Buckmasters Magazine

The Deadliest Disease

The Deadliest Disease

By Bob Humphrey

Despite the fear about CWD, far more whitetails succumb to EHD.

When chronic wasting disease (CWD) hit the headlines at the beginning of this decade, it was considered a significant threat. Speaking at the Northeast Fish and Wildlife Conference in April, 2002, Dr. Valeruis Geist — one of North America’s most respected big game biologists — cautioned that “if left unchecked, the disease could mean an end to huntable numbers of mule deer and possibly elk in North America within a decade, and we could even see whitetail numbers drop below huntable numbers in our lifetime.” Obviously, none of that happened. And it probably won’t.

CWD has exacted a heavy toll, although the greatest source of deer mortality has not been from the disease itself, but from state agency initiatives to significantly reduce deer populations in order to repress disease transmission. A greater cost has come in the form of the expense related to CWD programs and testing at a time when wildlife department budgets are already stretched beyond their means.

While all this was going on, whitetails were dying in far greater numbers from a diseases that has, over the last 50 years, taken a much greater toll on North America’s whitetail populations, epizootic hemorrhagic disease (EHD).

The most significant recent trouble started in 2007. “Game Commission Looking into Deer Deaths in Southwestern Pennsylvania,” read the headline of an Aug. 20 news release from the Pennsylvania Game Commission (PGC). Another followed on Aug. 27: “Test Results Confirm EHD in Greene/Washington Counties.” The disease made the headlines again on Sept. 7: “Test Results Expand EHD Infected Areas in Southwest.”

“Although difficult to determine the precise number of deer that have died from EHD, our officers’ observations and those of concerned citizens suggest the number exceeds 1,000 animals at this time and [that] could increase,” said PGC Southwest Region Director Matthew Hough.

He was right. EHD was eventually confirmed in Allegheny, Beaver, Greene, Washington and Westmoreland counties, and suspected in parts of several others. It also eventually spread over roughly two-thirds of West Virginia, as well as west and south from there.

“Reports of the disease are coming in earlier this year — and from a much wider range than usual,” came the report from the Tennessee Wildlife Resources Agency (TWRA) during that same year.

“We hear reports of EHD just about every summer, but they usually don’t start coming in until late August when hunters re-enter the woods for squirrel season, said TWRA biologist Alan Peterson. “Even then, they’re usually confined to one or two areas. This certainly seems to be something different.” It was.

TWRA officials gathered and sent tissue samples to be analyzed at the University of Georgia’s Whitehall Deer Research Facility, where biologists confirmed EHD and reported outbreaks all over the Southeastern United States. “They said it’s happening in Virginia, Alabama, North Carolina — all over the place,” Peterson said. Kentucky officials eventually documented more than 4,000 related deer deaths.

“There’s no way to put an actual number on the deer that have died as a result of EHD,” said Tina Brunjes, big game program coordinator for the Kentucky Department of Fish and Wildlife Resources.

Biologists still don’t know just how extensive or damaging the 2007 outbreak was. It encompassed parts of more than 30 states from New York to Montana and across the Southeast to Texas. It was labeled the worst outbreak in at least 50 years. The Southeastern Cooperative Wildlife Disease Study (SCWDS) received suspected or confirmed hemorrhagic disease (HD) activity from 812 counties in 31 states, approximately twice the number reported during years of moderate activity.

Eleven states (Illinois, Indiana, Kentucky, Missouri, North Carolina, Ohio, Pennsylvania, South Dakota, Tennessee, Virginia and West Virginia) estimated mortality of more than 100 deer per county. According to the Quality Deer Management Association’s 2009 Whitetail Report, the overall estimated mortality was greater than 65,000 deer. Given the difficulty in discovering deer and verifying their cause of death, mortality could easily have been much higher.

The cause of that 2007 outbreak, and a continuing threat to whitetail populations across the continent, is HD, which collectively includes epizootic hemorrhagic disease (EHD) and bluetongue. EHD and bluetongue are caused by different viruses, but both are classified as HDs.

HDs represent a far greater threat to whitetail populations than CWD. They’re infectious, viral diseases of deer and elk that are blood-borne and transmitted by biting midges or flies. The viruses themselves are always present in the wild in varying amounts, and biologists believe high deer population density is a major contributing factor to outbreaks.

It is a nasty family of diseases. As the name implies, HDs produce extensive tissue and organ bleeding, ranging in size from pinpoint to massive — the result of defective blood-clotting combined with degeneration of the blood vessel walls.

Onset is rapid, with signs occurring within about seven days of exposure. Deer initially lose their appetite and innate fear of humans and predators. As the disease progresses, they grow weaker, salivate excessively and develop rapid pulse and respiration rates. Because of the accompanying fever, affected animals are often found at or near water. Typically, deer go into shock and eventually die.

HDs occur in three forms: peracute, acute and chronic. Depending on its virulence, the peracute form can be fatal within 36 hours. The classic acute form is typically fatal within five to 10 days. The chronic form is characterized by less severe symptoms, and deer often survive. Those that do survive develop immunity, and it is believed does can pass temporary immunity to their fawns through milk.

Because EHD is transmitted by biting flies, it is seasonal. It occurs when flies are most abundant in late summer and early fall, ceasing abruptly with the onset of frost.

To date, instances of HD have been confirmed in more than 30 states. Although less common in the North, severity and associated mortality there are generally greater. Outbreaks are more common and more regular in the Southeast. However, the impact is far less in Southern deer, and some biologists believe this might be a result of higher herd immunity because of more frequent exposure.

They also cite this as a reason why transplanting big Northern bucks to the South does not work. In addition to being poorly suited to deal with Southern climates, Northern deer are not predisposed to deal with Southern disease cycles.

Predicting where and when severe outbreaks of HD might occur is not possible, and there are no effective tools for preventing or controlling them when they do. Biologists and hunters can only stand by and watch as the disease runs its course.

The good news is the effects of HDs are seldom long-lasting. Outbreaks date back to at least the 1880s, and deer populations have flourished in the aftermath.

In fact, outbreaks have been few and far between since 2007. Overall, deer herds are in pretty good shape nationwide, and keeping them that way might be the best means of prevention.

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This article was published in the October 2010 edition of Buckmasters Whitetail Magazine. Subscribe today to have Buckmasters delivered to your home.

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