Chronic Wasting Disease (CWD) is a neurological disease caused by a prion found in cervids. The prion is a transmissible spongiform encephalopathy (TSE) that is similar to bovine spongiform encephalopathy (BSE), or “mad cow disease,” in bovines. The disease is thought to be non-zoonotic, but it is still advised that people not consume infected venison. It is also not thought to have an effect on livestock. The disease was first found in captive populations in the 1970’s, with later speculations about wild origins going back more than 40 years prior. Little is known about this disease, how it is transmitted and its impact on animal populations, so research is being conducted to attempt to answer these questions. CWD is more common in adults but is not isolated from yearlings; it is a progressive disease and is always fatal.
Little is known about transmission, but it is thought to be contagious through direct contact between animals or possibly through contaminated water or feed sources. However, once infected, the prion works on the central nervous system to convert normal cellular proteins into abnormal proteins. Because of its small size, it does not instigate any inflammatory responses from the immune system like other infections normally would. This means the disease is undetectable by the immune system, making it especially hard to know if an animal is infected during early onset. The long incubation time of at least 16 months causes further uncertainty.
- Long-term weight loss due to gradual disinterest in food
- Excessive drinking and urinating (late stages)
- Decreases sociability
- Lowered head and blank look
- Repetitive walking in patterns
- Over-excitability and nervousness (elk)
- Brain, lymphoid and tonsillar lesions (once deceased and necropsied)
- Aspiration pneumonia (not confirmed but a common associated disease; might be the actual cause of death)
CWD is currently endemic to northeastern Colorado and southeastern Wyoming. It has been found in a few states east of the Mississippi River, but is concentrated primarily in the central and midwestern U.S. In total, CWD has been recorded in 21 U.S states and 2 Canadian providences. The range is expected to grow.
Species of Concern
Cervids, a group of unguilligates (hoofed animals), consist of species of deer, moose and elk. Species of concern for CWD in the U.S include:
- White-tailed deer: Most of the country and southern Canada, excluded in very southwestern states in the U.S
- Mule deer: Western North America
- Elk: Primarily in western North America
- Moose: Northwestern U.S and almost all of Canada
There is no known cure or clinical test in living cervids for CWD. Although CWD is not thought to be transmissible to humans through meat handling or consumption, it is still recommended that infected meat not be consumed. Little understanding of the prion makes long-term effects of CWD and how it will effect population management, hunting and environmental management are unknown. Uncertainty in diseases, especially one as fatal and undetectable as CWD, present extreme risk for population, environmental and, possibly, human health. Hunting is also a source of revenue for state governments, and cervids are America’s most popular game species. Effects on population would have effects on hunting quotas, licensing and ultimately state economies. More research is being conducted to better understand this disease, however it is not know what damage may have already been done.
CDC. (2015, February 06). Chronic Wasting Disease (CWD). Retrieved April 21, 2017, from https://www.cdc.gov/prions/cwd/index.html
Chronic Wasting Disease Alliance. (n.d.). Chronic Wasting Disease FAQ. Retrieved April 21, 2017, from http://cwd-info.org/faq/
NWHC. (2016, May 19). Chronic Wasting Disease (CWD). Retrieved April 21, 2017, from https://www.nwhc.usgs.gov/disease_information/chronic_wasting_disease/