Information on Japanese Encephalitis
Introduction
Japanese encephalitis is a viral disease spread by mosquitoes from infected animals (usually pigs and wading birds) to humans. Since the mosquito that carries the virus breeds in flooded rice fields and pools of water, most human infections occur in rural, agricultural areas in Asia (although occasional cases have been reported from urban locations). About 50,000 cases are reported each year in Asia. However, only a small number of cases have occurred in travelers.
In its early stages, Japanese encephalitis appears to be a flu-like illness with headache, fever, gastrointestinal symptoms, confusion, and other behavior disturbances. If the illness progresses to inflammation of the brain, up to 30% of cases end in death and half end in permanent disability. There is currently no effective drug treatment for the disease once it sets in – it can only run its course. Nevertheless, it is very important to seek supportive medical treatment.
Pregnant women should discuss with their physicians the advisability of travel to risk areas during transmission seasons, as infection during the first and second trimesters is associated with intrauterine infection and miscarriage.
Japanese encephalitis is the leading cause of encephalitis in Asia, occurring with highest frequency in China, the Korean peninsula, the Indian subcontinent, and SE Asia. It occurs less frequently in Japan, Hong Kong, southeast Russia, Singapore, Taiwan, and parts of Oceania.
Transmission tends to occur seasonally in most areas of Asia. In temperate regions, the transmission season generally extends from May through September. In tropical and subtropical regions, transmission is typically greatest during the rainy season and early dry season (which varies by region). However, in some areas, irrigation may cause transmission to occur throughout the year. Infections among travelers are very rare.
Prevention
Every traveler's first line of defense is to take personal protective measures against mosquitoes. Even if you choose to be vaccinated, the vaccine is not 100% effective. Further, there is still a risk of contracting other mosquito-borne illnesses in Asia. The mosquitoes that transmit Japanese encephalitis feed mainly outdoors during the cooler hours at dusk and dawn. You should avoid being outdoors during these times, wear mosquito repellent containing DEET, and stay in air-conditioned or well-screened rooms. Wear long pants and long-sleeved shirts. Use Permethrine treated mosquito netting.
Vaccination
The risk of becoming infected with Japanese encephalitis during short-term travel (less than 30 days) to urban areas is less than 1 in 1 million. Therefore the decision to vaccinate will depend on the length of stay( > 3-4 weeks), contact with agricultural areas, during transmission season. However, because the illness has the potential to be very serious, vaccination is well worth consideration if you will be at high risk.
Lab workers for whom exposure to JE virus is possible should also consider vaccination.
Travelers over age 55 who are going to risk areas during the transmission season should give special consideration to receiving the vaccine. While all travelers are at equal risk of getting the disease, older travelers may be more susceptible to developing neurological symptoms. There is also a higher fatality rate in the elderly.
Adverse effects of vaccine
About 20% of people (1 in 5) who receive the vaccine experience some pain, redness, and swelling at the injection site. About 20% of people also experience 1 or more mild, systemic side effects, such as fever, headache, dizziness, or muscle pain.
About 0.6% of vaccinees (1 in 167) experience a general rash, itching, or swelling, especially of the extremities, face, lips, and throat. In rare cases, vaccinees may suffer shock or respiratory distress. People who have a history of allergies to thimersol, bee stings or medications appear to have a greater risk for developing these side effects to the vaccine. If you experience any of these symptoms, call your doctor immediately.
Because of the risk of these side effects, you'll be asked to take the following precautions:
- Remain in the office for 30 minutes after vaccination.
- Defer international travel and remain in areas with ready access to medical care for at least 10 days after any dose of JE vaccine.
- There is a rare chance that serious problems or even death could occur after receiving any medicine or vaccine. As with any serious medical problem, if the person has a significant or unusual problem after receiving the vaccine, call a doctor or bring the person to a health care provider promptly.
Schedule
Travelers (both children and adults) should try to allow at least 40 days before departure for the 3-injection vaccination schedule. The full recommended primary series has a 1-week wait between the first and second doses and about a 3-week wait between the second and third doses. Then it takes 10 more days for the vaccine to take full effect.
In cases where time constraints make the recommended schedule impractical, the time period between the second and third doses may be shortened to 1 week. In cases where even this schedule is impossible, your health care provider may recommend that you receive 2 doses, 1 week apart. Although this is less effective than the recommended schedule, it does give some short-term protection in about 80% of recipients.
The exact timing of subsequent booster doses (for example, for long-term residents in risk areas) has not been determined. Some sources recommend waiting at least 2 years after you complete the primary series before getting a booster dose.
Vaccine Prices
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