More than 700 white-tailed deer have been reported dead in one Wisconsin county this summer, part of a growing outbreak that wildlife officials believe is being driven by a virus spread by tiny biting insects.
The Wisconsin Department of Natural Resources says the reports, which began in July and were initially concentrated in Washington County, now include Waukesha and Ozaukee counties. As of Sept. 3, the agency had received more than 700 reports in Washington County, more than 150 in Waukesha County and just over 30 in Ozaukee County.
The disease is called epizootic hemorrhagic disease, or EHD. It can spread quickly through deer populations during late summer and fall, when the insects that carry the virus are most active.
Here's what to know
about the outbreak and the disease behind it.
What's killing the deer?
EHD is a viral disease that affects white-tailed deer and other hoofed animals. It is spread by biting midges, tiny insects sometimes called "no-see-ums."
In severe cases, the virus can cause a high fever, internal bleeding and organ damage. Infected deer may become weak, salivate heavily or develop foam around their noses.
Because of the fever and dehydration, sick deer often seek water. Wildlife officials have found many dead deer in or near ponds and other water sources during outbreaks.
The Wisconsin DNR tested two deer from Washington County and found both were positive for EHD. The agency has continued tracking reports of dead deer in the surrounding counties but does not plan to test additional deer within the area of the known outbreak unless reports come from farther away.
Why can EHD be so deadly?
EHD is less common in Wisconsin than in Southern and Western states, and Wisconsin deer have not historically been exposed to the virus as regularly as deer in areas where it is more common.
The DNR says death rates can be higher in places where hemorrhagic disease is rare. Deer herds with high population densities also can experience greater mortality.
Wisconsin first confirmed EHD in 2002. The state has seen sporadic outbreaks since then, including one in 2012 that was reported across eight counties.
The state is also near the northern edge of the range for the insects that spread the disease. The DNR says warmer temperatures could allow those insects to expand farther north, potentially creating conditions for more outbreaks.
What happens to deer that survive?
Not every deer infected with EHD dies. Survivors can develop antibodies that may help them withstand future outbreaks.
Outbreaks also tend to be temporary. The disease usually fades after the first hard frost, which kills the midges that transmit the virus.
Is EHD the same as chronic wasting disease?
No. EHD is caused by a virus and is transmitted by biting insects. Chronic wasting disease, or CWD, is caused by abnormal proteins called prions and spreads through infected animals and contaminated environments.
The two diseases also progress differently. EHD can cause severe illness and death relatively quickly, while CWD develops much more slowly and is fatal in infected deer.
Can EHD infect people?
No. The Wisconsin DNR says the viruses that cause hemorrhagic disease do not infect humans. People are not at risk from handling an infected deer, eating venison from an infected deer or being bitten by a midge carrying the virus.
The DNR is asking residents to report unusual numbers of sick or dead deer so wildlife officials can continue monitoring the outbreak.
Contributing: Milwaukee Journal Sentinel reporter Paul A. Smith
Reporter Anthony Thompson can be reached at ajthompson@usatodayco.com or on X @athompsonUSAT.
This article originally appeared on USA TODAY: What's killing hundreds of deer? Here's what to know.
