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Viral encephalitis

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of viral encephalitis.

Alternative Names

West Nile virus

Vaccinations

Certain vaccinations can help prevent the diseases that can lead to encephalitis.

Measles

Measles used to be a very common childhood disease. In about 1 in 1,000 cases it can lead to encephalitis or death. The risk for these severe complications is highest in the very young and very old. Aggressive vaccination programs have reduced the incidence of measles in the U.S. to fewer than 100 cases a year. In very rare cases, encephalopathy (brain damage) associated with the live-measles vaccine has occurred, but the risk is far lower than brain events from the disease itself.

Vaccine for Varicella Virus (Chickenpox and Shingles)

Herpes zoster, or shingles, is a reactivation of the varicella virus, which causes chickenpox. A live-virus vaccine (Varivax) produces persistent immunity against chickenpox. Data show that the vaccine can prevent chickenpox or reduce the severity of the illness even if it is used within 3 days, and possibly up to 5 days, after exposure to the infection. The vaccine is protective in about 85% of cases, and even if a vaccinated person becomes infected, the disease is almost always mild. In spite of some concerns, studies indicate that protection is long lasting. The vaccine is now recommended for all children between the ages of 18 months and adolescence who have not yet had chickenpox.

Vaccine against Flaviviruses (West Nile Virus, Japanese Encephalitis Virus, St. Louis Encephalitis)

Researchers are investigating a number of vaccines against the flavivirus family of arboviruses.

A vaccine (JE-VAX) is currently available for Japanese encephalitis. In travelers, it is only recommended for those visiting rural areas in high-risk Asian countries for more than 30 days. These countries include China, Korea, India and neighboring areas, and Southeast Asia. The disease may occur with lower frequency in Japan, Taiwan, Singapore, Hong Kong, and eastern Russia. A new type of single-dose vaccine (ChimeriVax-JE) is currently in Phase III trials.

Two types of vaccines, chimeric and DNA, are under investigation for West Nile virus, but it will be several years before these vaccines become commercially available. The chimeric type of vaccine combines the genes of several different viruses. Promising results for a Phase I trial of the ChimeriVax-West Nile vaccine, which combines West Nile and yellow fever viruses, were reported in 2005. Also in 2005, the U.S. National Institute of Allergy and Infectious Disease began a small clinical trial of a DNA plasmid WNV vaccine.

Rabies Vaccine

Anyone who is exposed to bats, or is exposed to secretions of an animal suspected of having rabies, should be given the rabies vaccine, whether or not there are indications of rabies. Exposed individuals should also receive immune globulin unless they were previously vaccinated. Veterinarians and animal handlers should be vaccinated. This does not eliminate the need for treatment if they are exposed to rabies, but it reduces the intensity of the treatment. Side effects include:

• Pain
• Redness
• Headache
• Stomach pain
• Nausea
• Dizziness
• Muscle aches
• Swelling at the injection site

Allergic response can occur after the first shot and as long as 21 days after a booster shot. Rare cases of neurological disorders have been reported that cause pain and paralysis in the legs and arms, which clear up in about 12 weeks.

• Review Date: 1/18/2007
• Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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