Eastern Equine Encephalitis (EEE)

When fall approaches, we often begin to see cases of Eastern Equine Encephalitis (EEE) in animals, such as horses, and in humans. In 2019, Michigan experienced its largest-ever outbreak of EEE, with 25% of the nation’s EEE cases diagnosed in the state. It is important to be informed and stay vigilant to protect yourself from mosquito-borne diseases. Below are some answers to frequently asked questions about EEE:


What is Eastern Equine Encephalitis (EEE)?
EEE is a rare, but serious zoonotic, viral disease that is spread by the bite of infected mosquitoes. The EEE virus can cause inflammation of the brain encephalitis. In the United States, approximately 5-10 EEE cases in humans are reported annually. It is one of the most dangerous mosquito-borne diseases in the United States. According to the Centers for Disease Control and Prevention (CDC), approximately one-third of the human cases of EEE are fatal.

Why are we seeing EEE cases in Michigan?
Michigan has had outbreaks of EEE about every decade since 1980 when the first human case was reported in the state. It is unknown exactly why some years are more severe than others, although weather, including temperature and rainfall, is thought to play a role.

How many total cases of EEE are there in Michigan this year?
As of September 22, 2020 there have been 33 confirmed cases of EEE across 13 counties- 30 cases in equine, two in deer and one in a human.

Are there efforts being taken at the community level to protect animals and people from EEE?
Many local communities monitor mosquito populations within their borders and deploy various mosquito control efforts when needed.
In District Health Department #10 jurisdiction, Mecosta, Newaygo, and Oceana counties have received aerial mosquito control treatment.

Why conduct aerial mosquito control treatment?

We are currently in a public health emergency and aerial applications provide the most effective option to suppress EEE outbreaks in high risk areas.  Aerial treatment can quickly reduce the number of mosquitoes in a large geographical area, therefore helping reduce the risk of transmission to humans and animals.

How does aerial mosquito control treatment work?

Licensed and certified mosquito control professionals apply EPA-registered insecticides as a ultra-low volume (ULV) spray from dusk until dawn in a specialized aircraft flying 300 feet in the air. The sprayer dispenses very fine aerosol droplets that drift in the air and kill adult mosquitoes on contact.

How do people get infected with EEE?
EEE is transmitted through the bite of an infected mosquito. You cannot get EEE directly from another person or from an animal.

How soon do people get sick after getting bitten by an infected mosquito?
It takes 4 to 10 days after the bite of an infected mosquito to develop symptoms of EEE.

Who is at risk for infection with EEE?
Anyone in an area where the virus is circulating in mosquitoes can get infected with EEE. The risk is highest for people who live in or visit woodland habitats, and people who work outside or participate in outdoor recreational activities, because of greater exposure to potentially infected mosquitoes. Those who are over 50 years old and under 15 years old are at increased risk of infection.

What are the symptoms of EEE disease?
Signs of EEE infection include the sudden onset of fever, chills, and body and joint aches. EEE infection can develop into severe encephalitis, resulting in headache, disorientation, tremors, seizures and paralysis. Permanent brain damage, coma and death may also occur in some cases. Approximately a third of patients who develop EEE die, and many of those who survive have mild to severe brain damage.

How do I get tested for EEE?
People who have been bitten by mosquitoes can monitor their health and talk with their healthcare provider if they develop symptoms such as fever, malaise, headache and confusion. Testing for EEE is not indicated in a person who is not showing signs suggestive of EEE illness.

How is EEE diagnosed?
Diagnosis is based on tests of blood or spinal fluid. These tests typically look for antibodies that the body makes against the viral infection.

What is the treatment for EEE?
There is no specific treatment for EEE. Antibiotics are not effective against viruses, and no effective anti-viral drugs have been discovered. Severe illnesses are treated by supportive therapy which may include hospitalization, respiratory support, IV fluids and prevention of other infections.

How can people reduce the chance of getting infected with EEE?

  • Avoid being outdoors between dusk and dawn when mosquitoes that carry EEE virus are most active.
  • Apply insect repellents that contain the active ingredient DEET, or other U.S. Environmental Protection Agency-registered product to exposed skin or clothing, and always follow the manufacturer’s directions for use.
  • Wear long-sleeved shirts and long pants when outdoors. Apply insect repellent to clothing to help prevent bites.
  • Maintain window and door screening to help keep mosquitoes outside.
  • Empty water from mosquito breeding sites around the home, such as buckets, unused kiddie pools, old tires or similar sites where mosquitoes may lay eggs.
  • Use nets and/or fans over outdoor eating areas.

Can my animal get EEE?
EEE is rare in dogs and cats, however, when cases have been identified in dogs, they’re typically less than six months old. Horses and birds are very susceptible to EEE and approximately 90 percent of horses that show signs of EEE die from the disease. A vaccine is also available and highly encouraged for horses.

How do I protect my pets from EEE?
Keep pets indoors as much as possible between dusk and dawn, when mosquitoes are most active. Mosquito repellents labeled for use on people should not be used on pets. There are some topical products that can be applied to dogs to protect them from mosquitoes; concerned pet owners should work with their veterinarian.

How do I protect my livestock from EEE?

Keep animals in a barn under fans during peak mosquito activity time, between dawn and dusk. Use an insect repellant on the animals that is approved for the species and eliminate standing water on the property.


  • For the updated information on EEE in Michigan, including case count, visit www.Michigan.gov/EEE
  • For general health information related to EEE, visit: www.cdc.gov/EEE
  • For general EEE questions, contact MDHHS at: (888) 535-6136. You can also email MDHHS at eee@michigan.gov.