What is Eastern Equine Encephalitis?

Eastern equine encephalitis is a rare but serious disease caused by the Eastern equine encephalitis (EEE) virus, a member of the family Togaviridae, genus Alphavirus. Eastern equine encephalitis is found mainly along the eastern seaboard and Gulf coast of the United States. EEE is a mosquito borne infection of wild birds that can be transmitted to other birds, humans, horses and other animals by mosquitoes. In New Jersey, the principal bird vector for EEE is a freshwater swamp mosquito commonly found in the coastal plain of the southern half of the state. The salt marsh mosquito is the principal human vector of the virus in New Jersey, while more than one species of mosquito are known to transmit the virus to horses in the state.

Who gets Eastern Equine Encephalitis?

Anyone can get Eastern equine encephalitis, but the disease is more common in young children and in persons over the age of 55. In the last 30 years, New Jersey has averaged less than one confirmed human case of EEE every 5 years, and there have not been any confirmed cases in over 15 years. Most of the cases have been reported from coastal areas where the salt marsh mosquito is found. Outbreaks have occurred in 1959 (32 cases) and 1968 (12 cases). In addition to humans, other animals that can suffer severe disease include: equines (horses), certain birds such as pheasants, quail, ostriches and emus and, rarely, puppies.

How is Eastern Equine Encephalitis spread?

The Eastern equine encephalitis virus has a complex life cycle involving birds and a specific type of mosquito, Culiseta melanura, which lives in acid water swamps. These mosquitoes feed only on birds; they do not normally feed on humans or other mammals. Infected wild birds do not usually become ill with the disease. The natural cycle for EEE virus occurs nearly every year in some swamp habitats. In certain years the virus may become amplified in this bird-mosquito cycle, however, and other species of mosquitoes which feed on both birds and mammals act as “bridge vectors” and are capable of transmitting the virus to mammals, including horses and humans. The salt marsh mosquito, Ochlerotatus sollicitans, is the principal bridge vector that is capable of spreading the virus to humans in New Jersey. Both the salt marsh mosquito and a freshwater swamp mosquito, Coquillettidia perturbans, are important as bridge vectors of EEE to horses. The risk of becoming infected with EEE virus, while extremely low at all times, is highest from late July through early October. The mosquitoes that can transmit the virus are greatly reduced at about the time of the first frost in the in the fall. The overwintering cycle of the virus is not clearly understood.

What are the symptoms of Eastern Equine Encephalitis?

Infection with Eastern equine encephalitis virus can cause a range of illnesses. Most people infected with the virus have no symptoms; others get only a mild flu-like illness with fever, headache, and a sore throat. In rare cases, infection of the central nervous system occurs, causing sudden fever, muscle pains and a headache of increasing severity, often followed quickly by seizures and coma. In these rare instances, about one third of patients die from the disease. Of those who survive, many suffer permanent brain damage.

How soon do symptoms occur?

Symptoms usually occur 4 to 10 days after the bite of an infected mosquito.

How is Eastern Equine Encephalitis diagnosed?

Eastern equine encephalitis is diagnosed through tests of the blood or spinal fluid.

What is the treatment for Eastern Equine Encephalitis?

There is no specific treatment for Eastern equine encephalitis. Antibiotics are not effective against viruses, and anti-viral drugs have not been effective for treating EEE. Care of the patient centers on treatment of symptoms and complications.

Can you get EEE from horses or other people?

Only mosquitoes can transmit the EEE virus to humans. People and horses that are infected with the virus cannot spread the disease to others. In fact, even mosquitoes cannot be infected by feeding on humans or horses with the disease, since these are “dead end hosts” for the virus. Mosquitoes become infected with EEE after feeding on infected birds that serve as reservoir hosts for the virus.

How can Eastern Equine Encephalitis be prevented?

There is an effective Eastern equine encephalitis vaccine for horses and birds, but there is no licensed EEE vaccine for people.

Prevention of EEE transmission requires a coordinated program of monitoring the virus in the vector mosquitoes, as well as effective mosquito surveillance and control activities, and public education regarding personal precautions that can be taken to reduce the risk of mosquito bites. Every year the New Jersey State Mosquito Control Commission (SMCC) funds the Vector Surveillance Program at Rutgers University that monitors EEE in Cs. melanura mosquitoes at study sites in the southern part of the state. Mosquitoes are tested for the virus at the NJ Department of Health and Senior Services Public Health Laboratory. State and county mosquito control agencies follow integrated pest management practices including larval and adult mosquito surveillance, habitat management, biological control, public education and limited use of insecticides. When surveillance results indicate that there is an elevated risk of EEE transmission, the State and county mosquito control agencies are prepared to promptly respond with the most effective larval and adult mosquito control measures, including use of the State Airspray Program of the SMCC to control the salt marsh mosquito in coastal counties and other mosquito vectors in upland areas.

The chance that any one person will become ill with EEE (or West Nile virus) from a mosquito bite is extremely low. Keep in mind that the female salt marsh mosquito, the human vector of EEE, can migrate many miles from the coastal marshes and is an aggressive biter, day or night. You can avoid mosquito bites and reduce your risk in the following ways:

• Apply insect repellent containing up to 30% DEET to exposed skin or clothing when you go outdoors. Do not apply to children under 3 years old, and do not apply to hands or face of children. Carefully follow all label directions.
  
  
• When possible, wear long-sleeved shirts, long pants and socks when outdoors. Clothes may be sprayed with a repellent containing permethrin or DEET, but don’t apply permethrin to the skin and don’t apply DEET to the skin under clothing. Remember that the salt marsh mosquito is a persistent biter at any time of day.
  
  
• Repair or install new screens on doors and windows to keep out mosquitoes.
  
  
• Eliminate all potential mosquito breeding sites around the home. This includes cleaning out gutters and drains, disposing of old tires, draining standing water from pool covers and ditches, removing all containers which hold water, properly maintaining pools and changing birdbath water every several days.
  
  
• For further information about mosquito surveillance and control in the community, contact your county mosquito control agency. As the pesticide applicator, the county agency can answer questions about any insecticide applications which are necessary for mosquito control in the community.

Where can I get more information about EEE?

The pamphlet, Mosquito Borne Viruses of New Jersey and other informational materials are available from your local health department and county mosquito control agency. The following web sites are a source of additional information:

• New Jersey Department of Health and Senior Services (www.state.nj.us/health),
  
  
• New Jersey Department of Environmental Protection (www.state.nj.us/dep/mosquito),
  
  
• New Jersey Mosquito Homepage (www.njmosquito.org),
  
  
• New Jersey Department of Agriculture (www.state.nj.us/agriculture),
  
  
• Centers for Disease Control and Prevention (www.cdc.gov)