Japanese encephalitis


A form of encephalitis caused by a flavivirus (Japanese B encephalitis virus - JBEV) and transmitted by mosquito bites.


* Mild infections have mild symptoms: - Mild symptoms - Fever - Headache * More severe infection symptoms: - Rapid onset - Headache - High fever - Neck stiffness - Stupor - Disorientation - Coma - Tremors - Occasional convulsions (especially in infants) - Spastic paralysis - Flaccid paralysis - rarely * Asymptomatic * Fever * Headache * Nausea * Vomiting * Behavioral changes * Neurological deficits * Stupor * Increased protein level in cerebrospinal fluid


The Japanese encephalitis virus has a complex life cycle involving domestic pigs and a specific type of mosquito, Culex tritaeniorhynchus, that lives in rural rice-growing and pig-farming regions. The mosquito breeds in flooded rice fields, marshes, and standing water around planted fields. The virus can infect humans, most domestic animals, birds, bats, snakes, and frogs. After infection, the virus invades the central nervous system, including the brain and spinal cord.


A vaccine is licensed for use in U.S. travelers to rural areas where the disease is common. The vaccine is recommended only for persons who plan to travel in these areas for 4 weeks or more, except in special circumstances such as an ongoing outbreak of disease. Because of the potential for other mosquito-borne diseases in Asia, all travelers should take steps to avoid mosquito bites. The mosquitoes that transmit Japanese encephalitis feed mainly outside during the cooler hours at dusk and dawn. Travelers should minimize outdoor activities at these times, use mosquito repellent on exposed skin, and stay in air-conditioned or well-screened rooms. Travelers to rural areas should use a bed net and aerosol room insecticides.


Diagnosis is based on tests of blood or spinal fluid.


Mortality rate for Japanese encephalitis: Case-fatality rates range from 0.3% to 60%. (Source: excerpt from Questions and Answers About Japanese Encephalitis: DVBID)


There is no specific treatment for Japanese encephalitis and treatment is supportive. There is no transmission from person to person and therefore patients do not need to be isolated. The use of arctigenin has been shown to be effective in a mouse model of Japanese encephalitis, but there is as yet no clinical evidence to support its use.