Hemorrhagic disease, which is spread by tiny, biting insects, broke out in late summer in herds in more than a dozen counties in the northwestern corner of the state. The counties most impacted are Surry, Wilkes and Caldwell, and the heaviest occurrence of fatalities is in areas along the base of the Appalachian escarpment the eastern slope of mountain ranges that rise up to the eastern continental divide. Other counties with a significant number of reported fatalities include Mitchell, Burke, Alleghany and Cleveland.
Chris Kreh, a wildlife biologist with the N.C. Wildlife Resources Commission, estimated that mortality may run between 30 and 50 percent in most areas, even higher in the most-affected spots in those counties. The disease may have already killed more deer than hunters did in the 2011-12 season, and a steep drop in the early season archery harvest bears that out.
"We believe the disease mortality will be one to two times more than the hunting mortality," Kreh said.
The Commission cannot change regulations or bag limits before muzzleloader and gun seasons open in the affected areas. Biologists are hoping that hunters take into account the depressed state of the herd when deciding how many deer to harvest.
"There will be (fewer) opportunities for hunters to harvest deer this fall. I think there will be a strong, voluntary holding-back on the harvest of deer this year by hunters," Kreh said. "Landowners and hunt clubs need to be aware of the significant disease mortality and adjust their doe harvest accordingly."
Through the first eight days of archery season, according to Kreh, the harvest was down 57 percent in Wilkes County and, 45 percent in Surry County, compared to the period in the 2011 season. Through the entire 2011-12 season, hunters in Wilkes County took 9.7 deer per square mile, and hunters in Surry County took 6.8 per square mile. Kreh estimates the disease mortality appears to be 12.4 deer per square mile, roughly two-thirds does and one-third antlered bucks.
Humans cannot contract hemorrhagic disease, either through contact with biting flies or "midges" or through consumption of venison from affected animals. The disease appears in several different strains, and biologists say the strain that has infected deer this summer and fall is among the quickest-acting, most virulent. The time between infection and death, Kreh said, may be as short as three days.
Deer that are infected develop an extremely high fever; they often react by going to water sources – creeks, rivers, ponds and lakes – which accounts for the fact that most dead animals are found in water.
The disease is cyclical, appearing in different strains every four or five years in different parts of North Carolina and the Southeast. Less-virulent strains may provide some immunity to affected deer, and the immunity can be passed down from does to their offspring. The disease also shows up more often in years with hot, wet summers, especially following mild winters. These conditions promote the hatching or more of the tiny insects, which go by the biological name colicoides.
"This is the most important disease of the whitetail deer; it's likely been killing deer as long as deer have been around," Kreh said. "The frequency of when it hits varies greatly, and it's not a disease brought on by an overpopulated deer herd.
"It's primarily a disease of the Southeast; the farther south and east you go, the worse it becomes. The farther north and west you go in the area, it's less frequent, the deer have less immunity, and you get higher mortality."
The first freeze of the fall usually puts an end to the disease, killing the insects, which is why biologists describe hemorrhagic disease as being most prevalent from July through September.