Epizootic hemorrhagic disease, a midge-borne virus that is every bit as nasty as its name suggests, had an unusually lethal impact on South Dakota's deer herd this year.
It was a record-setting year, in fact, although not one that hunters or the state Game, Fish & Parks Department are celebrating.
GF&P officials estimate that at least 3,400 deer died of EHD in 2012. That's more than twice the 1,300 reported in 2011, which was the previous high in reported EHD losses in South Dakota.
And both numbers were likely conservative, since some deer killed by the disease, which is spread by small biting flies, likely weren't found while others were probably noted but not reported.
Whatever the total, the losses were high enough to cause several thousand deer tags to be returned or withdrawn prior to hunting seasons in areas where EHD hit especially hard and deer numbers were noticeably reduced.
"We offered a refund before the season to any deer hunter East River or West River who felt their deer hunt wasn't going to be as good because of the disease," said Andy Lindbloom, a senior big-game biologist with GF&P in Pierre. "And there were definitely landowners who didn't want people hunting this year, so those folks had a chance for a refund."
In all, about 2,600 licenses totaling 4,300 tags — some licenses allow the taking of more than one deer — were returned at hunter requests, Lindbloom said. And GF&P withdrew another 560 licenses and 1,160 tags for the West River rifle deer season and 1,060 licenses and 1,270 tags for the East River rifle season.
GF&P began getting reports of the die-off in August as deer — primarily whitetails — began showing up near and in creeks, rivers, lakes and wetlands. Infected animals typically seek water and shade when the fever and other EHD symptoms hit, GF&P wildlife biologist Steve Griffin of Rapid City said.
"They're trying to combat the fever, so they'll go to those areas trying to get cool," he said. "They'll actually be lying in streams. I got one near Oral that was lying in an irrigation ditch. It tested positive."
GF&P had enough deer tested across the state to confirm the disease, then presumed many others died of EHD because of similar behaviors and carcass locations. EHD shows up in varying degrees every year in South Dakota, typically in scattered locations and without widespread deer deaths.
"We have minimal losses probably every year in some parts of the state. Normally, we see it in late summer, early fall," Lindbloom said. "The primary vector of the virus is a biting midge, and once we get cooler weather and a frost, that vector pretty much disappears."
EHD can also infect livestock, although the effects are typically not as severe as with white-tailed deer. It is not considered a health threat to humans.
By early September, it was clear the EHD problem was going well beyond typical losses and was also more widespread than usual.
"By mid-August we started getting reports, and the last two weeks of August and the first two weeks of September was a very busy, busy time," Griffin said.
Some areas were hard hit by the disease while others seemed hardly affected at all. That is typical, since localized outbreaks tend to depend on whether conditions are right for the midge that causes the disease. Eastern South Dakota has been spared widespread EHD losses until this year.
"Usually the environmental conditions aren't right over east. We have enough water, keep the wetlands pretty full, get the system flushed with rains," Lindbloom said. "Out west, you get the low water levels, stagnant situations, mud flats; it's all good for the mid hatch."
West of the Missouri River, Meade, Lawrence, Butte and Gregory counties had areas of significant EHD losses, as did parts of Bennett County. An area along the Redwater River northwest of Spearfish was an example of how hard the disease hit in certain areas.
"We got a report from somebody who canoed the Redwater River and saw 10 or 11 deer floating," Griffin said. "It really hit hard along in there."
In other instances, ranchers who knew their property well would call and report total die-offs that sometimes totaled dozens of deer on a ranch, Griffin said.
EHD is a common cause for typically small, localized losses in western and central South Dakota. But this year it hit particularly hard in southeast South Dakota, sharply reducing some deer herds in southeast counties along the Missouri River.
The Black Hills themselves were spared significant losses, in large part because the midges don't do well at higher elevations, Griffin said. This year, which was warmer and drier, there were some EHD reports in the Hills but not at very high elevations, he said.
"It's an elevation thing," he said. "We just don't get the number of midges up in the hills."
Griffin and Lindbloom are both hoping for reduced EHD losses in 2013. Different conditions, including improved moisture, could help. But resistance to the disease in those deer that survived this year could be especially important.
"The general belief is that the deer surviving this year will have some resistance to the disease next year," Lindbloom said. "We're hoping that in many of those areas the results won't be the same."