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The original item was published from 10/28/2019 12:41:00 PM to 11/2/2019 12:00:04 AM.

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Posted on: September 26, 2019

[ARCHIVED] Eastern Equine Encephalitis (EEE) Information

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Update on EEE and aerial spraying in Washtenaw County

As of Oct 8, 2019, Washtenaw County has no human or animal cases of EEE. We still strongly encourage preventing mosquito bites whenever possible.

Washtenaw County Health Department has agreed to participate in the recommended aerial spraying in a small portion of northern Washtenaw County to combat spread of the potentially deadly EEE virus. The area targeted for spraying is a 2.5 mile radius around the confirmed animal case in neighboring Livingston County. This area includes parts of Livingston County, as well as northern Northfield and Webster Townships in Washtenaw County. This decision was made in collaboration with the Michigan Department of Health and Human Services (MDHHS); an aerial spray will lower the mosquito population and reduce the risk of humans or animals contracting EEE. 

All planned aerial spraying in Michigan has been completed. The small portion of Webster and Northfield Townships in northern Washtenaw County was completed the night of Oct 5.  Please see for updates and maps. map detailed county spray

To date, EEE has been confirmed in ten people in Michigan, with four fatalities, in Barry, Berrien, Calhoun, Cass, Kalamazoo and Van Buren counties. In addition, cases have occurred in 39 animals from 16 counties: Allegan, Barry, Berrien, Calhoun, Cass, Genesee, Jackson, Kalamazoo, Kent, Lapeer, Livingston, Montcalm, Newaygo, St. Joseph, Tuscola and Van Buren.

Residents were able to opt out of the recommended spraying intervention. Opting out is now closed because all planned aerial treatment has been completed.

What is Eastern Equine Encephalitis (EEE)?

EEE is a rare disease caused by a virus that is spread by infected mosquitoes. EEE virus is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain (encephalitis). In the United States, approximately 5-10 EEE cases are reported annually. Unfortunately, multiple human and animal cases have been reported in Michigan this year. Even with the unexpected number of cases in Michigan this year, EEE infection is considered rare. As of Oct 8, no human or animal cases of EEE have been identified in Washtenaw County. 

Symptoms usually occur within 4-10 days after the infected mosquito bite. Symptoms can be severe, including sudden onset of high fever, headache, and stiff neck. EEE can cause swelling of the brain, leading to seizures, coma, or death.

The mosquitoes that can carry the EEE virus are most often found in and around hardwood forests or freshwater swamps and bogs, usually at night between dusk and dawn. Not all mosquitoes can carry the EEE virus, and only about 4-5% of human infections result in EEE illness. Individuals who are over the age of 50, under the age of 15, or have compromised immune systems due to underlying medical conditions or treatments are at elevated risk for contracting the virus.

The best way to avoid EEE is to prevent mosquito bites. 

Mosquito bite prevention tips:

  • bug sprayUse insect repellent to prevent mosquito bites. To find a repellent right for you, use the Environmental Protection Agency’s insect repellent search tool:
  • Wear long sleeves, pants, shoes, and socks when outdoors.
  • Repair screens on windows and doors to keep mosquitoes out of your home.
  • Reduce mosquito breeding conditions by eliminating standing water around your yard. Clean gutters and empty flower pots, tires, barrels, and other items that can hold water.

About Aerial Spraying

The product used by MDHHS for aerial treatment is called Merus 3.0. It will was sprayed by a low-flying aircraft at a very low volume of around one tablespoon per acre. Merus 3.0 is registered with the EPA. It is labeled for public health use over residential areas and is approved for use over organic crops.

No short-term or long-term risks to human health are expected during or after spraying. While it is not necessary to bring animals indoors during spraying, concerned pet owners can bring animals inside during spraying.

Application conducted at night minimizes risk to daytime foragers such as bees. The product dries quickly and should not pose long term risk. Beekeepers wanting to further minimize the risk that the product would be drawn into a colony can reduce entrances to their colonies to minimize air movement into the colony, or cover colonies during an application using a damp cloth -- burlap is often recommended.

Similar products are used and have been proved effective in other states, including Massachusetts. In Massachusetts, officials have been monitoring approximately 600 honeybee colonies and have not observed problems.

Large water bodies were avoided by MDHHS during spraying. The active ingredients in Merus 3.0 break down rapidly in surface water and are not expected to cause adverse effects.

More information

Washtenaw County Health Department
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