How is JE transmitted?

JE transmission requires a specific ecological triad: Culex tritaeniorhynchus mosquitoes (which breed in irrigated rice fields and stagnant water); pig and wading bird reservoirs (which amplify the virus — developing high-level viraemia without illness); and humans (dead-end hosts — who develop encephalitis but cannot infect mosquitoes back). Transmission peaks during and after the rainy season when mosquito populations surge.

What are the symptoms?

Most JEV infections (over 99%) are asymptomatic or cause mild febrile illness. Of those who develop encephalitis: prodrome of fever, headache, vomiting (2-3 days) → rapidly progressive encephalitis with altered consciousness, seizures, motor deficits, Parkinson-like features, tremors and posturing. High fever persists. Outcome: 20-30% die; 30-50% of survivors have permanent neurological, cognitive or psychiatric sequelae; 20-40% recover fully.

Children under 15 in rural agricultural areas of endemic Asia and the Western Pacific are at highest risk. Adults in endemic areas are often immune from childhood infections. Risk groups outside endemic areas: travellers to rural areas of endemic countries (particularly those spending extended periods in agricultural settings); military personnel in endemic zones. Immunocompromised individuals are at higher risk of severe disease.

What JE vaccines are available?

Several JE vaccines are licensed: SA 14-14-2 (live attenuated — used throughout Asia; single dose; WHO-prequalified; used in Gavi programs; >95% efficacy; cost-effective); IXIARO (inactivated Vero cell-derived — licensed in Europe, US, Australia; 2-dose primary series; primarily for travellers); IC51 (same as IXIARO); JESPECT (IXIARO for Australian market). WHO recommends routine JE vaccination for all people aged ≥9 months in endemic areas.

Is there treatment for JE?

There is no specific antiviral treatment for JE. Management is entirely supportive: control of fever; seizure management (anticonvulsants); management of cerebral oedema; mechanical ventilation if needed; nasogastric feeding; prevention of secondary infections; and intensive nursing care. Early intensive supportive care reduces mortality. Prevention through vaccination is the only effective strategy.

What is the GAVI JE programme?

GAVI approved JE vaccine support in 2013 — enabling Gavi-eligible endemic countries to introduce JE vaccination into their routine immunisation programmes. Multiple countries have since introduced SA 14-14-2 through Gavi support — including India, Nepal, Bangladesh, Cambodia, Laos, Myanmar and the Philippines. Introduction of JE vaccine has dramatically reduced JE incidence in countries that have implemented mass vaccination campaigns.

Can JE spread to new areas?

JE has expanded its geographic range historically — from Japan to much of Asia and the Western Pacific. Climate change may facilitate further expansion — through expansion of Culex mosquito ranges, increased rice cultivation, and changing migratory bird patterns. JE has been detected in northern Australia (for the first time in 2021), suggesting continued range expansion. Europe and the Americas currently do not have the ecological conditions for sustained JE transmission.

How does JE affect travellers?

JE is rare in travellers — but serious when it occurs. Risk depends on: destination (rural endemic areas have higher risk than cities); season (monsoon season higher risk); activities (rural, agricultural, outdoor activities higher risk); and duration (>1 month carries substantially higher risk). WHO recommends JE vaccination for travellers spending ≥1 month in endemic rural areas during transmission season, or for shorter-duration travellers with high-risk itineraries.

How does GMJ News cover Japanese encephalitis?

GMJ News covers WHO JE burden data, GAVI vaccine introduction progress, arbovirus epidemiology and travel health recommendations. JE is part of the GMJ's infectious disease and vaccine-preventable disease coverage — relevant to Georgian healthcare professionals advising travellers to Asia and to PHIG's global health surveillance work.

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Japanese Encephalitis

Q: What is Japanese encephalitis?

Japanese encephalitis (JE) is a mosquito-borne viral infection of the brain caused by Japanese encephalitis virus (JEV) — a flavivirus related to dengue, yellow fever and Zika. It is the leading cause of vaccine-preventable encephalitis in Asia, causing approximately 68,000 clinical cases and 13,600-20,400 deaths per year. Despite its name, JE is now endemic across a much broader region — from Pakistan to the Western Pacific islands.

