The horrible disease called chronic wasting disease (CWD) is spreading among deer, moose, and elk throughout the US and Canada, and reindeer in Norway. This prion disease is similar to "mad cow disease" (bovine spongiform encephalopathy) in cattle, scrapie in sheep and goats, or Creutzfeldt-Jakob disease in humans. In CWD the brains become progressively like sponges - riddled with holes, along with deterioration in brain function, behavioral changes, and eventually death. Especially worrisome is that it is an infectious disease.
The Centers for Disease Control (CDC) reported in January 2019 that chronic wasting disease has been reported in deer, moose, and elk across 26 US states and 3 Canadian provinces - in both free ranging herds and also some captive herds (such as in ranches and game farms). The following excerpts are from the CDC site on Chronic Wasting Disease (CWD):
Chronic wasting disease (CWD) is a prion disease that affects deer, elk, reindeer, sika deer and moose. It has been found in some areas of North America, including Canada and the United States, Norway and South Korea. It may take over a year before an infected animal develops symptoms, which can include drastic weight loss (wasting), stumbling, listlessness and other neurologic symptoms. CWD can affect animals of all ages and some infected animals may die without ever developing the disease. CWD is fatal to animals and there are no treatments or vaccines.
To date, there have been no reported cases of CWD infection in people. However, animal studies suggest CWD poses a risk to some types of non-human primates, like monkeys, that eat meat from CWD-infected animals or come in contact with brain or body fluids from infected deer or elk. These studies raise concerns that there may also be a risk to people. Since 1997, the World Health Organization has recommended that it is important to keep the agents of all known prion diseases from entering the human food chain.
Nationwide, the overall occurrence of CWD in free-ranging deer and elk is relatively low. However, in several locations where the disease is established, infection rates may exceed 10 percent (1 in 10), and localized infection rates of more than 25 percent (1 in 4) have been reported. The infection rates among some captive deer can be much higher, with a rate of 79% (nearly 4 in 5) reported from at least one captive herd.
The big question is : Can humans get this disease from animals with chronic wasting disease? What if you eat the meat of a diseased animal? Currently there is no real evidence that humans can get it from eating infected meat (studies are ongoing), but...the disease has a time lag of years. Years. And animal studies suggest that transmission can happen between some species (at least the animals studied).
Another scary thought is that researchers feel that even after an animal has died, the prions shed by the animal are still there in the soil for very long periods (years!). One researcher (Dr.Zabel) has suggested that controlled burns (fires) of infected fields or areas could eliminate the prions left behind (by animal mucus/saliva, urine, and feces, and decaying carcasses) on plants and soil - this could stop the spread to other animals. Luckily some researchers are also discussing/looking at vaccines for deer to prevent the spread.
The CDC suggests that hunters have the animals they've killed tested for the disease in areas where it's found before they eat the meat, to wear rubber or latex gloves when handling the meat, and to not use household or kitchen knives when cutting up the meat, and to not eat any meat that tested positive for CWD. They also list some other suggestions. In other words, they're worried. Really worried.
If CWD could spread to people, it would most likely be through eating of infected deer and elk. In a 2006-2007 CDC surveyExternal of U.S. residents, nearly 20 percent of those surveyed said they had hunted deer or elk and more than two-thirds said they had eaten venison or elk meat. However, to date, there is no strong evidence for the occurrence of CWD in people, and it is not known if people can get infected with CWD prions.
Hunters must consider many factors when determining whether to eat meat from deer and elk harvested from areas with CWD, including the level of risk they are willing to accept. Hunters harvesting wild deer and elk from areas with reported CWD should check state wildlife and public health guidance to see whether testing of animals is recommended or required in a given state or region. In areas where CWD is known to be present, CDC recommends that hunters strongly consider having those animals tested before eating the meat.
From the CDC Chronic Wasting Disease Transmission page: Scientists believe CWD proteins (prions) likely spread between animals through body fluids like feces, saliva, blood, or urine, either through direct contact or indirectly through environmental contamination of soil, food or water. Once introduced into an area or farm, the CWD protein is contagious within deer and elk populations and can spread quickly. Experts believe CWD prions can remain in the environment for a long time, so other animals can contract CWD from the environment even after an infected deer or elk has died.
The CWD prion has been shown to experimentally infect squirrel monkeys, and also laboratory mice that carry some human genes. In addition, a study begun in 2009 by Canadian and German scientists is evaluating whether CWD can be transmitted to macaques, a type of monkey that is genetically closer to people than any other animal that has been infected with CWD previously. On July 10, 2017, the scientists presented a summary of the study’s progress (access the recorded presentationExternal and slides Cdc-pdf[PDF 3.88MB]External), in which they showed that CWD was transmitted to monkeys that were fed infected meat (muscle tissue) or brain tissue from CWD-infected deer and elk. Some of the meat came from asymptomatic deer that had CWD (i.e., deer that appeared healthy and had not begun to show signs of the illness yet). Meat from these asymptomatic deer was also able to infect the monkeys with CWD. CWD was also able to spread to macaques that had the infectious material placed directly into their brains.
This study showed different results than a previous study, which had not shown successful transmission of CWD to macaques. The reasons for the different experimental results are unknown. To date, there is no strong evidence for the occurrence of CWD in people, and it is not known if people can get infected with CWD prions. Nevertheless, these experimental studies raise the concern that CWD may pose a risk to people and suggest that it is important to prevent human exposures to CWD.
Additional studies are under way to identify if any prion diseases could be occurring at a higher rate in people who are at increased risk for contact with potentially CWD-infected deer or elk meat. Because of the long time it takes before any symptoms of disease appear, scientists expect the study to take many years before they will determine what the risk, if any, of CWD is to people.