Encephalitis, an inflammation of the brain, is rare but can be caused by many different viruses. They include:
- Herpes viruses, which include herpes simplex virus, Epstein-Barr virus, and varicella-zoster virus.
- Arboviruses, which are transmitted by blood-sucking insects such as mosquitoes. In the U.S., mosquito-borne encephalitis types include West Nile encephalitis, Eastern equine encephalitis, Western equine encephalitis, St. Louis encephalitis, La Crosse encephalitis.
- Enteroviruses, which are various viruses that enter the body through the gastrointestinal tract.
- Rabies virus, which is transmitted from the saliva of an infected animal.
- Viruses that cause childhood infections, such as rubella, measles, and mumps.
Encephalitis symptoms can appear within 2 days to 2 weeks of exposure to the virus. In milder cases, symptoms resemble the flu. In severe cases of encephalitis, symptoms may include:
- Lethargy and reduced consciousness
- Memory loss
- Stiff neck and back
- Speech, hearing, and vision problems
- Muscle weakness
- Partial paralysis
- Loss of consciousness
Because encephalitis can be dangerous, it needs to be diagnosed promptly. Patients are treated immediately, even before diagnostic tests identify the specific virus that caused the illness. If herpes is a possible cause, the standard treatment is the antiviral drug acyclovir. Once the cause has been determined, other drugs may be administered. Unfortunately, however, many types of encephalitis, such as the ones caused by West Nile virus and other arboviruses, do not respond to antiviral drugs.
The best way to prevent becoming infected with a mosquito-borne virus is to avoid being bitten by a mosquito. Use insect repellant when you go outside, especially during the peak mosquito hours of dusk and dawn. Remove mosquito-breeding environments from your property.
Review Date: 01/26/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.