Chronic Wasting Disease in Animals

How CWD spreads

Chronic wasting disease (CWD) is a type of prion disease that affects different species of animals with hooves, including deer, elk, moose, and reindeer. CWD does not appear to naturally infect cows, other livestock, or pets.

Prion proteins are normally found in the body. In rare cases, these proteins misfold, which causes serious symptoms in the animal or person affected and eventually leads to death. Scientists believe CWD prions spread between animals through body fluids like feces, saliva, blood, or urine. This can occur either through direct contact or indirectly through contamination of soil, food, or water.

As of August 2025, CWD has been reported in animals in at least 36 U.S. states and five Canadian provinces. It is also possible that CWD may occur in other states, but cases haven't been detected yet. Once CWD is established in an area, the CWD prions stay in soil and water for years. CDC expects the disease to continue to spread.

Nationwide, the overall rate of CWD in free-ranging deer and elk is low. However, in areas where CWD has been found for years or decades, infection rates may be much higher.

The U.S. Department of Agriculture regulates deer and elk raised on farms for meat. The agency operates a voluntary national CWD herd certification program. In the program, states and herd owners agree to take actions to decrease the risk of CWD in their herds. Privately owned herds that are not in the program may be at increased risk for CWD.

Signs and symptoms

CWD can infect farmed and free-range deer and elk of all ages. It may take months to years before an infected animal shows symptoms, which may include:

• Drastic weight loss (wasting)
• Stumbling or lack of coordination
• Drooling
• Listlessness (appearing "out of it")
• Excessive thirst or peeing
• Drooping ears
• Lack of fear of people

It is often difficult to diagnose an animal with CWD based on these symptoms alone. This is because many CWD symptoms also occur with other diseases and when animals aren't eating enough.

Research on CWD in animals

In external research labs, CWD has been shown to infect squirrel monkeys and mice that carry some human genes.

A study by Canadian and German scientists looked at whether CWD can be spread to macaques, a type of monkey. Macaques are genetically closer to people than any other animal that has been infected with CWD. A 2017 summary concluded that CWD spread to macaques that ate infected meat or brain tissue from CWD-infected deer and elk. This study contradicted a previous study that showed macaques were not infected with CWD by eating infected meat. It's not clear why the results were different.

To date, there is no strong evidence that CWD infects people, but these studies show that caution and additional research are warranted. Scientists are conducting studies to learn more about the potential risk to people who hunt or eat deer or elk meat, for example by determining if they are diagnosed with prion diseases more often than people who do not. Since it may take years to decades for symptoms to appear, we won't know the results for some time.