The Division of Fish & Wildlife is again reassuring Delaware residents and hunters that an insect-borne disease that has been killing white-tailed deer throughout North America does not affect humans and has little long-range ramifications for the health of the state’s deer herd.
The disease—epizootic hemorrhagic disease, or EHD for short—is transmitted by small biting flies commonly called midges or “no-see-ums.” All known outbreaks of EHD have occurred in late summer and early fall, and are abruptly curtailed with the onset of frost which kills the midges and suspends the hatch of larvae.
EHD, also known as “blue tongue,” is the most significant disease afflicting white-tailed deer in North America but is also the best known and most widely studied, having first been identified in 1955 with regular, almost annual outbreaks since. By Delaware standards, last year was an uncommonly severe year, with 132 EHD-related deer fatalities.
“We recently received the first report of a suspected EHD deer casualty this year, so we want to begin educating hunters and the public about the disease," said Game Mammal Biologist Joe Rogerson. "While the virus is often fatal, it apparently did not have much of an impact on the Delaware deer population, as the overall harvest from the 2007-2008 season was the third all-time highest. If EHD had significantly impacted the deer herd, we would have expected the harvest to be down, but we didn’t see that."
Humans cannot be infected by EHD, nor can the disease be transmitted by consuming venison from afflicted animals. (Hunters are advised, however, to avoid eating visibly sick deer because they may be stricken by a secondary infection that could affect people, Rogerson noted.)
No pesticides can be sprayed to kill the insects that cause EHD, nor can white-tailed deer be vaccinated against the disease. “We are in a position of allowing nature to run its course and waiting for a hard frost to kill the midges” Rogerson said.
Symptoms of the disease in deer resemble another sickness, chronic wasting disease, or CWD, which is not yet known to have occurred in Delaware. Afflicted animals exhibit pronounced swelling of, and bleeding from the head, neck, tongue and eyes. Deer die from EHD as soon as one day after contracting it, but more commonly survive for three to five days. Carcasses are often recovered near water and the EHD outbreaks are most often associated with periods of drought.
As with many viruses, not all deer will die once they are infected. Some will be able to enact an immune response and fight off the infection. These deer will then have the antibodies to ward off any potential future infections. The virus deteriorates less than 24 hours after a deer dies, and cannot be spread from carcasses. EHD does not generally have a significant impact on livestock.
Hunters or members of the public who see a deer carcass with no readily apparent cause of death are asked to report it to Rogerson by calling 302-735-3600. “While nothing can be done to prevent the further spread of EHD until colder weather halts the midges from infecting deer, the Division would like to document deer mortality for research and to obtain data for future references to the disease,” he said.
Even as high as the figures were for the state last year, Delaware's deer suffered lightly in 2007 from EHD by comparison to Pennsylvania, where several thousand deer died, and neighboring Mid-Atlantic states, where deer deaths numbered in the hundreds. Deer died from EHD in all three counties in Delaware, but mortality was most concentrated in lower Kent County, outside Harrington and Greenwood.