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Virus a silent killer of North Dakota deer herd

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DEER DILEMMA: There have been more than 70 reports this fall of dead deer whose deaths were found to be consistent with epizootic hemorrhagic disease virus.
Pronghorns, mule deer and even cattle herds show limited infection rates.

North Dakota deer hunters had a successful season, but there was another predator adding to this fall’s deer kill.

Epizootic hemorrhagic disease virus is laying claim to a high number of deer this year, “just as bad as 2011,” according to Charlie Bahnson, wildlife veterinarian with the North Dakota Game and Fish Department.

EHD is a virus that, as the name implies, causes hemorrhagic disease, and primarily affects white-tailed deer. It has also been found in mule deer and pronghorn antelope, as well as some of North Dakota’s beef cattle.

Some EHDV occurs in North Dakota most years, but the NDGFD typically only receive a handful of reports. This year, early hunting season reports found “well over 70 reports of dead deer that were consistent with EHD,” according to Bahnson. It prompted the NDGFD to solicit reports from hunters. He clarifies that a “report” could include one or 10 to a dozen dead deer, and admits that many fallen deer may not be discovered.

Compared to 2011, a historically bad year for EHDV, Bahnson says a couple of trends developed as far as regions of the state affected. The region south of Interstate 94 and west of the Missouri River is the EHDV “epicenter,” but it appears “the real far southwest was not heavily involved this year,” he notes. “What was interesting is, we had positive detections and reports in a number of areas east of the river, which is pretty atypical.” The furthest confirmed EHDV case this year was in Sargent County in the southeast part of the state, bordering South Dakota.

Not just white-tailed deer

Bahnson says the “poster child” for EHDV infection would be the white-tailed deer, but “we did have positive detections in pronghorn scattered across the region, as well as mule deer, and even in elk down in Sioux County” in the south central part of the state, bordering South Dakota.

In early November, South Dakota Game, Fish and Parks offered hunters in Aurora, Faulk, Hand, Hughes, Hyde, Jerauld, Potter and Sully counties the opportunity to voluntarily return their East River deer tags due to an EHDV outbreak.

Bahnson says hunters in the heavily impacted areas in North Dakota were also offered refunds, “but typically, not a lot of hunters take us up on that offer. They still choose to go hunting.” Early surveys indicate a high hunting success rate across the state.

Another anomaly with EHDV in North Dakota this year was that the disease, spread by a biting midge, is usually seen in late-summer or early fall. “We had a couple hard freezes around Sept. 10, and we were hoping that that would slow or stop things, but it really didn’t.,” Bahnson says. “We continue to get reports of freshly dead deer and even had a positive PCR [polymerase chain reaction] result as recently as Nov. 2. For a variety of reasons, it ended up being a bad year.”

Bahnson stresses that EHDV is not transmissible to humans, and it is not harmful to eat venison from a hunted deer that has been infected with the virus.

Impact on cattle

It is believed that more deer mortalities are reported because white-tailed deer are more sensitive to the virus compared with pronghorns, mule deer and even beef cattle.

“It is not uncommon to see those high numbers affected, especially in whitetail, and a significant number of those die,” says Beth Carlson, deputy state veterinarian with the North Dakota State Board of Animal Health. “Whereas with cattle, it’s typically a small number of animals affected, and a really small percentage of those die.”

According to a fact sheet from The Center for Food Security & Public Health at Iowa State University, “Clinical cases are generally less severe in cattle than in white-tailed deer, and most animals recover. Reported overall mortality rates up to 2% [in cattle].” According to the CFSPH fact sheet, wild deer mortality rates were estimated to be 6% to 20% during some outbreaks.

Carlson adds that there is a small amount of federal dollars available to assist beef producers with laboratory costs associated with a case of unusual mortality, “with multiple animals affected where there’s not a typical suspected cause; and since they’ve already experienced a financial loss, that’s sometimes helpful to inspire producers to submit samples in an unusual case.”

Carlson encourages producers with suspect animals to alert their herd veterinarian to investigate, because some of these diseases can present similarly to foreign animal diseases, such as foot-and-mouth disease. Veterinarians also need to contact the Animal Health Division of the North Dakota Department of Agriculture to request use of these federal dollars on behalf of the producer, as there is a formal procedure that needs to be followed.

“They may not want to pursue diagnostic testing because they’re not seeing a significant loss or significant number of animals,” Carlson says. “They’re seeing one or two animals that are off, and it might not even occur to them that they’re dealing with a contagious disease.”

Bright future?

“The fortunate thing is that in white-tailed deer, viremia is extremely brief,” Bahnson says. “It’s generally, on average, less than 10 days. So we don’t really see a meaningful effect and actually, what’s a bit encouraging is, we know that there’s a pretty strong, protective effect in maternal antibodies in the following year.”

He believes that it would be rare to find a deer that didn’t have some level of exposure this year. “And that’s actually kind of a good thing. It operates the same way as a vaccine, so knock on wood, we should be relatively protected at least for another year or two from kind of bad years, and in this particular area of the state.”

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