Biologists explore deaths of deer

With the opening of the first deer hunting seasons just weeks away, news of white-tailed deer dying in two southwestern Pennsylvania counties has raised concern among both the hunting public and Game Commission biologists. Since early August more than 50 deer have died in Greene and Washington counties.

Postmortem studies are under way at Penn State University and the Southeastern Cooperative Wildlife Disease Study at the University of Georgia. Dr. Walter Cottrell, Game Commission wildlife veterinarian, says, “While we must wait for test results to confirm just what caused these deer to die, at this time, we suspect that the deer died of epizootic hemorrhagic disease (EHD), based on the field signs that we are seeing.”

The same thing is happening in Tennessee. Alan Peterson, a wildlife biologist with the Tennessee Wildlife Resources Agency, has received reports of EHD from across the state during the past few weeks. Biologists at the University of Georgia confirmed EHD in Tennessee, and said the outbreak is affecting deer all over the southeastern United States. Perhaps weather plays a role.

About the disease

EHD is a blood-borne viral disease transmitted to deer by a species of biting midge (a mosquito-like fly) that is common across the South. Because much of the South is in the midst of a three-year drought, water is scarce, and many deer are forced to drink from the same water sources. That concentrates the deer so the midges can infect more individuals in one place.

Jerry Feaser, a Game Commission spokesman, suggests that these midges may have traveled to Pennsylvania on north-bound weather fronts. He said these flies can’t survive Pennsylvania winters, so the disease should not persist in the state. The Game Commission also points out that EHD is not infectious to humans, though severely infected deer should not be eaten.

When deer are infected with EHD, they begin showing symptoms within seven days. Deer with milder infections develop a high fever and seek out water immediately. They often have pronounced swelling of the head, tongue, neck and eyelids and may have trouble breathing.

Fortunately, as many as two-thirds of the deer infected with the disease survive — and once they’ve had the disease, they develop a natural immunity that keeps them from being infected again. And female deer that survive the disease often pass the immunity to their fawns through their milk.

Outbreaks

The first occurrence and identification of EHD occurred in 1955 when several hundred white-tailed deer died in both New Jersey and in Michigan. Since then outbreaks of EHD have occurred in white-tailed deer in many northern and Midwest states: South Dakota (1956), Michigan (1974, 2006), Nebraska (1976, 1981), Wyoming (1976), Kansas (1976), Missouri (1980), Pennsylvania (2002), Wisconsin (2002). Outbreaks occur almost annually in the Southeastern states.

A common observation in outbreaks involving large numbers of deer is that they are single episodes that do not recur. That’s the good news. The bad news is that when outbreaks occur in the North, the disease is more virulent, and the death rate is higher. Apparently southern deer populations are more genetically resistant to ERD.

The name epizootic hemorrhagic disease describes its primary symptoms. Hemorrhages vary in size. The most often affected organs are the heart, liver, spleen, kidney, lung and intestinal tract. Extensive hemorrhaging results from impaired blood-clotting ability and degeneration of blood vessel walls.

Symptoms

White-tailed deer develop signs of illness suddenly about seven days after exposure. Initially, deer lose their appetite and fear of man, grow progressively weaker, often salivate excessively, develop a rapid pulse and respiration rate, and finally become unconscious. Hemorrhage and lack of oxygen in the blood results in a blue appearance of the oral mucosa, so the disease is sometimes called “bluetongue.” Eight to 36 hours after the onset of observable symptoms, deer pass into a shocklike state, collapse and die.

State wildlife agencies rely on public vigilance to report dead or dying deer; otherwise outbreaks of EHD could go undetected.

One final note: Dr. Cottrell reports that EHD is not related to chronic wasting disease, a neurological disease of deer that has made headlines the last few years.

XSend questions and comments to Dr. Scott Shalaway, R.D. 5, Cameron, W.Va. 26033 or via e-mail to sshalaway@aol.com