Chronic Wasting Disease: What Is the Fatal Disease and What Causes it?

by Jon D. B.
chronic-wasting-disease-deer-elk-what-is-the-fatal-illness-what-causes-it

The always-fatal Chronic Wasting Disease, or CWD, is an increasing cause for concern to wildlife conservationists and sportsmen alike. But what exactly is this relatively new illness, and what is causing its spread across North America?

For hunters, conservationists, and farmers alike, Chronic Wasting Disease has become a dominating presence. Recent news – from infection penetrating the U.S. National Elk Refuge, to cases surging among popular hunting states – is chock-full of concerning CWD headlines. While scientists have become familiar with more familiar with the disease in the past decade, it remains wildly unpredictable.

As the destructive illness continues to spread across the U.S. and Canada, Chronic Wasting Disease has become required reading for any who concern themselves with cervid (deer family) populations in North America. To help, Outsider’s resident wildlife technician is breaking down the fatal disease, its causes, symptoms, and everything else you’ll need to know of CWD.

Overview: What is Chronic Wasting Disease?

Firstly, Chronic Wasting Disease, commonly abbreviated CWD, is an always-fatal neurological disease prominent in white-tailed deer. Other closely related cervids, such as mule deerelk, and moose, are also susceptible to the disease.

Once contracted, CWD attacks the nervous system of its host, resulting in neurological deterioration of the animal until eventual death. The primary symptom in wildlife is progressive, drastic weight loss, or “wasting”. Other symptoms vary, but may include stumbling, excessive salivation, deterioration of senses, and resulting behavioral changes.

As for its discovery, CWD first became known through captive deer in a Colorado research facility in the late 1960s. The first wild cases didn’t appear until 1981. By the 1990s, however, its spread into northern Colorado and southern Wyoming had begun. In the decades since, Chronic Wasting Disease has been found in the wild cervids of 24 states so far. These include states in the Midwest, Southwest, and spotted areas of the East Coast, alongside two Canadian provinces.

“It is possible that CWD may also occur in other states without strong animal surveillance systems, but that cases haven’t been detected yet,” the CDC adds. “Once CWD is established in an area, the risk can remain for a long time in the environment. The affected areas are likely to continue to expand.”

Further facts, alongside the disease’s cause, affected species, its methods of contagion & spread, symptoms, danger to humans, and confirmed locations, are listed in detail below.

What Causes Chronic Wasting Disease?

According to USGS, Chronic Wasting Disease is caused by a misfolded protein called a prion. Prions are produced normally within all mammals for use in cells. Once used, prions are then recycled within the body.

These misfolded prions cause other normal prions to form abnormal shapes upon contact within the body. The misshapen, disease-associated prions are unable to be recycled within the body like normal prions. As a result, they accumulate within lymphatic and neural tissues – including the brain.

This slow process results in CWD, and the neurological deterioration of the host, until eventual killing any cervid who contracts it.

How Does CWD Spread?

As for how the disease spreads, CWD transmits directly from animal-to-animal through touch. It is the contamination of surrounding habitats, however, that scientists believe causes it to spread more rapidly. Everything from the urine and feces to the saliva and blood of an infected animal carries CWD contagions. As a result, any other animal to come in contact with an area contaminated by one or all runs risk of infection.

Moreover, the CDC states that “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.”

Indeed, CWD stays present in deceased animals long after their death.

Even more concerning is the incubation period for Chronic Wasting Disorder. CWD has an extended incubation period that can take from 18 to 24 months. During this time, animals behave and look normal and healthy. As such, it’s incredibly difficult to stop or slow CWD through early detection, as carriers appear “normal” for up to two years before obvious symptoms appear.

All of the above leads to far greater concern for captive conservationists, rehabilitators, and breeders. The CDC reports that the infection rate can be as high as 79% for captive herds. High rates of infection are less common in free-ranging deer and their relatives, however.

What Species Can Contract CWD?

It is a common misconception that CWD is only present in white-tailed deer. This, however, is unfortunately not the case. The entire North American Cervidae family of hoofed deer are capable of contracting the disease. These include:

  • Red deer
  • Mule deer
  • Black-tailed deer
  • White-tailed deer
  • Sika deer
  • Caribou / reindeer
  • Wapiti / elk
  • Moose

What are the Symptoms of CWD?

As a result of neurological deterioration, CWD suffers exhibit an onset of symptoms after the incubation period – when the disease begins to take its toll on the host.

The primary symptom in wildlife is progressive, drastic weight loss, or “wasting”. Other symptoms vary, but include stumbling, excessive salivation, deterioration of senses, and resulting behavioral changes.

These behavioral changes include: decreased social interaction, loss of awareness, and loss of fear of humans. Increased drinking and urination have also been observed.

The CDC lists the most prominent symptoms of CWD as:

  • drastic weight loss (wasting)
  • stumbling
  • lack of coordination
  • listlessness
  • drooling
  • excessive thirst or urination
  • drooping ears
  • lack of fear of people

It is often difficult to diagnose a deer, elk, or moose with CWD based on these symptoms alone because many of CWD symptoms also occur with other diseases and malnutrition. CWD is always fatal.

CWD does not appear to naturally infect cattle or other domesticated animals.

CDC

How Does CWD Affect Humans?

Outside of its impact on hunting game, local ecosystems, and the like, there is thankfully no strong evidence that Chronic Wasting Disease is transmissible to humans. The Centers for Disease Control does, however, warn not to consume meat from any animal testing positive for the disease. To this end, the CDC details:

“Strongly consider having the deer or elk tested for CWD before you eat the meat. If you have your deer or elk commercially processed, consider asking that your animal be processed individually to avoid mixing meat from multiple animals. If your animal tests positive for CWD, do not eat meat from that animal.

CDC

Where Has CWD Been Confirmed?

Chronic Wasting Disease has been found in the wild cervids of 24 states so far. These include states in the Midwest, Southwest, and spotted areas of the East Coast, alongside two Canadian provinces. The USGS‘s most recent map shows the current outlook for the disease. In addition, it breaks down where the disease is free-ranging or present in captive facilities.

In the U.S., Kansas, Colorado, Wyoming, Nebraska, Utah, Illinois, and Wisconsin have the highest rates of infection.

Click here to view the full map and check your area for local infections.

To stay up-to-date on all the latest on Chronic Wasting Disease and how it is affecting American wildlife, sportsmen, and conservationists alike, stay with us here at Outsider.com.

[Sourced: USGS, CDC]

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