Both bluetongue and EHD occur more frequently during drought years, possibly because deer concentrate around available water sources, which is also the breeding habitat for the gnats. White-tailed deer are most susceptible to these diseases and usually die within two to four days, but can survive up to two weeks, according to a WDFW statement. Mule deer do not typically die from these diseases, although there have been a handful of documented deaths this year.

Since the outbreak of two deadly drought-related wildlife diseases in August, there have been more than 500 reports of sick or dead deer in Eastern Washington.