Chronic wasting disease1 (CWD) is a form of bovine spongiform encephalopathy (BSE), a lethal neurological disease. CWD is very similar to mad cow disease, another form of BSE, but whereas mad cow affects cattle, CWD affects deer, elk and moose. The human disease variant of mad cow is known as Creutzfeldt-Jakob.
BSE is caused by toxic and infectious proteins known as prions, not bacteria or viruses, as one might expect. Infected animals typically die within three years. As previously explained in Scientific American:2
"Prions are misshapen yet durable versions of proteins normally present in nerve cells that cause like proteins to misfold and clump together, starting a chain reaction that eventually consumes entire brain regions … [S]cientists have learned that such a process may be at work not only in mad cow and other exotic diseases but also in major neurodegenerative disorders...."
Indeed, in the past two decades, researchers have discovered a compelling link between a particular kind of protein known as TDP-43 — which behaves just like the toxic prions causing BSE — and human neurodegenerative diseases such as Alzheimer's, Parkinson's and Lou Gehrig's disease.3
According to research4 published in 2011, TDP-43 pathology is detected in 25 to 50 percent of Alzheimer's patients, particularly in those with hippocampal sclerosis, characterized by selective loss of neurons in the hippocampus, which is associated with memory loss. Other research shows Alzheimer's patients with TDP-43 are 10 times more likely to have been cognitively impaired at death than those without it.5,6
CWD Is on the Rise
According to recent reports, CWD is now found in 16 percent of male animals tested in Colorado. One particularly hard-hit herd of deer in Boulder, Colorado, was found to have an infection rate of 40 percent. As noted by The Denver Post,7 Colorado Parks and Wildlife leaders recently announced that combating CWD is a top priority. To that end, a special task force has been launched to develop strategies aimed at tracking the disease.
A key component is to require hunters to test their kills for presence of CWD, and to reduce prevalence by encouraging hunters to hunt bucks in herds known to have high infection rates. (It should be noted that infected animals should NOT be eaten, due to the potential risk of transmission of the infection.) Mike Miller, a Colorado Parks and Wildlife veterinarian, describes the telltale signs of infection in animals as follows:8
"As the central nervous system damage progresses, behavioral signs become more apparent. The animals aren't paying attention. They may not respond. They may lag behind. As things progress more, they have more trouble moving. They carry their head differently. They don't pick their feet up the way they should.
In the later stages, some animals pick up a habit of drinking lots of water. Some develop a difficulty swallowing. They tend to feed inefficiently. They're sort of mouthing the plants but not biting and swallowing the way a normal animal would."
Hunters Urged to Test All Carcasses and Share Results
Other proposed strategies to contain the disease include "Discouraging large gatherings of deer, elk and moose to slow the spread of CWD via exchanges of animal body fluids. Tactics include removing of salt licks … and enforcement of rules prohibiting baiting of big game." They will also tighten requirements for safe disposal of infected carcasses at landfills and prohibit the transport of carcasses between states. Matt Dunfee, director of the Chronic Wasting Disease Alliance issued the following statement:9
"If you are a hunter, we will need you to hunt because we need the samples you can provide. If you are a wildlife enthusiast and want to see healthy deer and elk, you'll need to push for funding for studies and for implementing all the recommendations in this plan for scientific management of CWD.
The challenge for the public will be allowing these animals to be harvested. This disease does not go away. There is no vaccine. It is always fatal. And the only hope we have to manage it is to try to keep the prevalence low."
Importantly, hunters are urged to test all meat before consuming it. The idea that a healthy-looking animal is going to be free of the disease is a foolhardy approach at best. "The vast majority of the time hunters find out their animal has CWD, they're shocked, because it looked great. It was moving just like everything else. It had great body fat," Dunfee says.10
The reason for this is because the disease develops over time. An animal may remain asymptomatic for up to two years. And, while some insist there's a strong species barrier between deer and humans, research linking the prion-like protein TDP-43 to neurological diseases in humans hint at a potential risk of eating contaminated venison.