Epizootic Hemorrhagic Disease Virus and Deer Loss: Wishing for a Killing Frost?

EHDV-killed deer found lying in water. (Photo courtesy of Michigan Department of Natural Resources.)

The recent appearance of groups of dead white-tailed deer in southern Wisconsin, has caused a worried and even fearful reaction for deer lovers.

Whether consciously or subconsciously, whether we hunt and use wildlife for food, or simply love the bit of nature they bring to our urban or suburban existence, many of us see wildlife as an environmental barometer.

Reports of multiple dead deer in southern WI first made the news several weeks ago. Initially the culprit was uncertain. However, we now know that Epizootic Hemorrhagic Disease Virus, an Orbivirus transmitted by Culicoides sp. (biting midges, also known as “no-see-ums”) is responsible for the deer deaths.

Not a New Disease

Epizootic Hemorrhagic Disease virus or EHD/V is not new to southern WI, but the number of deer it has killed in southern WI in 2012 is striking. The WI Department of Natural Resources (DNR) monitors reports of dead deer and the counties affected. In a late September 2012 report to the Milwaukee Journal Sentinal, the DNR’s Eric Lobner noted 178 deer deaths due to EHD.

Michigan, Illinois, Indiana and Delaware have also reported large numbers of deer deaths due to EHDV in 2012.

Increase in EHDV in Northern States: Climate Change

Interestingly, in a letter in Wisconsin Natural Resources magazine in August of 2011, the WI DNR’s Melissa Clark commented that EHD, as seen in IL, could increase in WI deer herds if climate change allowed midges to survive and move further north into Wisconsin.

EHD is not spread from animal to animal, but rather the virus is transmitted to deer and other wild ruminants, such as mule deer and antelope, by biting midges, Culicoides sp. These small flying insects are found near water, which curiously is in short supply in southern WI this summer, as we suffer one of the worst droughts in recent times.

Infected, deer develop fever, swollen and ulcerated tongues, and internal hemorrhages. Behavioral changes, such as a lack of fear of humans have been reported. Dead deer have been found congregated in and near streams, creeks and other sources of water.

The Michigan DNR website notes that EHD-infected deer may wander into water to try to cool themselves due to fever, and often are found dead, there.

Some deer survive the viral infection, and have immunity to the EHD virus. In the southern U.S. deer die-off due to EHD is less severe that what has been seen in 2012 in Michigan and Wisconsin, as the virus is more common in southern states and some deer are immune.

A Danger to Humans?

Humans in the U.S.  are generally not affected by Orbiviruses, as the  Medscape website notes:

The orbiviruses are primarily animal pathogens that cause bluetongue disease in sheep, cattle, goats, and wild ungulates; African horse sickness in horses, donkeys, and dogs; and epizootic hemorrhagic deer fever.

Note that most of the information found at this site is specific for human infections.

Can Livestock be Affected?

Livestock producers, particularly those with cattle, sheep and goats, should not find these animals affected by EHDV. These livestock animals are not believed to be susceptible to EHDV.

WI DNR officials say that deer that have died from EHD do not pose a threat to humans or dogs and that the venison is safe to eat. There is the potential, however, for deer infected with EHD to develop secondary bacterial infections and in these cases, meat should not be consumed.

How to Control the Midges

As for controlling or eradicating Culicoides sp., WI officials are looking to impending  cold weather and overnight temperatures below freezing, as the best control measure. Culicoides sp. may have ventured north into southern Wisconsin, but inhospitable freezing temperatures should soon end their stay.

For more information, see the Wildlife Health Bulletin 2012-05 on Hemorrhagic Disease in Wild Ruminants, from the National Wildlife Health Center.

While the deer loss due to EHDV is tragic, officials expect deer herds to rebound to healthy numbers.

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Kari Kenefick

Kari Kenefick

Kari has been a science writer/editor for Promega since 1996. Prior to that she enjoyed working in veterinary microbiology/immunology, and has an M.S. in Bacteriology, U of WI-Madison. Favorite topics include infectious disease, inflammation, aging, exercise, nutrition and personality traits. When not writing, she enjoys training her dogs in agility and obedience. About the practice of writing, as we say for cell-based assays, "add-mix-measure".

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