Buckmasters Magazine

Should We Fear EHD?

Should We Fear EHD?

By David Hart

Outbreaks seem to be more frequent and devastating.

Around mid-November last year, social media sites started buzzing about what seemed like a sudden decline in Virginia’s deer population. Some members of the hunting community dismissed the claims as a result of the bumper crop of acorns. After all, when mast is abundant, the deer harvest declines. But something was different. Even hunters who use dogs to run deer were seeing fewer whitetails. They were, however, seeing more and more dead deer as the season progressed.

It turned out much of Virginia was in the midst of an outbreak of epizootic hemorrhagic disease, or EHD. Although not confirmed, some hunt clubs reported dozens of carcasses along creek beds and around ponds, a telltale sign of the disease. What was obvious, though, based on anecdotes and reports on social media sites, is that many hunters in central and southern Virginia found at least a few dead deer. Their suspicions were correct.

“It was the worst outbreak I’ve seen in the 25 years I’ve been working here,” says Virginia Department of Game and Inland Fisheries deer project coordinator Matt Knox.

Although it’s impossible to put a number on the severity of the outbreak, statewide harvest statistics paint a telling picture. Deer kills were down by more than 40 percent from the previous season in many counties.


Hemorrhagic disease, also known as blue-tongue (the diseases are different, but so similar the names are often used interchangeably), is an endemic disease that has been part of the landscape for as long as there have been white-tailed deer.

It is most common in the South and Southeast, but outbreaks have occurred in nearly every state in the Lower 48. It mostly affects whitetails, but hemorrhagic disease has also stricken everything from mule deer and elk to antelope and bighorn sheep.

No species, however, suffers as heavy a toll as whitetails. That’s largely because there are more of them, although scientists aren’t exactly sure why whitetails are more prone to the disease in places they interact with other members of the deer family.

Outbreaks tend to take place in dry years, presumably because limited water sources force deer to congregate around available water. The disease is spread by tiny flies called midges, which breed and live near water, as well. The flies don’t actually harbor EHD. They simply transfer it from one infected deer to another through bites.

Also known as sand fleas or no-see-ums, these little bugs are the same ones that bite humans. However, we don’t get hemorrhagic disease.

EHD isn’t always fatal for deer, but it certainly makes them miserable. The head, neck and tongue can swell, and they lose their appetite and become feverish. One obvious sign is hoof sloughing or deformities. Hoof growth is interrupted, and the outer hooves can either fall off or become deformed.

Hemorrhagic disease also causes a significant fever and dehydration, which is why dead or dying deer are found in or near water.


In places EHD is most common, a large portion of infected deer survive. In fact, once infected, they develop an immunity. They carry the disease but never show symptoms. That’s why significant, or acute, outbreaks are relatively rare in the South and Southeast. Because the disease is so prevalent, many of the deer are carrying EHD, but it has no noticeable effect on them.

However, that level of immunity can diminish as animals with an immunity die and no outbreaks occur within the next generation. As a result, outbreaks can increase in severity when they do occur since fewer deer are immune.

Even in places with large EHD-related deer kills, outbreaks tend to be very localized, says Iowa Department of Natural Resources deer project leader Willie Suchy. He says hunters or landowners on one farm might find a dozen or more dead deer, while there might be no deaths attributed to the disease a few miles away.

“We examined harvest figures following years with significant EHD deaths and found overall harvest numbers on a county-by-county basis were virtually unchanged from years without EHD outbreaks,” Suchy said.


The bad news? Outbreaks might be getting more severe and more frequent. There’s no better evidence than what took place in parts of Montana and the Dakotas in 2011 and 2013.

North Dakota Game and Fish veterinarian Dr. Dan Grove examined historic outbreaks over the past 60 years and found there were outbreaks about every seven years until the early 2000s. Then, outbreaks became more common and more severe.

“We had three significant outbreaks and one minor one in the past seven years alone,” says Grove. “That indicates we are seeing a higher rate of outbreaks.”

There were two significant events in Iowa. Suchy said deer deaths were severe in 2012 and 2013. Prior to that, the only back-to-back outbreaks took place in 1987 and 1988, although those weren’t as severe as the most recent ones.

“Normally, we see EHD outbreaks every 10 or 15 years,” he said.

Although some scientists suggest the increase is related to climate change, Grove says there are a number of factors at play. First, much of the Great Plains is seeing a significant loss of suitable deer habitat. The Dakotas, Nebraska, Kansas and parts of Montana have seen a marked decline in land enrolled in the Conservation Reserve Program, which typically consists of native grassland. It’s high-quality bedding and fawning cover. Shelter belts (rows of trees planted to prevent wind erosion) also are being knocked over to make room for more crops. That forces whitetails into the remaining habitat, effectively crowding more deer into less space.

“When they are grouped into smaller areas, it’s easier for the disease to spread from one deer to another,” Grove said.

However, the disease is also thought to be linked to severe weather.

“When we think of climate change, we typically think of it as a warming trend, but that doesn’t seem to be the case,” says University of Georgia veterinary professor Dr. David Stallknecht, who specializes in wildlife diseases. “Climate change is linked to more extreme weather on both ends of the spectrum. It makes sense that the increase in severity of outbreaks and the increase in numbers of outbreaks north of the Tennessee/Georgia line would be related to a long-term warming trend, but we don’t have any hard data that supports that.”

Suchy says a number of models show more droughts in the future, which would lead to more EHD outbreaks and possibly more severe outbreaks in northern states. While drought conditions often are blamed for EHD outbreaks, it’s the entire weather cycle that leads to more severe occurrences. North Dakota was exceptionally wet in the spring of 2011 and 2013. The summer and fall were relatively dry years. Abundant water translates to lots of mud, which is where biting midges thrive. As that water disappears, deer and the flies that carry EHD are forced into smaller areas.

The increase in outbreaks isn’t necessarily devastating to populations in the long run. They can usually rebuild their numbers in two or three years. However, as Grove notes, when major outbreaks occur every two or three years, it can have a major impact on long-term population trends. Just as the deer rebuild, they might get knocked down again.

What scientists don’t know, Stallknecht said, is how EHD impacts older deer, particularly in areas where hunters use trigger restraint to manage for older age classes. So far, there are no studies that have examined how the disease impacts more mature deer.

Nor is there a consensus on how large-scale population densities affect the spread and severity of disease outbreaks. At one time, biologists thought there would be larger and more widespread outbreaks as deer numbers in a given area increased, but Stallknecht said there is no evidence that supports that outbreaks are related to population density.

While there are still many unknowns related to hemorrhagic disease, there’s no question recent outbreaks have had a significant impact on deer herds and the hunting opportunities tied to them.

Many Virginia hunters simply quit hunting mid-season after seeing few or no deer where they would normally see several.

A 2011 outbreak in Montana killed upwards of 90 percent of the whitetails along the famed Milk River. A large number of pronghorn antelope also died from EHD.

As a result, Montana Fish, Wildlife and Parks cut deer tags by 60 percent in eastern Montana. North Dakota officials suspended 1,500 deer tags and offered refunds for them in, also in 2011. Meanwhile, disease outbreaks combined with severe winters continue to depress deer numbers in some regions.

Is this the new normal? It’s a tough call, Stallknecht said, but if trends continue, hemorrhagic disease could show up in deer herds where it has never caused problems in the past.

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This article was published in the July 2015 edition of Buckmasters Whitetail Magazine. Subscribe today to have Buckmasters delivered to your home.

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