What causes eastern equine encephalitis?
Eastern equine encephalitis virus (EEEV), a flavivirus, causes eastern equine encephalitis.
How do people get infected with EEEV?
People get eastern equine encephalitis from the bite of an infected mosquito, most commonly Aedes albopictus, Ae. vexans, Coquillettidia perturbans, certain species of Culex, Ochlerotatus canadensis and O. sollicitans (see the Virginia species page to see several species known or suspected of transmitting EEEV to humans). The transmission cycle of the virus between mosquitoes, animals and humans is more complicated than that of other mosquito-borne viral diseases. EEEV is normally passed between birds (the amplification host) and the mosquito, Culiseta melanura (the mosquito vector). C. melanura, however, doesn't normally bite mammals and is not a significant vector of EEEV to humans (but see here for evidence of transmission between C. melanura and humans). The virus is transmitted to humans and other mammals by other species of mosquito (above) called bridge vectors. These bridge vectors get the virus from biting infected birds, then infect mammals, which are "dead-end" hosts. Dead-end hosts do not develop a high enough concentration of virus in their blood to pass the virus back to mosquitoes.
What are the symptoms of EEEV infections?
- Compared to other mosquito-borne forms of encephalitis, few people show no symptoms.
- The mild form of the disease, called systemic EEEV disease, is characterized by fever, chills, joint aches and muscle aches.
- The severe form of the disease, encephalitic EEEV disease, is characterized by fever, headache, mood alterations (restlessness, irritability and drowsiness), digestive symptoms (anorexia, diarrhea and vomiting), convulsions and coma. In infants, the severe symptoms appear quickly; in others, the encephalitis is usually preceded by a period of systemic symptoms.
What is the recovery rate for EEEV infections?
- About one third of all EEEV infections in humans are lethal. This makes eastern equine encephalitis the deadliest of the mosquito-borne viruses in Virginia.
- Full recovery from the systemic infection occurs after about a week or two if no neuroinvasive (encephalitic) symptoms have occurred.
- Many of the survivors of the encephalitic form of the disease have chronic long-term brain dysfunction, which can become progressively more severe.
How is the disease treated? Is there a vaccine?
There is no vaccine and no specific treatment for EEEV infections. Treatments are based on symptoms and focus on relieving pain and discomfort.
Who is most at risk?
Anyone can become infected with EEEV. While infants appear especially susceptible to the encephalitic form of the disease, the causes behind which form of the disease develops is not well understood.
Where in the US have EEEV infections occurred?
EEEV infections have been confirmed in 20 states between 1964 and 2010.
How can I protect myself?
The most effective ways to prevent infection with EEEV is to minimize your exposure to mosquito bites. See the mosquito safety page for more information.
Where can I get more information?
The Centers for Disease Control and Prevention is an excellent source of information. Scientific publications about Eastern equine encephalitis can be obtained through PubMed.gov.