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.

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Alphavirus

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 a systemic febrile illness 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 host factors. Some people who become infected with EEEV may be asymptomatic (will not develop any symptoms).

Eastern equine encephalitis incidence map

• Systemic infection is characterized by fever, chills, malaise, arthralgia, and myalgia. 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 EEEV infection die. Death usually occurs 2 to 10 days after onset of symptoms but can occur much later. Of those who recover, many are left with physical or mental sequelae, which can range from mild brain dysfunction to severe intellectual impairment, personality disorders, seizures, paralysis, and cranial nerve dysfunction. Many patients with severe sequelae require long-term care and die within a few years.

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Eastern equine encephalitis

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 certain cases, molecular testing can also be used.
• For some cases (particularly 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.

Tests

• 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/or IgG ELISA. If the initial results are positive, further confirmatory testing may delay the reporting of final results.

Treatment

• There is no approved human vaccine or specific antiviral treatment for EEEV infections. Patients with suspected EEEV disease should be evaluated by a healthcare provider, appropriate serologic and other diagnostic tests ordered, and supportive treatment provided.

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Eastern Equine Encephalitis Virus

Transmission

• Image of Eastern equine encephalitis transmission cycle.
• Another arrow points from the birds to another mosquito and then to the figures of a horse and person.
• People and horses can become infected when a bridge vector, a mosquito species that feeds on many kinds of animals, feeds on an infected bird and then bites people or horses.
• People and horses are considered dead-end hosts because, unlike birds, they can’t pass the virus on to other biting mosquitoes.
• 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.

Mosquito bridge

• 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 many 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).

Vaccine for horses

• There is a vaccine to prevent EEEV infection in horses.

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Eastern equine encephalitis head scans

Clinical Evaluation

• Cerebrospinal fluid (CSF) findings include neutrophil-predominant pleocytosis and elevated protein levels; glucose levels are normal. Neuroimaging shows brain lesions consistent with encephalitis, including neuronal destruction and vasculitis in 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 PCR positive samples) 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 EEEV disease can be made by the detection of EEEV-specific IgM antibody in serum or CSF.
• EEEV IgM testing is available at CDC and some state health departments.
• A positive EEEV IgM test result should be confirmed by neutralizing antibody testing 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.

Prevention

• Mosquito control is something anyone can do, ranging from individual home owners to professionals.
• You can control mosquitoes in your home.
• You, your neighbors, and the community can also take steps to reduce mosquitoes in and around your home and in your neighborhood.
• Professionals from local government departments or mosquito control districts develop mosquito control plans, perform tasks to control larvae and adult mosquitoes, and evaluate the effectiveness of actions taken.

Tips for babies and children

• Adult applying insect repellent to a child’s face.
• 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.

Insect 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
• Treat clothing and gear with permethrin
• 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.

Mosquito control measures

• Use screens on windows and doors
• 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.

Eastern equine encephalitis Resources
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