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Idaho Fish and Game

A group of deer in the City of Cascade approach the driver's side window of a vehicle during the winter of 2023.

Chronic Wasting Disease (CWD) and Epizootic hemorrhagic disease (EHD) are different, and here's how they differ


The EHD outbreak that occurred over summer and fall has likely ended, CWD has been detected for the first time in Idaho

Idaho had an outbreak of epizootic hemorrhagic disease (EHD) during summer, mostly in white-tailed deer in the Clearwater and Panhandle areas. The EHD outbreak killed deer throughout the summer and fall. Idaho Fish and Game also received positive tests for Chronic Wasting Disease (CWD) from two mule deer bucks taken by hunters in Unit 14 north of Riggins during October. These were the first CWD-positive animals ever detected in Idaho. These are two separate and unrelated diseases. 

Chronic Wasting Disease

Chronic Wasting Disease is a fatal and contagious disease that affects the nervous systems of deer, elk, moose and reindeer. CWD is believed to be caused by abnormal, misfolded forms of the prion protein accumulating within brain cells, which causes progressive damage to those cells and brain damage.  

According to the U.S. Centers for Disease Control, to date, there have been no reported cases of CWD infecting people. However, hunters are encouraged to have their animals tested for CWD, and not consume any animal that tests positive for CWD. 

CWD has a very long incubation period (time between infection and observable disease) that typically takes at least 10 months for a deer or elk to show signs of illness. Experts believe CWD proteins (prions) likely spread between animals through feces or body fluids like saliva, blood or urine, either through direct contact, or indirectly through environmental contamination of soil, food or water. These CWD proteins can remain contagious in the environment for 10-plus years.

Symptoms of CWD include excessive salivation, drooping head/ears, tremors, extremely low body weight, and unusual behavior, such as showing no fear of humans and lack of coordination.  CWD cannot be diagnosed strictly by symptoms because other diseases, or conditions, can also cause an animal to exhibit similar symptoms and behavior.

For more information on CWD, including how to get a harvested animal tested, see Fish and Game webpage

Epizootic hemorrhagic disease

Epizootic hemorrhagic disease occurs sporadically in Idaho, typically during hot summers and during drought. It most commonly affects white-tailed deer, but can also affect mule deer. 

The disease is spread by gnats, and the severity of the disease is largely dependent on the level of herd immunity and animal density. A hard frost typically ends an EHD outbreak, so the current outbreak is likely over, or close to it. Some deer survive EHD infections, and herd immunity and survival is higher in areas with long historical exposure to EHD. 

Symptoms of EHD in deer include a loss of appetite and wariness, swelling around the head and neck, dehydration and weakness, increased respiration rate, excessive salivation, rosy or bluish color of mouth and tongue, blood flecks may occur in the urine and feces. In severe cases, a bloody diarrhea can develop. Deer that are infected may show lameness and a tendency to avoid direct sunlight. An increase in body temperature can cause deer to seek cool places, such as in and around water.

There is no established public health risk associated with handling or eating animals infected with EHD. 

For more information on EHD go to