DETROIT – Aerial pesticides will be sprayed in Michigan starting Sunday to kill mosquitoes as health officials work to combat the worst outbreak of mosquito-borne Eastern equine encephalitis in the state’s history.

Michigan now has nine confirmed human cases of EEE this year, with three fatalities. Those affected have ranged in age from 14 to 78.

In addition, there have been 27 confirmed animal cases – 14 horses, 11 whitetail deer and two Mexican gray wolf pups at a Battle Creek zoo, according to Mary Grace Stobierski, state public health veterinarian and manager in the zoonotic and infectious diseases division at Michigan Department of Health.

There is no treatment or cure for EEE, a rare virus spread by mosquitoes that kills 33% of people who are sickened by it. Those who survive severe EEE illness are often left with long-term neurological problems.

The state last sprayed mosquitoes in 1980, though communities have sprayed locally to fight outbreaks of the West Nile virus and to control mosquitoes as a nuisance, Stobierski said.

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The aerial spraying program will cover 1,125 square miles over 14 counties at high risk for EEE, mostly in southwestern and mid-Michigan. It is expected to cost between $1.5 million-$1.8 million.

Weather-permitting, spraying will begin at 8 p.m. Sunday in portions of Allegan, Barry, Berrien, Branch, Calhoun, Cass, Jackson, Kalamazoo, Kent, Lapeer, Montcalm, Newaygo, St. Joseph and Van Buren counties.

Because of continuing warm weather and the rise in the number of EEE cases and growing number of high-risk areas in Michigan, pesticide spraying was chosen as a tactic to try to slow the rate of infections.

“We are taking this step to help protect the health and safety of Michiganders in areas of the state that are being affected by this dangerous mosquito-borne disease,” said Dr. Joneigh Khaldun, the state’s chief medical executive, in a news release. “The continuing number of cases in both people and animals indicate an ongoing risk for EEE exposure. We continue to urge residents to protect themselves against mosquito bites until a hard frost.”

The spraying program will be conducted by low-flying twin-engine aircraft beginning about 8 p.m. Sunday and continuing until 4:30 a.m. the next morning in areas of concern, although the timing could change depending on weather.

Mosquito-control professionals will apply an organic pesticide called Merus 3.0, which contains 5% pyrethrin. Pyrethrins are chemicals found naturally in some chrysanthemum flowers. They are a mixture of six chemicals that are toxic to insects.

Two other states with EEE outbreaks – Massachusetts and Rhode Island – also have used aerial spraying to combat EEE, health officials said.

"With the continuing warm weather we do not see any reduction in mosquito populations in the immediate future," said Dr. Sarah Lyon-Callo, state epidemiologist.

"We are applying about one tablespoon of insecticide per acre, which is about football-field size.”

The efficacy rate is expected to be as high as 85% at killing mosquitoes, said Laura McGowan, a representative from Clarke, the contractor that will conduct the aerial spraying.

Aerial spraying is not expected to have any impact on surface water or drinking water.

The pesticides being used, McGowan said, "are toxic to things like bees and other beneficial insects. However, the way we impact that is to ensure that when we do our applications, nontarget insects are not in the exposure area. Obviously, that's why we do our applications between the hours of dusk and dawn, for example, when bees are in the hive and monarchs are protected. So there should be no anticipated nontarget impacts for other beneficial insects."

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In general, health risks for people also are not expected during or after spraying, said Dr. Joost Vant Erve, a toxicologist specialist in the state division of environmental health.

However, he said, "if you are concerned about exposure to insecticides, or have known sensitivities such as if you've had a previous allergic reaction to pyrethrin or have asthma, out of an abundance of caution, some of the ways that you can reduce your exposure are to:

Remain inside during the hours that spraying will occur.

Close windows and doors and turn off any air conditioners and window vents that bring outside air inside

Bring outdoor items such as laundry, other furniture and children's toys inside or cover them.

Keep pets indoors

Cover swimming pools."

Contributing: The Associated Press. Follow Kristen Jordan Shamus on Twitter @kristenshamus.