Drought Brings Deadly Deer Virus to Chicago for the First Time

Photo of an EHD-infected deer in Poplar Creek, via the Chicago Tribune.

It sounds like something from a horror film. Thousands of diseased white-tailed deer carcasses are cropping up across the Upper Midwest. Typically, the virus responsible only affects deer in the Southeast, but this summer's relentless drought may be responsible for the outbreaks in Indiana, Michigan, and now Northern Illinois, at least 100 confirmed cases in Cook County alone, and still others in nearby Kane County.

The disease is spread by tiny insects called midges, sand flies, or no-see-ums. Female midges are known to suck blood from host animals, thereby spreading a deadly orbivirus called Epizootic Hemorrhagic Disease (EHD). Outbreaks occur in the Southeast almost every summer, but it has never spread this far north to Chicago.

"This is the first time it's ever occurred here," confirms local wildlife expert Chris Anchors of the Forest Preserve District of Cook County. Some deer deteriorate rapidly, with severe internal bleeding in the face, neck, and lungs, causing death in just 1 to 3 days. Others may suffer through the symptoms for weeks or even months, slowing becoming emaciated and immobile.

Biologists believe that current drought conditions in the Midwest are to blame for such an unprecedented northern outbreak. Low rainfall forces white-tailed deer to drink from a limited number of water sources where midges thrive.

The only good news is that the disease cannot be transmitted to humans, or even livestock, and that Chicagoland's first overnight freeze will kill all of the disease vectors (the insects; infected deer can't transmit EHD to uninfected deer through contact).

If you can stomach it, here is a video of a deer suffering from EHD in Indiana. If you spot a deer displaying this behavior, or a carcass with lesions, please call your local Forest Preserve District.

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