Eastern equine encephalitis (Triple E) is an illness caused by a virus that comes from an infected mosquito bite. Most people who are infected have no symptoms, but some may develop fever, headaches, and vomiting. Symptoms occur within 4-10 days of being infected and most recover in 1-2 weeks. A small number will develop swelling of the brain and severe neurological symptoms that can be permanent. Triple E can also lead to coma and death.

This condition is caused by a type of arbovirus and is transmitted by a mosquito which has bitten an infected bird or reptile. Diagnosis is based on the symptoms, specific findings in the blood, and occasionally by an MRI of the brain.

There is no specific treatment for Triple E. It is managed by taking care of the symptoms. Prevention includes avoiding mosquito bites and controlling mosquito populations.

What is eastern equine encephalitis (EEE)?

EEE is a rare disease caused by a virus spread by infected mosquitoes. EEE virus is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain (encephalitis). In the United States, an average of 11 human cases of EEE are reported annually.

How do people get infected with EEE virus?

EEE virus is transmitted through the bite of an infected mosquito. It does not spread through coughing, sneezing, or touching. In a very small number of cases, EEE virus has been spread through organ donation from an infected donor.

Where and when have most cases of EEE occurred?

Most cases of EEE have been reported from Atlantic and Gulf Coast states. Cases have also been reported from the Great Lakes region. EEE disease cases occur primarily from late spring through early fall, but in subtropical endemic areas (e.g., the Gulf States), rare cases can occur in winter.

Who is at risk for infection with EEEV?

Anyone in an area where the virus is circulating can get infected with EEE virus. The risk is highest for people who live, work, or participate in outdoor activities in or around wooded swampy areas in the eastern United States.

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.

What are the symptoms of EEE?

Most people who become infected with EEE virus show either no or mild symptoms such as fever. Severe cases of EEE include encephalitis (swelling of the brain) or meningitis (swelling of the membranes that surround the brain and spinal cord) and begin with the sudden onset of fever, chills, headache, and vomiting. The illness may then progress into disorientation, seizures, and coma. Approximately a third of patients who develop encephalitis due to EEE virus die, and many of those who survive have mild to severe brain damage.

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 virus?

There is no approved vaccine for people or preventive medicine. The best way to prevent EEE is to prevent mosquito bites.

• Use insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus.
• The repellent/insecticide permethrin can be used on clothing to protect through several washes. Always follow the directions on the package.
• Wear long sleeves and pants when weather permits.
• Have secure, intact screens on windows and doors to keep mosquitoes out.
• Eliminate mosquito breeding sites by emptying standing water from flowerpots, buckets, barrels, and other containers. Drill holes in tire swings so water drains out. Keep children’s wading pools empty and on their sides when they aren’t being used.

What should I do if I think a family member might have EEE?

Consult your healthcare provider for proper diagnosis.

Eastern equine encephalitis virus (EEEV) is a member of the genus Alphavirus, family Togaviridae. Other medically important alphaviruses found in the Americas include Western equine encephalitis virus (WEEV) and Venezuelan equine encephalitis virus (VEEV). EEEV has a single-stranded, positive-sense RNA genome. The virus particles are spherical and have a diameter of 60-65 nm. Of the four lineages of EEEV, Group I is endemic in North America and the Caribbean and causes most human disease cases; the other three groups (IIA, IIB, and III) cause primarily equine illness in Central and South America.

Eastern equine encephalitis (EEE) virus is maintained in a cycle between Culiseta melanura mosquitoes and avian hosts in freshwater hardwood swamps. Culiseta melanura is not considered to be an important vector of EEE virus to people because it feeds almost exclusively on birds. Transmission to people requires another mosquito species to create a “bridge” between infected birds and uninfected mammals, such as people or horses. Most of the bridge species are within the Aedes, Coquillettidia, and Culex genera. EEE virus has been documented to be transmitted through organ transplantation with one organ donor transmitting the infection to three organ transplant recipients.

Horses are susceptible to EEE virus infection and many cases are fatal. EEE virus infections in horses, however, do not increase risk for human infections because horses (like humans) are considered to be “dead-end” hosts for the virus (i.e., the concentration of virus in their bloodstreams is usually insufficient to infect mosquitoes). There is a vaccine to prevent EEE virus infection in horses.

Most people infected with eastern equine encephalitis (EEE) virus do not develop symptoms. For those who develop symptoms, the time from infected mosquito bite to onset of illness (incubation period) ranges from 4 to 10 days.

EEE can result in febrile illness (fever) or neurologic disease, including meningitis (infection of the membranes that surround the brain and spinal cord) or encephalitis (infection of the brain). The type of illness will depend on the age of the person and other factors.

Febrile illness is characterized by fever, chills, body aches, and joint pain. The illness lasts 1 to 2 weeks, and most people recover completely when there is no central nervous system involvement.

Signs and symptoms of neurologic disease include fever, headache, vomiting, diarrhea, seizures, behavioral changes, drowsiness, and coma. In infants, neurologic disease often occurs soon after onset; in older children and adults, encephalitis may occur after several days of systemic illness.

• Approximately a third of all people with encephalitis due to EEE die. Death usually occurs 2 to 10 days after onset of symptoms but can occur much later.
• Many people who recover are left with long-term physical or mental impairments, which can range from mild brain dysfunction to severe intellectual impairment, personality disorders, seizures, paralysis, and cranial nerve dysfunction.
• People with severe impairments often require long-term care and die within a few years.

