Prion diseases, or transmissible spongiform encephalopathies (TSEs), are progressive neurodegenerative disorders caused by prions: pathogenic agents that can cause abnormal folding of specific proteins which are found most abundantly in the brain, causing brain damage and neurologic symptoms. Examples of TSEs include mad cow disease, Creutzfeldt-Jakob disease, and chronic wasting disease.
Chronic wasting disease (CWD) is a prion disease affecting the nervous system of farmed and wild cervids (i.e. deer, elk, moose, and caribou) in North America. CWD has also been documented in Norway and South Korea. Symptoms include weight loss, stumbling, listlessness, nervousness, trembling, repetitive behaviors, increased drinking and urination, excessive salivation, and grinding of the teeth; however, an animal can remain asymptomatic for over a year after infection [source]. CWD is always fatal and there is no known cure or treatment.
How do prions cause disease?
Proteins are made of chains of amino acids. Multiple protein molecules can assemble together in different ways, and these chains fold into complex three dimensional structures. Different structures and shapes perform different functions. The proper assembly of these protein structures is called its native state.
But if a protein is folded in the wrong way, it starts to behave differently and/or no longer performs its intended function. These misfolded proteins can interact with surrounding proteins, starting a chain reaction and an accumulation of misfolded proteins. As these misfolded proteins build up, that means there are less and less functional proteins and more and more dysfunctional proteins present in the cell, resulting in a damaged cell.
This is how prions work: they facilitate the misfolding of specific proteins in brain cells, resulting in cell damage and neurodegenerative symptoms.
However, one thing that sets CWD apart from other prion diseases is that it is not restricted to brain tissues; CWD prions can be found in other types of tissues, bodily fluids, and feces. This allows for direct animal-to-animal infection.
How is CWD transmitted?
Cervids can become infected by direct (animal to animal) or indirect (environmental) exposure.
Studies show CWD can be transmitted environmentally via infected carcasses [source], bodily fluids [source], and infected soil [source]. Another study has shown that CWD can survive passage through the digestive tract of coyotes and will be present in coyote feces up to 3 days after ingestion of an infected prey animal [source]. This can contribute to the spread of CWD throughout previously unaffected geographical areas.
Where has CWD been documented?
At this time, the North American geographic range of CWD includes 22 US states and 2 provinces in Canada. This range is expected to expand.
Can CWD infect non-cervid animals?
There have been no reports of natural interspecies CWD infection amongst non-cervid animals. However, interspecies infections have been successfully facilitated experimentally.
Although canines seem to be immune to prion diseases in general [source, source], felines [source] and mustelids [source] are susceptible to other types of prion diseases, as are humans [source]. At this time, there have been no reports of humans or dogs infected with CWD, but cats and ferrets have been infected experimentally.
However, nonhuman primates (squirrel monkeys) have been successfully infected experimentally [source], and macaque monkeys have been infected after eating infected venison [source], indicating that there may be a risk of potential for human infection of CWD.
Domestic cats have been experimentally infected with CWD after eating infected venison brain [source]. Ferrets have also been experimentally infected with CWD [source], but ferrets and other species of the mustelid family (mink) seem to be resistant to infection from consuming infected meat.
What precautions should be taken?
Hunters have been advised not to consume brain, spinal cord, eyes, spleen, tonsils, or lymph nodes of cervids, and to bone out the meat and avoid sawing through bone, especially the spine [source]. The same precautions should be extended to our raw fed pets, especially cats, and especially if the animal was harvested from an area where CWD has been reported.
At this time, there is no indication of risk associated with feeding raw venison meat other than the parts mentioned above, especially if the animal was harvested from an area where CWD has not been reported. However, caution should be exercised (especially with cats) and owners should stay up to date on CWD cases in their area and/or only purchase from a supplier that tests for CWD.
Out of an abundance of caution, I would recommend against feeding cervid bones, brain, spinal cord, spleen, lymph nodes, eyes, or tonsils from areas where CWD has been reported to any animal unless the cervid has been tested for CWD and test results came back negative. I also recommend against feeding any cervid meat to cats if it was harvested in an area where CWD has been recorded unless the animal has tested negative for CWD.