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Public Health Response to Eastern Equine Encephalitis (EEE)

Friday September 27, 2019

The Michigan Department of Health & Human Services and 12 local health departments will be conducting aerial spraying in 14 counties to combat mosquito-borne disease.

This action is due to the large geographic distribution and number of Eastern Equine Encephalitis (EEE) cases in humans and/or animals, coupled with warm weather projections.

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Spraying is scheduled to take place starting Sunday, September 29th starting at 8 pm. However, the ability to spray is weather dependent and the schedule may change. Residents are encouraged to visit for up-to-date information.

Spraying will occur in St. Joseph and Branch counties, as well as 12 other counties outside of Branch-Hillsdale-St. Joseph Community Health Agency. Aerial spraying is conducted by low-flying aircraft, beginning in the early evening and continuing up until 4:30 am the next morning, in areas of concern. Mosquito control professionals will apply approved pesticides as an ultra-low volume (ULV) spray. ULV sprayers dispense very fine aerosol droplets that stay suspended in the air and kill adult mosquitoes on contact. This is a tactic other states, including Massachusetts and Rhode Island, have recently employed to combat EEE.

The pesticide being used is Merus 3.0 which is an organic pesticide containing 5 percent pyrethrin. Pyrethrins are chemicals found naturally in some chrysanthemum flowers. They are a mixture of six chemicals that are toxic to insects. Pyrethrins are commonly used to control mosquitoes, fleas, flies, moths, ants, and many other pests. Pyrethrins have been registered for use in pesticides since the 1950s.

In general, health risks are not expected during or after spraying. No special precautions are recommended; however, residents and individuals who have known sensitivities to pyrethrins can reduce potential for exposure by staying indoors during spraying. Aerial spraying is not expected to have any impacts on surface water or drinking water.

Aerial spraying will be conducted in the nighttime hours as this is when mosquitos are more active. It is also when fish are less likely to be at the surface feeding and honeybees are most likely to be in their hives. However, owners should cover small ornamental fishponds during the night of spraying. While it is not necessary to bring animals indoors during spraying, concerned pet owners can bring animals inside during spraying.

Additional information about aerial spraying and other health-related information is available in a Frequently Asked Questions document at
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As of September 27th, EEE has been confirmed in nine people, with three fatalities, in Barry, Berrien, Calhoun, Cass, Kalamazoo and Van Buren counties. In addition, cases have occurred in 27 animals from 13 counties: Barry, Berrien, Calhoun, Cass, Genesee, Jackson, Kalamazoo, Kent, Lapeer, Montcalm, Newaygo, St. Joseph and Van Buren. There is an EEE vaccine available for horses, but not for people. Additional animal cases are under investigation.

Although aerial spray is considered necessary to reduce human risk, it will not eliminate it. Rebecca Burns, Health Officer, reminds all residents of St. Joseph, Branch, and Hillsdale counties to, “be vigilant about protecting yourself and your family members from mosquito bites, especially those 15 years old and younger and those that are 50 years old and older who are more likely to develop a severe case of the EEE disease.”

Michigan residents can stay healthy by following these steps to avoid mosquito bites:

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