Article published October 11, 2009
Ridding fatal disease in deer no small feat
Deer eat bad dirt. Deer get sick. Deer die.
That little scenario is much too simplified, but it covers the salient points about new research that confirms suspicions among wildlife veterinarians, who have suspected that the environment plays a significant factor in the transmission of chronic wasting disease — CWD — among deer, elk, and moose in the West and Midwest.
CWD first was identified in mule deer in Colorado in 1967; it is found in 14 states and two Canadian provinces. Michigan confirmed a single case in a captive white-tailed doe a year ago.
The disease has not been detected in Ohio, but it has caused big concerns and cost a lot of money for surveillance and testing where it has arisen. It also has cost states lost license revenue among hunters reluctant to pursue deer where CWD is prevalent.
Now researchers have found that CWD, a brain infection, is spread via feces of infected animals — often long before they show symptoms of the disease such as emaciation, drooling, and staggering.
CWD is always fatal to deer and has no cure. But it has not been shown to be transmitted to humans, though handling or consuming CWD-infected deer is not recommended.
A team led by Stanley B. Prusiner, director of the Institute for Neurodegenerative Diseases at the University of California-San Francisco, announced the findings recently in a study in the journal Nature. Prusiner is the 1997 Nobel Prize winner in medicine. The team also included researchers with the Colorado Division of Wildlife’s Wildlife Research Center.
The infectious agent in CWD is a form of protein called a prion. The researchers found that deer shed prions from tissue in their intestinal linings for up to a year before they develop the disease. The prions are passed in deer feces, or pellets, and become incorporated into the soil. They defy even radiation, so there is no apparent way to eliminate CWD once it is established in an environment.
In turn, deer inadvertently can ingest some infected soil or even pellets during daily grazing; thus CWD can be spread from animal to animal in a herd. Given that deer produce about two pounds of pellets a day, more and more soil becomes contaminated as infected wild deer move about or infected captive animals are trucked between states.
Up to 90 percent of animals in a captive herd can be infected, and up to a third of animals in the wild where CWD is known can be infected.
Which is why Michigan wildlife and agricultural authorities, for example, have been so aggressive and far-ranging in their CWD control plan.
They have culled the entire herd on the game farm in Kent County where the CWD-infected doe was found in the summer of 2008, and they also culled, with the owner’s permission, the herd from which the infected doe was purchased.
“This makes it essentially ironclad,” said Dan O’Brien, a Michigan Department of Natural Resources veterinarian, about the study findings. He added that researchers had suspected CWD transmission via feces, along with saliva and urine.
That deer in Prusiner’s study were shown to be spreading the infectious agent long before they showed symptoms of CWD is “pretty typical of a lot of infectious diseases,” the MDNR veterinarian said. And it makes plans to control CWD that much more challenging.
Looking “just among animals that look sick is not going to take care of the problem,” O’Brien said. Which is why the two captive herds were “depopulated,” while nine Kent County townships remain are under mandatory deer carcass-check rules, and why baiting deer or recreational feeding of deer is banned in the entire lower peninsula.
While surveillance and testing will continue, O’Brien said, only one case of CWD has showed up, “and we hope it stays that way.”
Mike Tonkovich, deer biologist with the Ohio Division of Wildlife, said while CWD has not been detected here, wildlife and agriculture authorities are not letting down their guard.
A surveillance and testing network stays in place and is up and running.
Tonkovich noted that “until a connection is made between CWD and human health, it’s probably not going to hit home. It’s flying under the radar of most hunters.”
Hunters, however, still can be a valuable aid in CWD surveillance as eyes and ears in the field.
“We definitely want to know about strange deer behavior,” said Tonkovich.
Though detecting already sick deer in the wild is too late in one sense, it comes down to a case of better late than never.
That at least would tip off wildlife authorities to the presence of a problem that otherwise cannot be detected early on.
Contact Steve Pollick at:spollick@theblade.comor 419-724-6068.
Permanent Link
|
|
 |
|
Search
advertisement
