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, 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, 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.