The rate of chronic wasting disease (CWD) is on the rise among deer in Iowa County, Wisconsin and elsewhere across the state. CWD is a fatal, transmissible spongiform encephalopathy (TSE) similar to what is commonly known as mad cow disease that is caused by twisted proteins, or prions. For hunters, writes outdoors reporter Patrick Durkin, this means the disease might be affecting the herd now. For anyone who eats venison, this means greater chances that the disease could conceivably make the species jump and infect humans
, according to Dave Clausen, a veterinarian whose term on Wisconsin's Natural Resources Board expired in May.
About one out of every three male deer aged 2.5 years and older carries CWD in north-central Iowa County, as does one out of every six yearling male deer (1.5 years old), according to the Wisconsin State Journal, and the rates are climbing at about ten percent a year. As several experts told Durkin, the increasing rates are "unprecedented," "frightening," and "disturbing."
Over 633,000 hunters purchased licenses to hunt white-tailed deer in Wisconsin in 2012, according to the Department of Natural Resources (DNR). The primary deer hunting season (for guns) runs for nine days in late November. An exact number of Wisconsinites who eat hunted venison is not known, although media reports indicate it is large. But testing of these deer for CWD is on the decline, even as infection rates rise. In 2002, over 40,000 deer were tested in Wisconsin, and .51 percent tested positive. In 2012, 6,611 deer were tested, and 5.13 percent tested positive.
As then-Natural Resources Board member Clausen wrote in a white paper on CWD and human health in 2012, the "ever-increasing number of CWD infected deer on the landscape ... and the accompanying exponential increase of environmental contamination with CWD prion will result in increased inter-species, including human, exposure to the CWD prion .... Under our current management strategy[,] human exposure is and will increase."
Less Testing, More People Eating Infected Venison
One of the reasons why it is possible for CWD to make the species jump to humans is because of insufficient warnings to hunters by the DNR, Clausen says. The DNR website says there is "no strong evidence" that CWD can be passed to humans, but warns hunters to "minimize contact with the brain, spinal cord, spleen and lymph nodes" when processing deer.
But in 2010, the World Health Organization (WHO) changed its definition of infective tissue to include skeletal muscles from CWD-infected deer and elk. And a 2012 Centers for Disease Control and Prevention (CDC) study notes, "CWD prions are present nearly ubiquitously throughout diseased hosts, including in muscle, fat, various glands and organs, antler velvet, and peripheral and CNS [central nervous system] tissue." It concludes that the potential for human exposure to CWD from handling or eating material from infected deer "is substantial and increases with increased disease prevalence." Both the WHO and the CDC recommend that people avoid eating meat from CWD-infected deer or elk.
Unlike the WHO and CDC, Clausen said the Wisconsin Department of Health and Safety (DHS) will not publicly recommend against eating infected venison until there is hard evidence that someone has gotten Creutzfeldt-Jakob Disease (CJD, the human TSE) from eating infected venison. But he believes that the government should be operating on the precautionary principle -- that "if something is plausible, that we should be erring on the side of caution unless we have absolute hard evidence that it's not possible."
But, Clausen adds, the "precautionary principle is bad for business." If people become so concerned about contracting CWD that they stop hunting, it means a potential decrease in DNR revenue; and the federal government has stopped funding CWD testing and research in the last year or two. UW-Madison Professor Michael Samuel has seen federal research funds for studying "disturbing" new trends in CWD dry up. "There's little interest in CWD these days, Wisconsin and nationwide," he told Durkin.
With testing on the decline, the DNR "has tracked hundreds of cases" in which people have eaten infected venison and "knows that there are many more," according to the Wisconsin Center for Investigative Journalism. As the rates of the disease rise -- as the CDC notes -- "the potential for human exposure to CWD by handling and consumption of infectious cervid material ... increases."
CMD founder John Stauber says, "Every dead deer in the state should be tested, and no deer should be butchered, processed or eaten unless it has been tested free of the disease. The current situation is contaminating processing plants with infectious prions."