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What is eastern equine encephalitis (EEE)?

Eastern equine encephalitis (EEE) belongs to a category of viruses known as arboviruses, or arthropod-borne viruses. Arboviruses are spread by the bites of blood-sucking insects, such as mosquitos and ticks. EEE is spread by the bite of certain kinds of mosquitoes.

What are the risk factors of EEE?

The overall risk of becoming infected with EEE depends on:

  • Exposure to mosquitoes: People who spend a lot of time outdoors or live in wooded areas have a greater chance of being bitten by mosquito.
  • Time of year and day: In the United States, cases of EEE tend to occur from late spring to early fall. Many kinds of mosquitoes are most active during dusk and dawn and during the early evening hours.
  • Geographic region: Most cases of EEE have been reported in Atlantic and Gulf coast states. Southeastern Massachusetts, particularly Plymouth and Bristol counties, have historically been "hot spots" for EEE. The Massachusetts Department of Public Health monitors mosquito populations, tests mosquitoes for virus, and calculates risks for each town.

Some people with EEE may develop a severe infection that causes brain tissue to become inflamed (encephalitis).The factors that increase one’s risk of getting a severe EEE infection include:

  • Age: Although people of any age can develop a serious infection, the risk is higher for adults older than 50 and children younger than 15.
  • Immune system: People who have a weakened immune system due to cancer treatments or organ transplantation are more at risk of developing a severe infection.

Eastern Equine Encephalitis (EEE) | Diagnosis & Treatments

How is EEE diagnosed?

  • Blood tests. Someone who is infected with EEE will have an increased level of antibodies in their blood. Antibodies are proteins produced by the immune system that attack foreign substances such as viruses and bacteria. Increased levels of antibodies are a sign that your immune system is fighting the virus.
  • A CT scan produces detailed, cross-sectional images of the brain. The results from a CT scan can rule out other possible diseases that may be causing inflammation.
  • Magnetic resonance imaging (MRI) is another procedure that takes detailed x-ray images of the brain to help detect brain inflammation.
  • A lumbar puncture (spinal tap) may be used to take a small sample of cerebral spinal fluid to determine if a child has EEE or other problems.
  • An electroencephalogram (EEG) can be used to detect small seizures in the brain that may not be obvious from watching the person. An EEG works by recording the brain's continuous electrical activity using stickers attached to the scalp that measure electrical activity.
  • A needle biopsy may be used to take a sample of brain tissue to determine the underlying cause of the inflammation.

How is EEE treated?

Although there is no specific treatment for EEE, there are several ways to help manage the symptoms of the disease:

  • Anticonvulsants for seizures
  • Eespirator for breathing problems
  • Pain relievers for headache, fever, or body ache
  • Sedatives for irritability or restlessness
  • Corticosteroids for brain swelling

How can I prevent EEE?

Avoiding mosquito bites is the easiest and most effective way to prevent EEE. Listed below are some ways you can protect your children:

  • Dress them in socks, pants, and long-sleeved shirts that cover their skin.
  • Avoid areas where mosquitoes are abundant, especially at times when mosquitoes are active.
  • Install and fix window screens to prevent mosquitoes from entering your home.
  • Empty buckets, toys, and other items that hold water in which mosquitoes develop.
  • Make sure your roof gutters are clean of leaves and drain well.
  • Contact your local mosquito control district to learn of other options to reduce mosquito problems.
  • Use insect repellents carefully and wisely.

The easiest and most effective way to avoid mosquito bites is by using insect repellant. There are many products that are made to prevent mosquito bites. Experts from the American Academy of Pediatrics (AAP) recommend one that can be applied directly to the skin that is particularly effective: DEET (usually listed on labels as N,N-diethyl-m-toluamide).

The amount of DEET in insect repellents varies and may range from less than 10 percent to more than 30 percent. Products with higher concentrations of DEET tend to provide longer protection and need to be applied less frequently. According to the AAP, products that have around 10 percent DEET may keep away insects for nearly two hours, while products with about 24 percent DEET last an average of five hours.

Other repellents contain yet other active ingredients (other than DEET). Select a repellent that is registered with the federal Environmental Protection Agency. Read and follow directions to use them properly. The AAP does not recommend insect repellants for children younger than 2 months.

Here are additional dos and don'ts on how to use insect repellent

  • DO apply repellent to all exposed skin areas and to clothing.
  • DO spray repellent in your hands first and then gently rub it on a child's face, avoiding the eyes and mouth.
  • DO use aerosols and pump sprays to ensure that the repellant is applied evenly.
  • DO use repellants with higher concentrations if there will be a long time between applications or if you will be in environments where mosquito populations are high.
  • DO wash repellent off once you get back indoors.
  • DON'T use insect repellent on skin that is already covered by clothing.
  • DON'T apply repellant directly onto a child's face.
  • DON'T keep using a repellent if it gives you a rash or other skin reaction.

Eastern Equine Encephalitis (EEE) | Programs & Services