Myth: CWD is the biggest threat to whitetail deer

Last year, the Tennessee Wildlife Resource Agency and Tennessee Wildlife Federation tag teamed an all-out media blitzkrieg that warned sportsmen in the Volunteer State that CWD from farm-raised deer would wipe out the state’s entire deer herd with a massive contagion. Their media campaign frightened a lot of hunters and grabbed a lot of headlines.

But while CWD always seems to be singled out as the biggest threat to whitetail deer, the real and ever-present threat to deer herds is hemorrhagic diseases, such as Epizootic Hemorrhagic Disease (EHD) and Bluetongue.

The number of reported deer deaths due to CWD is miniscule compared to EHD and Bluetongue, both of which are acute, often fatal, viral diseases.

Hemorrhagic disease is the most important infectious disease of whitetail deer, and outbreaks occur almost every year in some areas. It is caused by either of two closely related viruses, epizootic hemorrhagic disease (EHD) virus or bluetongue virus. Because disease features produced by these viruses are indistinguishable, a general term, hemorrhagic disease, often is used when the specific virus responsible is unknown.

Unlike CWD, the EHD virus has a published track record for killing large numbers of animals. Wildlife officials in many states have documented “die-offs” attributed to EHD. The Michigan DNR, for example, reports sweeping EHD deaths in several different years — 100 deer in 1974; 50-75 animals in 2006; 150-200 deer in 2008; 300-450 deer in 2009; 1,025 deer in 2010; and 300 deer in 2011.

In total, some wildlife authorities estimate EHD kills between two- and three million deer every year.

EHD and bluetongue viruses are transmitted by biting midges, or gnats, which live in or near water and wet, muddy areas. It is transmitted to deer that congregate at such watering holes during warm, dry weather. The disease is not contagious from one animal to another, and it is not transferable to humans.

The spread of the disease is usually cut short with colder, wetter weather that spreads deer out and away from gnat-infested areas, or the first hard frost, which will kill the disease-carrying gnats. Since the incubation period for the disease is five to 10 days, afflicted deer may be observed up to a couple of weeks after frost.

Deer in the early stages of EHD may appear lethargic, disoriented, lame, or unresponsive to humans. As the disease progresses the deer may have bloody discharge from the nose, lesions or sores on the mouth, and swollen, blue tongues. They become emaciated because they stop eating. Sometimes they even stop drinking, although many die close to or in water.

Since deer hunting season usually doesn't open until well after the first killing frost, deer hunters usually don't see live, infected animals. However, hunters should avoid shooting and consuming deer that show any EHD symptoms, even though the disease cannot be transmitted to humans.

EHD typically strikes in late summer and early fall during an unusually warm, dry year when wildlife concentrates at whatever water is available.