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The Bite That Kills - EHD

Article By 
Ron Wilson
Deer with EHD
 

Scientists understand that white-tailed deer in North Dakota die every summer from epizootic hemorrhagic disease, because the biting midge responsible for transmitting the virus is forever present.

It’s just that some years more whitetails are killed from the disease than others, and 2013 happens to be an outbreak year.

In mid-September, Dr. Dan Grove, North Dakota Game and Fish Department wildlife veterinarian, said it was impossible to say exactly how many deer had died up to that point.

“We can only get an estimate based on the phone calls of dead deer, frequency and location,” Grove said. “We went out and looked at one last week where the landowner reported 30 dead deer. We were shown 10 deer that were easy to get to, so the thinking is that there were more on the property.”

With reports of dead whitetails from Bowman to Bismarck, and the likelihood of more to follow, Game and Fish Department officials decided not to issue about 1,000 doe licenses remaining after the second lottery in three hunting units in southwestern North Dakota.

Randy Kreil, Department wildlife division chief, said the decision was based on previous years’ experience where moderate to significant white-tailed deer losses were documented in situations similar to 2013.

While Grove said in mid-September that it was difficult to characterize this year’s EHD outbreak as it was still ongoing, he did say it likely isn’t as bad as 2011 when dead deer were reported from southwestern North Dakota to the Canadian border and as far east as Minot.

EHD Lifecycle Diagram

Typically, EHD is something that mainly occurs in the southwestern part of the state. “Unlike 2011, we haven’t had any reports north of Interstate 94. But the experts say the disease will go as far as the wind will blow the midge,” said Grove, who noted that there were two confirmed EHD cases in the Grand Forks area in 2006.

According to the Southeastern Cooperative Wildlife Disease Study, the leader in hemorrhagic disease research in the country, EHD is the most important viral disease of white-tailed deer in the United States.

“It causes the most losses of white-tailed deer in the United States,” Grove said. “Hemorrhagic disease kills deer more efficiently than other factors, such as chronic wasting disease, starvation during difficult winters, habitat loss … you name it.”

 

The naturally occurring disease, as it’s been said before, is spread by a biting fly, or midge, that some people refer to as no-see-ums. EHD is primarily a disease of ruminants, or cud-chewing animals with four stomach chambers, such as white-tailed deer, mule deer, pronghorn, bighorn sheep, moose, elk, bison, cattle and domestic sheep. While all these animals can be infected with the virus, it seldom kills anything but whitetails in North Dakota. However, Grove said, the Department received unconfirmed reports of deaths due to EHD to pronghorn and mule deer in 2013.

“We don’t know why mule deer, elk, moose, pronghorn and bighorn sheep don’t die from the disease,” Grove said. “Researchers say these animals are all susceptible to the disease, but just not on the same level as whitetails.”

Killer Bite

While it makes sense that EHD has been killing white-tailed deer in the state for years and years, it wasn’t until 1962 that the disease was first identified in North Dakota as the culprit to a whitetail die-off.

Over the years, North Dakota OUTDOORS has covered news of EHD outbreaks and how they happened. The following, which came on the heels of an outbreak in the mid-1990s, is an example.

Deer Dead From EHD

EHD starts innocently enough, with a female midge biting an animal that hosts an active virus. When an outbreak is underway, several ruminant species can carry the virus, but in the beginning the midge needs to bite something that is still carrying the virus, which is called a reservoir host.

The primary reservoir host – the animal from which EHD begins – has been identified as domestic cattle. Some cattle – not all of them harbor the virus – can host active EHD virus for up to 8-10 months, allowing the virus to overwinter in North Dakota.

 

While the EHD virus lives in some domestic cattle, it rarely affects them. But when a female midge bites a cow that carries a virus, in an attempt to secure a blood meal to nourish her eggs, the virus can transfer with the blood to the midge. After an incubation period of 10-14 days, the virus has multiplied in the midge to a point where it can be transferred to another animal.

By the time the midge needs a blood meal to nurture a second or third crop of eggs, it can transfer the virus to the next animal it bites. If that animal is another cow, sheep, mule deer, pronghorn or any other warm-blooded animal, the virus is transferred but fought off by the animal’s immune system. However, this new blood donor becomes a host for the virus.

Grove said white-tailed deer infected with the disease in North Dakota almost always die, and they do so within three to four days of showing clinical signs. During the early stages of the disease, these deer are also important virus hosts, perhaps the most important hosts once the disease gets rolling.

“The virus, depending on weather and other factors, dies within a couple of hours after the animal dies,” Grove said. “Dead animals aren’t at risk of spreading the disease. That’s why the midge plays such a critical role.”

The more animals that become part of the cycle, the greater the odds that a midge carrying the virus will bite a whitetail. When habitat and weather conditions are right, midge populations can explode, further increasing the odds.

Grove said whitetails with EHD often die in water or are found near water. “An infected whitetail will seek out water because it’s running a fever,” he said.

Before dying, a whitetail may wander, walk in circles, or simply act as if it doesn’t know what it’s doing. The clinical abbreviation for this, Grove said, is ADR, which stands for “ain’t doing right.” A deer that “ain’t doing right” is going to die, he said.

Some postmortem signs of death by EHD, Grove said, include bloody froth from the nose and anus, and pink skin caused by fever.

According to the Southeastern Cooperative Wildlife Disease Study, there are no wildlife management tools or strategies available to prevent or control hemorrhagic disease in wild animals. While EHD is not infectious to humans, a large number of dead animals on the landscape can cause alarm and the only thing to do is hope for a change in the weather.

“You need a hard freeze to kill the midge,” Grove said. “Some years we might not see that first hard freeze until late October, which means the disease simply hangs on that much longer.”

RON WILSON is editor of North Dakota OUTDOORS.

(Editor’s note: Winter arrived, if only temporarily, in southwestern North Dakota October 4-5. Snow and below freezing temperatures, a Game and Fish Department wildlife biologist said, will be helpful in limiting the continuation of the EHD outbreak in the area.)

EHD Outbreaks in North Dakota:

  • 1962
  • 1970
  • 1971
  • 1976
  • 1981
  • 1987
  • 1988
  • 1995
  • 2000
  • 2003
  • 2008
  • 2011
  • 2013

(Note: In 1994 a small outbreak was isolated in the Yellowstone River bottoms southwest of Williston, but it was not particularly significant in terms of geographic area or number of deer deaths. According to Game and Fish Department records, the outbreak in 2000 was not widespread.)