If you think you or a family member might have EEE, talk with your health care provider.

• Healthcare providers diagnose EEE virus infection based on:
  • Signs and symptoms
  • History of living in or traveling to an area where EEE virus is known to circulate
  • History of possible exposure to the mosquitoes that can carry EEE virus
  • Laboratory testing of blood or spinal fluid
• Your healthcare provider can order tests to look for EEE virus infection or other infections that can cause similar symptoms.

There are no medications to prevent or treat EEE virus infections. Antibiotics are not effective against viruses, such as EEE virus.

Rest, fluids, and over-the-counter pain medications may relieve some symptoms.

For severe disease, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

Eastern equine encephalitis (EEE) is spread to people through the bite of an infected mosquito. Mosquitoes bite during the day and night. There is no vaccine to prevent EEE virus infection. The best way to prevent EEE is to protect yourself from mosquito bites. Use insect repellent, wear long-sleeved shirts and pants, treat clothing and gear, and take steps to control mosquitoes indoors and outdoors.

Protect Yourself and Your Family from Mosquito Bites

Use insect repellent

Use Environmental Protection Agency (EPA)-registered insect repellents with one of the active ingredients below. When used as directed, EPA-registered insect repellents are proven safe and effective, even for pregnant and breastfeeding women.

• DEET
• Picaridin (known as KBR 3023 and icaridin outside the US)
• IR3535
• Oil of lemon eucalyptus (OLE)
• Para-menthane-diol (PMD)
• 2-undecanone

Tips for babies and children

• Dress your child in clothing that covers arms and legs.
• Cover strollers and baby carriers with mosquito netting.
• When using insect repellent on your child:
  • Always follow label instructions.
  • Do not use products containing oil of lemon eucalyptus (OLE) or para-menthane-diol (PMD) on children under 3 years old.
  • Do not apply insect repellent to a child’s hands, eyes, mouth, cuts, or irritated skin.
    • Adults: Spray insect repellent onto your hands and then apply to a child’s face.

Tips for everyone

• Always follow the product label instructions.
• Reapply insect repellent as directed.
  • Do not spray repellent on the skin under clothing.
  • If you are also using sunscreen, apply sunscreen first and insect repellent second.

Natural insect repellents (repellents not registered with EPA)

• We do not know the effectiveness of non-EPA registered insect repellents, including some natural repellents.
• To protect yourself against diseases spread by mosquitoes, CDC and EPA recommend using an EPA-registered insect repellent.
• Choosing an EPA-registered repellent ensures the EPA has evaluated the product for effectiveness.

Wear long-sleeved shirts and long pants

Treat clothing and gear

• Use 0.5% permethrin to treat clothing and gear (such as boots, pants, socks, and tents) or buy permethrin-treated clothing and gear.
  • Permethrin is an insecticide that kills or repels mosquitoes.
  • Permethrin-treated clothing provides protection after multiple washings.
  • Read product information to find out how long the protection will last.
• If treating items yourself, follow the product instructions.
• Do not use permethrin products directly on skin.

Take steps to control mosquitoes indoors and outdoors

• Use screens on windows and doors. Repair holes in screens to keep mosquitoes outdoors.
• Use air conditioning, if available.
• Stop mosquitoes from laying eggs in or near water.
  • Once a week, empty and scrub, turn over, cover, or throw out items that hold water, such as tires, buckets, planters, toys, pools, birdbaths, flowerpots, or trash containers.
  • Check for water-holding containers both indoors and outdoors.

Prevent Mosquito Bites When Traveling Overseas

Remember to pack the following items

• EPA-registered insect repellents
• Long-sleeved shirts and long pants. Mosquitoes may bite through thin clothing.
• Clothing and gear (such as boots, pants, socks, tents) treated with 0.5% permethrin. You can treat your own items or purchase permethrin-treated clothing and gear.
• Mosquito net if you will be sleeping outside or when screened rooms are not available.

Keep mosquitoes out of your hotel room or lodging

• Choose a hotel or lodging with air conditioning or window and door screens.
• Use a mosquito net if you are unable to stay in a place with air conditioning or window and door screens or if you are sleeping outside.

Sleep under a mosquito net

Sleep under a mosquito net if you are outside or when screened rooms are not available. Mosquitoes can live indoors and bite during the day and night.

• Buy a mosquito net at your local outdoor store or online before traveling overseas.
• Choose a mosquito net that is compact, white, rectangular, with 156 holes per square inch, and long enough to tuck under the mattress.
• Permethrin-treated mosquito nets provide more protection than untreated nets.
  • Permethrin is an insecticide that kills mosquitoes and other insects.
  • To determine if you can wash a treated mosquito net, follow the label instructions.

Use mosquito nets correctly

Mosquito nets can be hung above a bed or crib to protect against mosquito bites. Adults and children should sleep under a mosquito net if air conditioned and screened rooms are not available.

When using a mosquito net:

• Tuck the net under the mattress to keep the mosquitoes out.
• Tuck netting under the crib mattress or select a mosquito net long enough to touch the floor.
• Pull the net tightly to avoid choking hazards for young children. Check label instructions for additional information.
• Hook or tie the sides of the net to other objects if they are sagging in towards the sleeping area.
• Check for holes or tears in the net where mosquitoes can enter.
• DO NOT hang the net near any candles, cigarettes, or open fires, as it can catch on fire.
• DO NOT sleep directly against the net, as mosquitoes can still bite through holes in the net.