The State of Deer and Elk: EHD vs. CWD (VIDEO)

It’s no secret. Epizootic hemorrhagic disease and chronic wasting disease have both reared their ugly heads in the last couple years and have impacted Idaho’s deer and elk in localized areas. While both diseases affect members of the deer family, there are some pretty significant differences between the two.

In the sixth installment of Fish and Game’s ‘State of Deer and Elk’ series, Stacey Dauwalter explains EHD and CWD and clarifies some of the misconceptions associated with each. Dauwalter is Fish and Game’s Wildlife Health Program Coordinator and has been involved in both the summer EHD outbreak in 2021 and the discovery of CWD during the fall of that same year.

What Is 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. Idaho experienced an outbreak of EHD during the summer and fall of 2021, which mostly impacted white-tailed deer in the Clearwater and Panhandle areas. 

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. 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, 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 epizootic hemorrhagic disease, check out Fish and Game’s EHD webpage.

What Is Chronic Wasting Disease?

Fish and Game received positive tests for CWD from two mule deer bucks taken by hunters in Unit 14 north of Riggins during October 2021. These were the first CWD-positive animals ever detected in Idaho. 

CWD is a fatal and contagious disease that affects the nervous systems of deer, elk, moose and reindeer. CWD is caused by a misfolded, infectious protein accumulating within the nervous system of deer, which ultimately causes death. 

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's CWD webpage.