Chronic Wasting Disease, often abbreviated as CWD, is an incurable, fatal condition involving misfolded proteins called prions. It is known to primarily affect cervids, which make up the deer family of species.
What is Chronic Wasting Disease in Deer?
Proteins have very specific shapes, and these shapes are critical to their proper functioning in living things. In CWD, a protein called PrPC becomes misfolded, and this misfolded protein is known as PrPCWD.
This means CWD is a prion disease, or transmissible spongiform encephalopathy (transmissible = infectious to others, spongiform = the sponge-like, hole-ridden appearance of a brain infected with the disease, encephalopathy = disease of the brain), just like other diseases including Mad Cow Disease (in cattle, formally known as bovine spongiform encephalopathy) and Creutzfeldt-Jakob disease (in humans). Although the prions of infected deer can be found in tissues outside the brain, the disease is primarily neurodegenerative, meaning it leads to the deterioration of the brain itself.
How do Deer Get Chronic Wasting Disease?
Deer can become infected with CWD via their environment or other deer. For example, the prions are excreted in the urine and feces of an infected deer, as well as in their saliva. Unfortunately, prions are persistent and can survive for years in the surrounding soil. This means that even years after an infected deer has passed away, the infectious prions can still be alive in the environment where other healthy deer live, potentially infecting them as well.
While not confirmed, evidence of CWD in very young deer has been noted, suggesting that perhaps the disease can be passed on from mother to offspring. It is difficult to know, however, if this is truly an instance of transmission from the mother, or if the young deer were simply born into a heavily contaminated environment, exposing them very early on to prions.
There is no single cause of transmission for CWD, but the primary mode is believed to be direct contact with another deer who happens to be infected, as well as contact with the environment the sick deer lives and roams in.
Additionally, it is not certain where the disease originated from, but the most plausible hypothesis is that it evolved from scrapie, which is a prion disease found in sheep.
What are Signs of Chronic Wasting Disease in Deer?
CWD can actually incubate in an infected deer for years; no symptoms will be observable as the disease is essentially dormant. However, once active, there are several symptoms that become noticeable in a relatively short period of time, with death occurring on average within a few months.
One of the earliest signs is weight loss. Many deer with CWD also no long fear humans. Coordination becomes worse as well, and the deer might appear to stumble or be unable to walk normally. Additional symptoms are unlikely to be noticed without close observation but include things like excessive thirst and/or urination or even depression.
Once a deer has died, however, it is not possible to look at it and tell if it had CWD or not. Diagnosing CWD requires advanced methods and tools, and is best done shortly after death occurs.
Where is Chronic Wasting Disease Found?
CWD was first discovered in 1967 in the United States, and is currently found in 29 total states according to the CDC. In Canada, CWD can be found in 3 provinces, while in Asia it is found in South Korea and in Europe CWD is present in the countries of Finland, Sweden, and Norway.
The rate of CWD has increased and appears to be continuing to rise, despite attempts to slow the spread.