Hemorrhagic Disease: The Deer Plague of the 21st Century
By Mike Lambeth
Deer are prolific animals that have expanded their territories to now inhabit 48 of the 50 states, with huge populations in Canada and Mexico also. Their populations in most states have bulged with such explosive growth, that they have attained near nuisance status in some metropolitan areas.
With this huge growth trend, deer have become more susceptible to a plethora of parasites and diseases, however, studies have shown that deer are very resilient and a very small percent fall victim. Nonetheless, in the last 10 years several diseases have raised the awareness of hunters and game managers to some of the potential threats faced by America’s most popular game animal.Hemorrhagic Disease
Hemorrhagic disease is a generalized name for both epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) - two diseases in which whitetail, blacktail, and mule deer sometimes fall prey. Together, these viruses kill more deer than any other. These diseases kill nearly 50 to 90 percent of all deer infected and are spread by a small biting midge fly, also known by the names of “gnats” or “no-see-ums.” The disease can also be found in cattle and goats, although both animal groups show very little signs of being affected, and have very low mortality. Studies have shown that sheep are only susceptible to the bluetongue virus.
The first outbreak of hemorrhagic disease was reported in a New Jersey deer herd in 1955 and claimed an estimated 700 deer. Since, outbreaks have occurred in white-tailed deer in parts of the United States and Canada, and generally occur between August and September.
Last season, Kentucky’s wildlife experts reported their worst outbreak in 30 years, and estimated several deer died in the grips of the horrible malady. In western Kentucky alone, landowners reported finding over 700 deer carcasses.
Mike Shaw a whitetail expert claims that every year Oklahoma has a few cases of hemorrhagic disease somewhere in the state. He noted that not all strains of the virus are deadly, and says some tend to actually benefit the herd by building immunities from future reoccurrences. “Oklahoma did have a very significant outbreak a few years ago,” Shaw said. “EHDV struck a southeastern county, and that particular deer season the harvest total there dropped by half. However, two years later the herd affected bounced back, and the county recorded a record harvest.”
“Unfortunately, there is nothing we can do about the virus since it is spread by insects,” Shaw surmised. He also added that hemorrhagic disease and blue tongue have no link to Chronic Wasting Disease - another malady that has affected isolated pockets of deer and elk. “EHDV and BTV are spread by a midge and CWD is caused by a protein within the animal itself,” he said.
Hemorrhagic disease seems to be more prevalent within southeastern deer herds where temperatures are generally milder and more conducive to the deadly midge populations. Biologists believe that most of the disease carrying midges die off after the first frost.
The virus attacks a deer’s blood clotting ability and causes changes in blood vessel health due to degeneration of the cells. The resulting change causes hemorrhaging in the organs and tissues throughout the animal’s body.
Evidence of the disease can go unnoticed due to infected carcasses rapidly decomposing or being eaten by predators. Deer with the disease generally exhibit typical symptoms including fever, swollen necks, tongues, and eyelids, excessive salivation, abnormal growth of hooves, lethargy, and an emaciated appearance. Some infected deer may not exhibit symptoms at all. Infected deer generally can be found near a waterhole, while some die within three days of contracting the disease. Though not all deer will die of the disease, some states have seen a decline of up to 20 percent of their herds during bad outbreaks. Surviving deer develop antibodies to the disease; however, the immunity does not guarantee that the deer will not be susceptible to future strains of a different virus.
Deer that survive hemorrhagic disease generally are marked with irregularly shaped hoofs that show sloughing and appear to exhibit re-growth. Other researchers have reported surviving deer having sores on their tongues, inside their mouths and on their cheeks. These residual maladies can affect a deer’s ability to feed and can adversely affect their overall health.
Outbreaks of the disease have been well documented in several states with Florida and Texas deer receiving the most bites by the disease carrying insects. However, recent studies have revealed that southern deer herds are now showing a greater genetic resistance to both diseases.
Ironically, pregnant does carry antibodies to the disease and pass those immunities to their fawns through their milk for their first few months. Another interesting discovery is the disease appears to be more prevalent when drought or dry conditions exist.
Though the disease mimics some symptoms of Africa’s deadly Ebola virus, hemorrhagic disease cannot be transferred to humans through venison consumption or from any contact with an infected deer, though experts suggest that any animal that appears diseased should not be eaten or handled.
Though most EHDV outbreaks are localized and not widespread, there is no known cure presently for the disease. Anyone finding a deer that appears to be diseased or a dead carcass should immediately contact a conservation officer in their area. Shaw cautioned that hunters should always wear rubber gloves when field dressing or skinning a deer for protection from parasites, and encouraged people to thoroughly cook venison before consuming it.
Read more about hemorrhagic disease