Eastern Equine Encephalitis

EEE virus is a rare cause of brain infections (encephalitis). Only a few cases are reported in the United States each year. Most occur in eastern or Gulf Coast states. Approximately 30% of people with EEE die and many survivors have ongoing neurologic problems.

Alphavirus

Symptoms & Treatment

• Symptoms
• Treatment

Symptoms

The incubation period for Eastern equine encephalitis virus (EEEV) disease (the time from infected mosquito bite to onset of illness) ranges from 4 to 10 days. EEEV infection can result in one of two types of illness, systemic or encephalitic (involving swelling of the brain, referred to below as EEE). The type of illness will depend on the age of the person and other host factors. It is possible that some people who become infected with EEEV may be asymptomatic (will not develop any symptoms).

Systemic infection has an abrupt onset and is characterized by chills, fever, malaise, arthralgia, and myalgia. The illness lasts 1 to 2 weeks, and recovery is complete when there is no central nervous system involvement. In infants, the encephalitic form is characterized by abrupt onset; in older children and adults, encephalitis is manifested after a few days of systemic illness. Signs and symptoms in encephalitic patients are fever, headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, cyanosis, convulsions, and coma.

Approximately a third of all people with EEE die from the disease. Death usually occurs 2 to 10 days after onset of symptoms but can occur much later. Of those who recover, many are left with disabling and progressive mental and physical sequelae, which can range from minimal brain dysfunction to severe intellectual impairment, personality disorders, seizures, paralysis, and cranial nerve dysfunction. Many patients with severe sequelae die within a few years.

Eastern equine encephalitis

Treatment

No human vaccine against EEEV infection or specific antiviral treatment for clinical EEEV infections is available. Patients with suspected EEE should be evaluated by a healthcare provider, appropriate serologic and other diagnostic tests ordered, and supportive treatment provided.

Clinical Evaluation (for Health Care Providers)

Cerebrospinal fluid (CSF) findings include neutrophil-predominant pleocytosis and elevated protein levels; glucose levels are normal. Brain lesions are typical of encephalomyelitis and include neuronal destruction and vasculitis, which is perivascular and parenchymous at the cortex, midbrain, and brain stem. There is minimal involvement of the spinal cord.

EEEV is difficult to isolate from clinical samples; almost all isolates (and positive PCR results) have come from brain tissue or CSF. Serologic testing remains the primary method for diagnosing EEEV infection. Combined with a consistent clinical presentation in an endemic area, a rapid and accurate diagnosis of acute neuroinvasive EEEV disease can be made by the detection of EEEV-specific IgM antibody in serum or CSF. EEEV IgM tests are available commercially, in some state health department laboratories, and at CDC. A positive EEEV IgM test result should be confirmed by neutralizing antibody testing of acute- and convalescent-phase serum specimens at a state public health laboratory or CDC. To submit specimens for testing at CDC, please contact your state health department.

All EEEV disease cases should be reported to local public health authorities. Reporting can assist local, state and national authorities to recognize outbreaks of this rare disease and to institute control measures to limit future infections.

Eastern equine encephalitis incidence map

Transmission

Eastern equine encephalitis virus (EEEV) is maintained in a cycle between Culiseta melanura mosquitoes and avian hosts in freshwater hardwood swamps. Cs. melanura is not considered to be an important vector of EEEV to humans because it feeds almost exclusively on birds. Transmission to humans requires mosquito species capable of creating a “bridge” between infected birds and uninfected mammals such as some Aedes, Coquillettidia, and Culex species.

Horses are susceptible to EEEV infection and some cases are fatal. EEEV infections in horses, however, are not a significant risk factor for human infection 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).

Eastern Equine Encephalitis Virus

Arboviral Diagnostic Testing

Preliminary diagnosis is often based on the patient’s clinical features, places and dates of travel (if patient is from a non-endemic country or area), activities, and epidemiologic history of the location where infection occurred.

Laboratory diagnosis of arboviral infections is generally accomplished by testing of serum or cerebrospinal fluid (CSF) to detect virus-specific IgM and neutralizing antibodies.

In fatal cases, nucleic acid amplification, histopathology with immunohistochemistry and virus culture of autopsy tissues can also be useful. Only a few state laboratories or other specialized laboratories, including those at CDC, are capable of doing this specialized testing.

Instructions for sending diagnostic specimens to the DVBID Arbovirus Diagnostic Laboratory.

Test results are normally available 4 to 14 days after specimen receipt. Reporting times for test results may be longer during summer months when arbovirus activity increases. Receipt of a hard copy of the results will take at least 2 weeks after testing is completed. Initial serological testing will be performed using IgM capture ELISA, MIA (Microsphere-Based Immunoassay) and IgG ELISA. If the initial results are positive, further confirmatory testing may delay the reporting of final results. ALL RESULTS WILL BE SENT TO THE APPROPRIATE STATE HEALTH DEPARTMENT. Notify your state health department of any submissions to CDC.

Prevention

The most effective way to prevent infection from ­­­Eastern Equine Encephalitis virus is to prevent mosquito bites. Mosquitoes bite during the day and night. 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 repellentsExternal 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

Find the right insect repellent for you by using EPA’s search toolExternal.

Tips for babies and children

• Always follow instructions when applying insect repellent to children.
• Do not use insect repellent on babies younger than 2 months old.
  • Instead, dress your child in clothing that covers arms and legs.
  • Cover strollers and baby carriers with mosquito netting.
• 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.
• Visit the EPA website to learn more.External

Wear long-sleeved shirts and long pants

Treat clothing and gear

• Use 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 indoors and outdoors.

Prevent mosquito bites when traveling overseas

• Choose a hotel or lodging with air conditioning or screens on windows and doors.
• Sleep under a mosquito bed net if you are outside or in a room that does not have screens.
  • Buy a bed net at your local outdoor store or online before traveling overseas.
  • Choose a WHOPES-approved bed net: compact, white, rectangular, with 156 holes per square inch, and long enough to tuck under the mattress.
  • Permethrin-treated bed nets provide more protection than untreated nets.
    • Do not wash bed nets or expose them to sunlight. This will break down the insecticide more quickly.
  • For more information on bed nets, visit CDC’s page on insecticide-treated bed nets.
  • For more information on traveling overseas, visit Travelers’ Health.

Eastern Equine Encephalitis Resources
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