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Viewpoint: How should wildlife officials look at EHD?

While many have predicted over the years that CWD might harm deer herds, it’s actually EHD that has had a greater impact on deer and hunting opportunities.

Charly_Seale.jpg
Charly Seale
Contributed / American Cervid Alliance
We are part of The Trust Project.

This fall, a hunter’s nightmare came true. An outbreak of disease was so bad in North Dakota that the state began refunding up to 30,000 deer tags.

You can be forgiven if your first thought jumped to Chronic Wasting Disease, a much talked-about deer disease the DNR has been aggressively tracking in Minnesota. This wasn’t CWD. It’s EHD, short for Epizootic Hemorrhagic Disease.

While many have predicted over the years that CWD might harm deer herds, it’s actually EHD that has had a greater impact on deer and hunting opportunities.

In Iowa, the state reports detecting 112 cases of Chronic Wasting Disease–ever. In contrast, in 2019 alone more than 1,800 deer died from Epizootic Hemorrhagic Disease.

In Missouri, the contrast is starker. The state Department of Conservation reports 206 total cases of CWD after about a decade of testing. Yet in 2012 alone, there were over 10,000 cases of EHD.

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The worst may be Nebraska. In 2019, the most recent year available, the state detected 168 cases of CWD in deer. Yet in 2012, EHD contributed to the death of an estimated 30 percent to one-half of deer in the state–perhaps 50,000 animals or more.

For all of the press CWD gets, wildlife officials really ought to be focused on EHD. To understand why, let’s consider what we know about the two.

EHD isn’t constant. It flares up in some years, particularly with a drought. When it does, it kills within days and can devastate local populations.

CWD, in contrast, has an incubation period that can last over a year. (Some CWD-positive animals in Norway were over 15 years old.) While CWD may be “invariably” fatal if an animal is in a zoo, CWD’s real mortality rate is lower than that because deer may die of something else–starvation, predation, vehicles, other diseases – long before CWD would kill them.

These details are part of the reason the evidence hasn’t borne out the most dire predictions that CWD would devastate hunting.

CWD was first detected in free-ranging deer 40 years ago in Colorado. If it was as viral and deadly as the doomsayers said, then we’d have seen those predictions become reality by now.

Yet, four decades years later, hunting is still going strong in Colorado. (Thankfully.)

The same is true in Nebraska, which first detected CWD 20 years ago. Harvests generally increased steadily in the 00s. Even after the EHD decimation of 2012, deer populations are rebounding fairly quickly.

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Which brings us to the meat of the matter: What can be done about EHD?

Not much. But that may be OK in the end.

Like any disease, it exists out in the wild. EHD is carried and spread by midges that thrive in still water and mud. Good luck getting rid of watering holes across the country. Nor can we control whether there’s a drought in any given year, much as farmers wish we could.

Similarly, we can’t stop deer with CWD from walking from one state to another – which is how it has slowly spread from Colorado to other states over several decades. Researchers also believe it can occur spontaneously. (Most humans who get Creutzfeldt-Jakob Disease, a rare cousin of CWD, get it spontaneously.)

Nature adapts. Deer in the South have begun to develop some resistance to EHD, because they encounter the virus more frequently. Deer in the North don’t have this resistance, which is why EHD hits particularly hard in those areas. For now, at least.

Similarly, there’s evidence that certain deer genes can provide a resistance to CWD. Over time, resistance will become more common through natural selection (or, on farms and research facilities, through selective breeding).

EHD, CWD, and numerous other deer diseases have been around for decades. They don’t affect people. And ultimately, they don’t seem to affect hunting opportunities in the big picture. That’s something we can all be thankful for.

Charly Seale is the Media Review Committee chairman for the American Cervid Alliance, an organization comprised of 41 separate elk, deer and exotic associations.

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