Hundreds of deer fall to Iowa’s most widespread outbreak of epizootic hemorrhagic disease

The most widespread and third-most severe outbreak on record of a disease transmitted by biting flies is plaguing Iowa deer this fall.

Epizootic hemorrhagic disease, or EHD, is a viral disease spread to deer by biting flies called midges or no-see-ums. The disease has been in the southeastern and northeastern United States for decades, and was first discovered in Iowa in 2012. It’s often but not always fatal. It cannot infect humans.

The Iowa Department of Natural Resources has received 1,074 reports of suspected EHD-related deer deaths so far this year, said state deer biologist Jace Elliott. Actual mortality may be even higher considering unreported deaths.

Death reports span 68 of Iowa’s 99 counties, making it the most widespread annual distribution on record.

Reports are most concentrated in Southeast Iowa around Henry and Van Buren counties, which each have more than 100 reports. Clayton County in Northeast Iowa has topped 100 reports as well. Counties with the most reports typically also have larger deer populations. The vast majority of counties are seeing less than 10 reports each.

“Since over half the state has at least one suspected mortality, this is very much more widespread than we typically see,” Elliott said. “But the vast majority of the counties affected are experiencing very mild outbreaks.”

Iowa typically sees about 50 reported cases of EHD each year, spanning between 10 to 15 counties.

The worst outbreak on record in Iowa occurred in 2012 — EHD’s first appearance in the state — when the Iowa DNR received 2,974 reports of suspected EHD-related deaths. The second-worst outbreak occurred in 2019 with at least 1,800 deer deaths.

“It is a fairly new disease. That means that our deer are fairly susceptible and have a relatively naive immune response,” Elliot said. “I think that that's going to change over time. … The deer that end up surviving the disease go on to produce offspring that are more resistant to the disease.”

Because of the disease, landowners could find several dead deer on their properties. Dead deer should be reported to the Iowa DNR, conservation officers or local wildlife management staff. But the disease shouldn’t cause major impacts to overall deer populations in Iowa unless there are sustained outbreaks year-over-year. That hasn’t been the case in the state so far.

This year’s outbreak shouldn’t impact the deer hunting season, Elliott said. Iowa’s early archery hunting season already is in progress. Shotgun season spans early- to mid-December. Late muzzleloader and non-resident holiday seasons come later in December. The National Deer Association says humans are not at risk by handling EHD-infected deer or eating the venison.

EHD is seasonal, peaking in the late summer and early fall. Hard frosts kill the midges. This year’s warmer fall prolonged the lives of the infectious midges and may have contributed to the outbreak, giving extra opportunities for the disease to spread.

The first hard freeze is expected to hit Iowa by early next week, according to the National Weather Service Quad Cities bureau.

“We certainly expect that this disease activity is more or less done for the year,” Elliott said.

On the other hand, another disease still is ramping up among Iowa’s deer populations: chronic wasting disease. It is caused by misfolded proteins in the brain called prions that damage the brain and eventually kill the infected animal. The proteins are shed through bodily fluids and can spread through direct contact or environmental contamination. The disease has a 100-percent mortality rate.

Chronic wasting disease is increasing in prevalence and geographic distribution in Iowa since its first detection in 2013, Elliott said. Since then, 261 deer have tested positive for the disease. Ninety-six of those positive results came last year. Two deer have already tested positive this year — one in Marshall County, the other in Jackson County.

“We're hitting an exponential rise in disease prevalence, particularly in Northeast and South-Central Iowa,” Elliott said.

To date, there have been no reported cases of chronic wasting infection in humans, according to the Centers for Disease Control and Prevention. But hunters should not eat meat from deer that have tested positive for the disease. Hunters can contact their local Iowa DNR wildlife management staff for deer testing.

Brittney J. Miller is the Energy & Environment Reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

Comments: (319) 398-8370; brittney.miller@thegazette.com