Deer disease a serious concern for wildlife managers
November 16, 2013 8:02 PM
Jake Dingel/Pennsylvania Game Commission
Like humans, deer get sick and deer disease is a serious concern.
By Ben Moyer / Special to the Post-Gazette
What sports fan has not used the phrase "He runs like a deer?" It's praise for an athlete's agile speed but also a nod to that four-legged sprinter. We view deer as fast and fit.
But like humans, deer get sick and deer disease is a serious concern for wildlife managers and hunters today.
That concern grew with the Game Commission's discovery in the spring of chronic wasting disease in three deer killed by hunters in Blair and Bedford counties. The discovery followed by mere months the confirmation of a captive CWD-positive whitetail on a deer farm near Gettysburg in Adams County.
CWD is a transmissible, always-fatal disease of deer, elk and moose. The disease was first discovered among captive mule deer in Colorado in the 1960s but has spread to wild or captive deer in 20 states and two Canadian provinces. Eastern states with documented infections include New York, Maryland, Virginia, West Virginia and Pennsylvania.
No deer carry genetic immunity to CWD, deer cannot develop immunity and there is no vaccine or cure. CWD cannot even be diagnosed with certainty until after death, when the brain of the affected animal is tested.
CWD's arrival in Pennsylvania followed closely behind a recent surge of epizootic hemorrhagic disease, which spread rapidly among deer herds across southwestern counties at least three times since 2002. While CWD is always fatal, some deer may recover from EHD, although there is little evidence of recovery of infected deer in Western Pennsylvania. Following an outbreak, local populations can bounce back within two to three years, according to biologists.
PG graphic: Deer disease management (Click image for larger version)
Both ailments can cause victims to display similar symptoms (drooling, weakness, loss of fear of people, weight loss) and some hunters confuse the two or assume they're the same. But CWD and EHD are different diseases, spread in fundamentally different ways with different implications for hunters.
EHD is spread by biting midges of the genus Culicoides. Midges transmit EHD by introducing a virus into healthy hosts as they feed on deer blood. The disease peaks during drought conditions in late summer. Mud exposed as streams and lakes dry offers habitat for the Culicoides midge, resulting in wider spread of EHD. Infected animals hemorrhage fluids from organs, dying within days unless they carry immunity.
The incidence of EHD results from random climatic events, so there is not much hunters and managers can do to contain it. That's not the case with CWD, which spreads directly from deer to deer by contact with saliva, feces or urine. It also spreads indirectly when deer ingest soils, and possibly plant matter, that harbor "prions" -- malformed proteins that attack brain cells, forming sponge-like holes. The infectious prions concentrate in the brain, eyes and spinal column.
"We are no longer in a mode where we are trying to keep CWD out; it's already here," said Cal DuBrock, director of the Game Commission's Bureau of Wildlife Management. "Our aim now is containment, management and monitoring."
The Game Commission has set up Disease Management Areas with special rules affecting deer hunters in the two parts of the state where CWD is currently known to exist.
DMA 1 covers 600 square miles in Adams and York counties. DMA 2 includes 900 square miles across parts of Bedford, Blair, Cambria and Huntingdon counties.
These rules are similar to those in force for several years regarding deer shot in other states with known CWD infected zones.
Hunters who kill a deer within a DMA may not remove any high-risk part of the animal from the DMA. High-risk parts include the head (including brain, tonsils, eyes and lymph nodes), spinal cord, backbone and skull plate if any visible brain tissue is present. Hunters may transport antlers attached to the skull plate outside DMAs if all brain tissue has been cleaned away. Meat can be moved from within DMAs if no high-risk parts are present.
Hunters who process their own deer shot within DMAs are asked to dispose of high-risk parts in dumpsters provided at specified locations. Those parts will be transported to approved landfills.
"We're trying to control movement of parts that are most likely to expose a healthy deer population to infectious prions," DuBrock said.
The feeding of deer within DMAs is also prohibited, and hunters may not use urine-based lures and attractants while hunting deer inside DMAs.
"We want to minimize activities that cause deer to congregate more than they normally do," DuBrock said. "Deer are social animals but human activities such as baiting and feeding cause abnormally high concentrations. If any of those deer are unhealthy, you can have an outbreak."
DuBrock said he knows the ban on urine-based attractants will be controversial, but he appealed to hunters' sense of responsibility to the resource.
"We hope hunters will help us," DuBrock said. "It's clear that prions are found in urine, which is collected from captive populations of unknown status to make lures. The prions are viable for long periods in the environment and they bind to soil, increasing the potential for exposure."
There is no evidence that CWD can be transmitted to humans, but hunters are cautioned to use common sense and avoid deer that are obviously sick.
"If anyone becomes aware of a deer out there that's sick, please call the regional Game Commission office [southwest region 724-238-9523] and report it to us," DuBrock advised.
Although managing CWD presents a serious concern, DuBrock asks hunters to view the situation in context.
"Continue to enjoy deer hunting as you have in the past," he said. "We are examining thousands of deer every season and there is very little evidence of disease among the broader population. For that we are grateful. Pennsylvania hunters can take a deer and feed it to their families with great confidence."
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