October 18, 2002
CWD Topic at UW-RF Forum on Food Safety
Wisconsin deer hunters will be allowed to harvest many more deer this season than in the past, and if they take the recommended precautions against Chronic Wasting Disease, a fatal disease of the nervous system that appears in deer and elk, they will be able to safely consume the venison. This was the consensus of experts in the field who gathered to exchange information at a daylong forum on topics relevant to food safety, Thursday, Oct. 17, at UW-River Falls.
The forum, "Emerging Issues in Food Safety," was sponsored by the animal and food science department of the College of Agriculture, Food and Environmental Sciences at UW-RF and the Cooperative Extension Service of the University of Wisconsin System. It was attended by scientists and technical people, students and the general public.
UW-RF food science Professor Purnendu Vasavada was coordinator for the forum. Vasavada also serves as food safety and microbiology specialist for UW-Cooperative Extension.
Eradication and intensive harvest zones have been defined in the Mount Horeb area near Madison where CWD was first detected, according to veterinarian Shelby Molina from the Wisconsin Department of Agriculture, Trade and Consumer Protection. In these zones, she said, the goal is to completely destroy the deer herd. This will be accomplished by extending the hunting season and limits for hunters.
The meat of the deer from these two zones will not be consumed. Hunters will take their deer to collection stations, where it will be tested for CWD. Carcasses that test negative will be deposited in a landfill, and those that test positive will be burned.
In other areas of the state, hunters will be allowed to purchase additional carcass tags and additional hunts will be arranged to bring the deer population down to a more manageable level.
Molina outlined precautions hunters must take for field dressing and processing a deer. The recommendations include: wearing latex or rubber gloves; removing all internal organs; minimizing contact with the brain, spinal cord, spleen and lymph nodes; avoiding the use of household utensils; boning out the venison; and cleaning residue from knives and equipment, then disinfecting them with a 50/50 solution of household bleach and water.
It is important to clearly label where the deer was harvested, then take it to be tested and wait to see that the meat tests negative for CWD before consuming.
Because hunters will be able to harvest more deer than they can use, Molina suggested they give the extra meat to friends or family members, or donate the deer to a participating food pantry.
Scientists believe CWD is caused by a protein called a prion. Prions concentrate near nerve tissue in the brain, spinal cord, eyes, lymph nodes and spleen. Because of this, scientists recommend that these parts of the animal be removed and not eaten. Prions haven't been found in muscle tissue, which is the meat, and this is what most people consume. Thus, the meat of venison is considered safe to eat if it has tested negative for CWD.
Molina concluded with a reminder that no evidence linking CWD to human illness has ever been substantiated, but it is impossible to prove that CWD will absolutely never cause human illness.
In a discussion on the problems and prospects surrounding CWD and prion diseases, epidemiology Professor Will Hueston from the University of Minnesota said that to effectively deal with CWD it will be necessary to implement a program of vigilance and stick to it. "We need a scientifically-sound plan, and coordination between state and federal agencies," said Hueston, who is the director of the Center for Animal Health and Food Safety at the University.
"If we were to just ban deer hunting, we would have more incidence of Lyme's Disease and collisions on the road between cars and deer."
Hueston said a good plan would consider diagnosis of CWD, control and eradication, disposal, and transmission of the disease to other species. Of diagnosis, he said if an animal doesn't test positive, that doesn't mean the animal hasn't been exposed to CWD. It only says the animal doesn't have the disease yet. There appears to be a 16-to-18-month delay between exposure and the disease.
Control and eradication depend on testing for the disease, then eradicating the herd if it is infected. "In Colorado and Wyoming, where the disease originated, it was slow to spread because there are low animal densities in those states. Wisconsin has one of the densest deer populations in the country, with more than 100 deer per square mile, so the disease can spread quickly here," he said.
Because the immune system doesn't seem to play much of a role in CWD, it isnt possible to immunize for the disease. It spreads quickly through a herd by direct contact, probably in an exchange of saliva when the deer touch noses.
Disposal of the diseased carcasses must be handled in a way that presents the least risk to other animals, such as burning. To date, Hueston said, CWD has spread only between deer and elk. Cattle grazing on the same land or held in the same pen have not become infected.
"However, if we inject infected deer brain into cattle, we can infect the cattle, so we can't say CWD will never spread to cattle," he said.
Minnesota will be stepping up its surveillance for Chronic Wasting Disease, since the first incidence of the disease in the state has recently been discovered in an elk on a game farm near Brainerd.
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