Japanese encephalitis is the leading cause of viral encephalitis in Asia with 30-50,000 cases reported annually. Fewer than 1 case/year is reported in U.S. civilians and military personnel traveling to and living in Asia. Rare outbreaks in U.S. territories in Western Pacific have occurred.

Causes

Japanese Encephalitis is transmitted by rice field breeding mosquitoes (primarily the Culex tritaeniorhynchus group) that become infected with Japanese encephalitis virus (a flavivirus antigenically related to St. Louis encephalitis virus). The lifecycle usually goes like this. Mosquitoes become infected by feeding on domestic pigs and wild birds infected with the Japanese encephalitis virus. Infected mosquitoes then transmit the Japanese encephalitis virus to humans and animals during the feeding process. The Japanese encephalitis virus is amplified in the blood systems of domestic pigs and wild birds. Japanese encephalitis virus is NOT transmitted from person-to-person. Only domestic pigs and wild birds are carriers of the Japanese encephalitis virus.

Risk Factors

Residents of rural areas in endemic locations, active duty military deployed to endemic areas, and expatriates who visit rural areas. Japanese encephalitis does not usually occur in urban areas.

Symptoms

Mild infections occur without apparent symptoms other than fever with headache usually 5 to 15 days after being bitten.. More severe infection is marked by quick onset, headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions (especially in infants) and spastic (but rarely flaccid) paralysis. Case-fatality rates range from 0.3% to 60%.

Diagnosis

Performed by doctor.

Treatment

There is no specific therapy. Intensive supportive therapy is indicated.

Prevention

Japanese encephalitis vaccines are available.

References

CDC