Chronic Wasting Disease Q&A

What is CWD?

CWD is a fatal neurodegenerative disease that can spread among wild and farmed cervids.  Classical clinical signs of the disease include:

  • Weight loss, drooling, head drooping, erratic behavior, and neurological abnormalities
  • However, most infected cervids look perfectly normal.  Farmed raised deer have a high level of nutrition so weight loss may not be observed.
  • Though not considered classic signs of CWD, on some farms, cervids later testing positive for CWD show clinical signs of pneumonia or bloat, or other nonspecific signs of illness.

CWD is spread by infected animals shedding CWD prions, which are misfolded proteins.

  • CWD prions can be spread through saliva, urine, feces, and blood of infected animals (including some which do not show clinical signs of illness), and tissues of infected animals that died.
  • CWD prions can be spread through wild animals and environmental contamination via soil, plants, and water.
  • CWD prions can persist for years in the environment.

How to detect CWD?

CWD is difficult to detect as infected animals may not show signs after becoming infected for months to years. 

  • During this time, infected cervids can still infect other cervids and contaminate the environment.
  • Animals showing these signs can be tested using approved tests at an approved State Diagnostic Lab.  This usually requires collection of samples that can only be collected from the animal after death (retropharyngeal lymph nodes and/or brainstem); there currently are no federally validated CWD tests for routine surveillance of live animals.  
  • Other tests are used for research purposes, but have not yet been validated and are not yet available for use by the public.

What can you do to stop CWD?

Testing clinically affected animals is not an effective disease control strategy by itself because infected cervids can infect other cervids before showing clinical signs of illness.

Preliminary evidence suggests that selection of breeding stock with reduced genetic susceptibility to CWD may be part of an effective control strategy, though research studies to evaluate its effectiveness have not yet been completed.

The remaining best control strategy is to reduce the risk of exposure of farmed cervids to the CWD infective prion protein.  How to do this?

  • State regulatory policy - State rules are in place that ban risks of spread from known CWD-infected cervid operations, including movement of cervids or sharing of equipment to/from these farms, requiring 8 ft high perimeter fences to prevent direct contact between wild and farmed cervids, mandatory identification of farmed cervids, and required testing of farmed cervids that die from disease or other natural causes using samples tested at a State Lab.  Though rules differ slightly from state to state, cervid producers who intend to move cervids across state lines need to follow federal guidelines.  There are legal ramifications to individuals that knowingly fail to follow these rules.
  • It is not enough to rely on State regulatory policy measures alone to prevent CWD risks, as those are intended to prevent transmission through known high-risk pathways of transmission only.  Cervid producers should take additional biosecurity measures to further reduce the risk of introduction of diseases to animals on their operation, based on their own situation.

What is biosecurity?

Biosecurity refers to plans and procedures you implement to reduce the risk of a hazard, including an infectious disease like CWD, from entering your operation (being carried onto your place by animals, equipment, vehicles, or people).

Can biosecurity prevent CWD introduction to your farm?  Can it stop transmission if the infective material is in the soil? Is it always, and already, there?

How to think about risk?  It is important to recognize that we live in a world full of risks, and we typically cannot totally eliminate all of these risks (reduce the likelihood of these risks to zero).  Every time we take the wheel of our car, we are exposed to the risk of a car accident.  While we cannot totally eliminate this risk, we can take steps to greatly minimize this risk through use of safe driving practices (such as follow the ‘rules of the road’, drive within posted speed limits, don’t drink and drive). 

Biosecurity practices work similarly.  Some guiding principles for effective biosecurity programs:

  • Biosecurity works like insurance:  the more you invest in appropriate preventive practices, the more you can reduce your risk.  Biosecurity doesn’t come with a guarantee, but reduces the likelihood of a bad event happening (in this case, CWD introduction to your operation).
  • Biosecurity practices need to address the primary risks or hazards to your operation.  For CWD prevention, it is critical to consider all of the potential pathways of transmission, and highlight those which pose the greatest likelihood of occurrence.  Biosecurity needs to be matched with your specific situation, which may be different from risks to other operations.

More information about CWD can be found: