EHD/BT has more impact on white-tailed deer than other naturally occurring disease I have seen. It is a virus that is spread by one vector, a tiny "no-see-um" midge (true fly family) of the genus Culicoides. The degree of sickness resulting from an infected bite depends on the virulence of the virus at that stage. We look at symptoms, clinical signs and disease progession in 3 forms; 1)peracute is very rapid sickness leading to death (hours); 2)acute is more classic type development with slow death (days-week)); 3)chronic is very slow or apparent recovery (months-year). More incidence of chronic is being suspected all the time...the infected deer may not die until the next hot season. The most common host of this pathogen is cattle. In some SW states, 90% of all sampled cattle test positive for EHD, but never get sick or show symptoms.
Although the female midge(the only one that bites) can theoretically pass the disease into unborn eggs, most EHD comes from an adult female midge that bites infected cattle, then deer.
The disease runs parallel with hot temps because of the correlation with the life cycle of the midge in most regions (June - October). The midge larvae are aquatic, like mosquitoes, and depend on fluctuating water levels (wet-dry, high-low) to complete their metamorphosis. They prey on large warm-blooded hosts, usually within 300ft of birthplace. Midges come out in very early morning or at dusk; they dislike direct sunlight or wind. The males hide in nearby vegetation and drink plant juice.
EHD outbreaks can cause 25%-50% mortality in wild herds.
Vector control is the best way to keep midges at bay around your wetlands. Permectrin, water soluble, 10% concentrate in a sprayer will kill midges and is safe on visiting deer.
I have done extensive field research on this disease and its control--info available on request.
Dan
