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Issues Of The Environment: Deadly EEE Virus Cause For Concern In Washtenaw County, Not Alarm

Wikipedia Media Commons

Eastern Equine Encephalitis, or EEE, is a particularly dangerous virus spread by mosquitoes.  Infections have been reported in southeast Michigan, but actions are being taken to contain the virus from spreading.  In this week's "Issues of the Environment," WEMU's David Fair talks to Juan Marquez, Medical Director for the Washtenaw County Health Department, about what's being done to fight EEE in Washtenaw County.


  • Michigan is experiencing the worst outbreak of Eastern Equine Encephalitis (EEE) in more than a decade.  Like other mosquito-borne illnesses (i.e... West Nile, Dengue, etc...), people are most likely to be infected in the late summer and early fall, because the virus has built up significantly in mosquito populations over the summer season. 

  • In humans, EEE is a mosquito-borne virus that is symptomless upwards of 95% of the population, but progresses to a flu-like illness for 5%.  Children and older adults are most susceptible to the virus. 1% of those infected develop encephalitis (brain and other neurological swelling), which commonly leads to lifelong neurological symptoms and disability.  Approximately 30% of those with encephalitic illness die. 

  • EEE can infect most animal species, but equine species (Horses, mules, donkeys, etc...) are more susceptible, and nearly 30% of infected animals die.  This year in Michigan, deer and wolves have died as well. 

  • Known cases of the virus have reached counties adjacent to Washtenaw (Jackson, Livingston), but so far no confirmed cases are detected in the county.  (That does not mean the virus isn’t here. It likely is, but perhaps no one has become ill enough to seek testing.)  In the affected counties, health departments have advised that outdoor activities be canceled and people stay indoors between dusk and dawn.  Mosquito repellents containing DEET are recommended for outdoor activities, especially in areas near freshwater, hardwood swamps, where the mosquitos that carry EEE are most common.


  • All impacted counties have undergone aerial pesticide spraying to combat spread of EEE.  The pesticides used are highly effective against mosquitos, but they also kill bees, moths, and other insects.  Spraying is done at night when most bees are in their hives.  According to the CDC, direct contact appears to be safe for other animal species and people.


  • The risk for EEE infection declines with cooler weather, and the first hard frost is believed to end the season.  It is likely that climate change plays a role in the extension of summer temperatures into the fall, which significantly increases the risk of EEE and other mosquito-borne illnesses.

  • Washtenaw County collaborates with the Tick and Mosquito Surveillance Program from the Michigan Department of Health and Human Services.  The goal of the program is to detect the species of mosquitoes that transmit Zika, Lyme disease, and other severe illnesses.

  • Juan Marquez, Medical Director for the Washtenaw County Health Department, keeps up to date will mosquito-borne infections in the county and makes recommendations for public health.  For now, the Washtenaw County Health Department advises residents to rid their properties of standing water, wear protective clothing and use DEET repellents when outdoors, and avoid activities where mosquito bites are likely.

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— David Fair is the WEMU News Director and host of Morning Edition on WEMU.  You can contact David at734.487.3363, on twitter @DavidFairWEMU, or email him at dfair@emich.edu

Contact David: dfair@emich.edu
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