody's ever tried to manage a disease like this in the wild before," he said.