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

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Japanese encephalitis (JE) — a mosquito-borne viral disease caused by Japanese encephalitis virus (JEV) — is the leading cause of vaccine-preventable encephalitis in Asia: approximately 68,000 clinical cases and 13,600-20,400 deaths occur annually, with survivors often left with severe neurological sequelae (WHO). JE is endemic across 24 countries in South and Southeast Asia and the Western Pacific, primarily affecting rural agricultural communities. Safe and highly effective vaccines (SA 14-14-2 live attenuated; IXIARO inactivated) have been used in national immunisation programmes and, since 2013, are available through Gavi for endemic LMICs.

Key messages

68,000 cases, 13,600 deaths annually

Japanese encephalitis (JE) causes approximately 68,000 clinical cases and 13,600-20,400 deaths per year across 24 endemic countries in Asia and the Western Pacific — the leading cause of vaccine-preventable encephalitis in Asia (WHO).

Severe neurological sequelae

20-30% of JE survivors die; 30-50% of survivors have permanent neurological, cognitive or psychiatric sequelae — including motor deficits, intellectual disability, seizures and behavioural problems. The disability burden is enormous.

Highly effective vaccines

Safe and highly effective JE vaccines — particularly the SA 14-14-2 live attenuated vaccine and IXIARO (inactivated Vero cell-derived) — have dramatically reduced JE incidence in countries that have introduced them. A single dose of SA 14-14-2 provides long-term protection.

Children under 15 most affected

JE predominantly affects children under 15 in rural agricultural areas — where rice fields and pig farming create the vector (Culex tritaeniorhynchus mosquito) breeding and amplifying hosts needed for transmission.

GAVI and Gavi-eligible countries

Since 2013, GAVI has supported JE vaccine introduction in endemic LMICs — enabling many countries to vaccinate children routinely. WHO recommends JE vaccination in all countries with endemic transmission.

Pig reservoir and Culex vector

JE transmission requires three elements: Culex tritaeniorhynchus mosquitoes (breeding in rice fields, feeding on animals); pig and wading bird reservoirs (amplifying hosts for JEV); and dead-end human hosts. Pigs develop high-level viraemia that infects mosquitoes.

Key statistics

68K

clinical JE cases/year

WHO

13-20K

JE deaths/year

WHO

endemic countries

WHO

30-50%

of survivors have permanent neurological sequelae

WHO

<15yr

age of most JE cases in endemic areas

WHO

>99%

vaccine efficacy (SA 14-14-2)

WHO/SAGE

Japanese encephalitis cases reported by country — WHO 2021

Source: WHO. India, China, Thailand, Vietnam and Bangladesh report the highest burdens.

Glossary of key terms

Japanese encephalitis virus (JEV)
WHOA flavivirus (same family as dengue, yellow fever, Zika) — transmitted by Culex tritaeniorhynchus mosquitoes that feed on pigs and wading birds (amplifying hosts) before biting humans (dead-end hosts). Humans do not develop sufficient viraemia to infect mosquitoes.

Culex tritaeniorhynchus
WHOThe primary JE vector — a Culex mosquito that breeds in stagnant water (especially irrigated rice fields), feeds preferentially on pigs and wading birds, and can fly several kilometres. Peak activity is in the evening and early night.

SA 14-14-2 vaccine
WHO/SAGEA live attenuated JE vaccine — developed in China and used across Asia. A single dose provides over 95% efficacy and long-term (probably lifelong) protection. Cheap, heat-stable, used in Gavi-eligible countries. WHO-prequalified.

IXIARO vaccine
Valneva/WHOAn inactivated Vero cell-derived JE vaccine — approved in Europe, the US and Australia for adults and children aged 2 months+. Primary series of two doses; booster after 1-2 years recommended. Used primarily for travellers to endemic areas.

Acute encephalitis syndrome (AES)
WHOA clinical syndrome of acute onset of fever with neurological manifestations (altered consciousness, seizures, focal deficits) — used as a surveillance case definition. JE is one of many causes of AES; in many endemic settings, <50% of AES cases are confirmed JE.

Pig amplifying host
WHOPigs develop high levels of JEV in the blood (viraemia) without becoming ill — making them the primary amplifying host. Infected mosquitoes feeding on pigs acquire JEV; JEV-infected mosquitoes then infect humans. Pig proximity to human settlements dramatically increases JE risk.