Japanese encephalitis is a viral disease. It is the leading cause of viral encephalitis in Asia, with up to 50,000 cases reported each year. The death rate among persons with symptoms of Japanese encephalitis is 30%, with another 30% having serious neurological complications. However, the risk for most travelers is very low, with fewer than 1 case per million travelers. However, rates increase for those staying for prolonged periods in areas where Japanese encephalitis is common.
Japanese encephalitis is transmitted by infected mosquitoes. When an infected mosquito bites a human, the virus is transferred. In addition, wading birds and pigs can be infected and also transfer the virus back to mosquitoes when bitten by a mosquito. Japanese encephalitis transmission occurs mainly in agricultural and rural areas, especially during summer and fall when conditions result in large amounts of standing water.
Most human infections with Japanese encephalitis do not have symptoms. However, a small percentage of those infected develop a sudden fever, headache, and vomiting about 5 to 15 days after infection. These symptoms are followed by mental status changes, neurological changes, weakness, and movement disorders. Seizures are also common, especially among children. There is no specific treatment for Japanese encephalitis. Therapy mainly consists of supportive care and management of complications. The primary public health approaches to JE prevention is through vaccination and the use of other protective measures in at-risk populations.
Currently, there is only one Japanese encephalitis vaccine. It
is approved by the FDA for use among persons 2 months of age and older.
Product: Ixiaro® (Inactivated Japanese Encephalitis Vaccine)
Manufacturer: Intercell Biomedical
Year licensed: 2009
* To administer a 0.25 mL dose, expel and discard half of the volume from the 0.5 mL pre-filled syringe by pushing the plunger stopper up to the edge of the red line on the syringe barrel prior to injection.
To administer a 0.25 mL dose, expel and discard half of the
volume from the 0.5 mL pre-filled syringe by pushing the plunger stopper
up to the edge of the red line on the syringe barrel prior to
JE occurs in Asia and parts of the Western Pacific. The risk of infection is highest in rural agricultural areas where rice production and flooding irrigation take place, and large numbers of mosquitoes breed in proximity to pigs and wading birds. Individuals are at an increased risk of JE if they spend lots of time outdoors, especially during the evening; when mosquitos are biting; participate in extensive outdoor activities (e.g., camping, hiking, trekking, biking, fishing, hunting or farming); or stay in accommodations without air conditioning, screens, or bed nets.
In most temperate areas of Asia, JE transmission is seasonal, and substantial epidemics can occur, usually peaking in summer and fall. In the subtropics and tropics, transmission can occur year-round, often intensifying during the rainy season. JE can be prevented with a vaccine, but risk can also be reduced by the use of countermeasures, such as insect repellent, permethrin-treated clothing, and vector avoidance.
Visit the CDC JE webpage to see a geographic distribution of the JE virus.