Risk is present throughout the country. Outbreaks occur mostly in the northern region (Chiang Mai valley) with sporadic cases reported from the areas of Sukhothai, the suburbs of Bangkok and Phitsanulok, as well as from the southern regions of the country. Transmission occurs all year with seasonal peaks from May to October in northern areas.
Japanese Encephalitis is a viral infection caused by RNA viruses belonging to the Flavivirus genus. It is a zoonosis – an animal disease that can spread to humans – primarily transmitted by evening biting Culex mosquitoes that feed on infected birds, pigs and other mammals passing the infection to humans living and working in rural areas around rice paddies and irrigation systems.
Japanese Encephalitis occurs in Southeast Asia. Long-term travellers, persons involved in outdoor recreational activities or on work assignments going to endemic areas are at risk, especially those visiting rural areas, farms, rice fields and irrigation areas. Children under 15 years of age seem to particularly susceptible to the infection. Outbreaks typically occur during or shortly after the rainy season in temperate regions and year-round in tropical regions (peak transmission during summer months).
The majority of cases are asymptomatic – persons do not exhibit symptoms. Those with symptoms usually get ill 5 to 15 days after exposure to the virus. Symptoms include fever, severe headache, vomiting, diarrhea, and general weakness. Some patients will develop neurological symptoms such as tremors, seizures (especially children), expressionless face, and sudden paralysis which can affect the respiratory system and cause bladder retention problems. Patients may also experience behavioural changes which can be misdiagnosed as psychiatric illness. Japanese Encephalitis can be fatal in 20% to 30% percent of cases and many survivors continue to have long-term neurologic, psychiatric, or cognitive problems. Treatment includes supportive care of symptoms.
Recommended for persons travelling extensively in rural areas, long-term travellers, and persons on work assignments in endemic areas.
The inactivated Vero cell vaccine is available in Canada, the USA and select countries. Booster vaccination is recommended 1-2 years if you are at continued risk of exposure. Live attenuated vaccines are available in Japanese Encephalitis endemic countries where they are given as part of the childhood routine immunization schedule. Discuss your options with a healthcare provider if you can’t finish the vaccination series before departure.
Health risk description last reviewed: September 20, 2016
Country information last updated: September 07, 2017