Disease outbreak affecting Wyoming deer, pronghorn

A group of pronghorn on the sage-steppe of Wyoming. Tom Koerner/USFWS

An outbreak of epizootic hemorrhagic disease is threatening wildlife in Wyoming. Wyoming Game and Fish Department biologists say the disease is not uncommon in times of drought and hot weather, but this year appears like it may be on track for a more serious outbreak.

EHD is caused by a virus that primarily affects white-tailed deer (Odocoileus virginianus) and pronghorn (Antilocapra americana). It is more likely to spread when wildlife congregate around small water holes where the disease-carrying biting midge lives. Transmission only occurs when a host animal is bitten by a midge, not through animal-to-animal contact.

EHD typically occurs in the fall, especially in dry conditions coupled with drought. As water holes shrink, animals become more concentrated, helping midges transmit the disease. While the disease can be deadly, not all animals exposed to the virus die, and some develop an immunity. Humans are not at risk of contracting the disease. Threats from the virus fade after the first hard frost kills off the midge population.

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