The virus has an incubation period of approximately one week, during which the animal may transmit the virus to biting midges. After the development of symptoms (which include internal hemorrhage, weakness, high fever, bruising, and dyspnea) the animal dies within 8 to 36 hours."
We've had a few episodes of this here in Virginia, also. If memory serves me right, EHD has a correlation with drought conditions. Water levels drop and these midges reproduce in the exposed mud and infect the deer when they come to drink.