Eastern Equine Encephalitis (EEE)

Overview

What is eastern equine encephalitis?

Eastern equine encephalitis (EEE), is a rare disease that causes inflammation of the brain (encephalitis). It is caused by an arbovirus, which means it is spread through the bite of infected mosquitoes. It was first seen in horses (equine) in the 1830s and first diagnosed in a human along the east coast in the 1930s. The virus can only be spread to humans through a mosquito bite. It cannot be spread from human to human or from horse or other animal to a human.

How do the mosquitoes become infected with eastern equine encephalitis (EEE) virus?

Certain types of mosquitoes become infected by feeding on birds infected with eastern equine encephalitis (EEE) virus. These mosquitoes then bite humans and animals. The birds themselves originally became infected by being bit by yet a different species of mosquito.

How many people get infected with eastern equine encephalitis (EEE)?

According to the Centers for Disease Control, between three and 15 cases of eastern equine encephalitis are typically reported in the United States each year. However, in a recent year, health officials report a doubling of the number people who have contracted the virus.

Where are the mosquitos that carry eastern equine encephalitis (EEE) virus found?

Today, eastern equine encephalitis (EEE) is found in North, South and Central America and in the Caribbean islands. More specifically, in the United States, most eastern equine encephalitis cases have been reported from the Gulf Coast and Atlantic Coastline states and states bordering the Great Lakes. Florida, Massachusetts, New York, North Carolina, Michigan and Georgia have been the states with the largest number of reported cases of EEE.

What time of year are people most likely to get eastern equine encephalitis (EEE)?

Eastern equine encephalitis (EEE) cases are reported mostly from late spring through early fall, with the peak occurring during the summer months.

Can I die from being bite by a mosquito infected with eastern equine encephalitis (EEE) virus?

Fortunately, only about 5% of people who are bit by a mosquito infected with eastern equine encephalitis (EEE) develop eastern equine encephalitis. However, about one in three people who do develop EEE die from it. Many survivors have mild to severe brain damage.

Symptoms and Causes

What are the symptoms of eastern equine encephalitis (EEE)?

Some people bitten by a mosquito infected with eastern equine encephalitis (EEE) virus may not develop any symptoms at all. For those who do develop symptoms, symptoms usually appear four to 10 days after being bitten.

Symptoms of mild, general EEE infection include:

  • Muscle aches.
  • Fever.
  • General feeling of discomfort.
  • Weakness
  • Joint pain.
  • Neck stiffness.
  • Chills.

Symptoms can last one to two weeks. However, tiredness and weakness may last for weeks to months.

Symptoms of severe infection – encephalitis (inflammation of the brain) – include:

  • High fever.
  • Headache.
  • Drowsiness.
  • Vomiting.
  • Diarrhea.
  • Loss of appetite.
  • Irritability/restlessness.
  • Confusion.
  • Seizures.
  • Coma.

Recovery from severe infection may take several weeks or months.

Diagnosis and Tests

How is eastern equine encephalitis (EEE) virus diagnosed?

Eastern equine encephalitis (EEE) virus is diagnosed based on the results of blood or spinal fluid tests. These tests look for antibodies your body makes in a defense response to being attacked by the virus.

Management and Treatment

What is the treatment for eastern equine encephalitis?

There are no vaccines or anti-viral medications to treat eastern equine encephalitis (EEE). Antibiotics are not used to treat viruses. Serious cases of EEE are treated in the hospital. Patients receive “supportive care,” which consists of IV fluids, breathing assistance, and prevention of other infections.

Who is most at risk for infection with eastern equine encephalitis (EEE) virus?

People most at risk include:

  • People who live in the areas of the country where virus-infected mosquitos are found, which are mostly wetland/swamp or woodland areas.
  • People who work or spend a lot of time outside and especially during dawn and dusk – times when mosquitoes are most active.
  • Adolescents (age 15 and under) and adults over the age of 50.
  • People with weakened immune systems due to cancer treatment, organ transplantation or presence of other diseases (including diabetes, high blood pressure, kidney disease) or infections.

Prevention

How can I protect myself and my family from possible infection with the eastern equine encephalitis (EEE) virus?

  • Cover all exposed skin and/or clothing with an insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus. Carefully read instructions for use of these products in children under age 3.
  • Wear long sleeves, pants and hat when outside and especially when hiking in wooded areas or enjoying time near water.
  • Empty all standing water that collects outside your home – from birdbaths, buckets/pots, sprinkling cans, trash containers, flower pots, toys and kiddie pools. Standing water is a breeding ground for mosquitos.
  • Use screens on doors and windows. Make sure screens are intact; repair any holes.
  • Avoid outside time at dawn and dusk if possible (or follow tips above). These are the times when mosquitos are most active.

Outlook / Prognosis

What should I do if I’m worried I may have been bitten by a mosquito carrying the eastern equine encephalitis (EEE) virus?

First, keep in mind that only a small percentage of people – about 5% of those bitten by a EEE-infected mosquito – go on to develop encephalitis. Most people who are bitten by an EEE-infected mosquito have no symptoms or only have mild, flu-like symptoms. However, if you or your loved one suddenly develop symptoms of EEE, call your doctor right away. Your doctor will further evaluate your symptoms, order blood or spinal fluid testing (if necessary) and decide on the need for additional medical care.

Last reviewed by a Cleveland Clinic medical professional on 10/22/2019.

References

  • Vector Disease Control International. Eastern Equine Encephalitis Virus. (http://www.vdci.net/vector-borne-diseases/eastern-equine-encephalitis-virus-education-and-integrated-mosquito-management-to-protect-public-health) Accessed 10/10/2019.
  • Centers for Disease Control and Prevention. Eastern Equine Encephalitis. (https://www.cdc.gov/easternequineencephalitis/index.html) Accessed 10/10/2019.

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