Japanese encephalitis

1 Active Outbreak

Japanese encephalitis (JE) is a serious viral infection of the brain caused by the Japanese encephalitis virus (JEV). It primarily affects children and is the leading cause of viral encephalitis in many parts of Asia. The virus is transmitted to humans through mosquito bites.

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231d ago
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What is Japanese encephalitis?

Japanese encephalitis was first recognized as a distinct clinical entity in Japan in the 1870s, and the causative virus was isolated in 1935. It became a major public health concern across Asia due to recurrent large-scale outbreaks. The development and widespread use of effective vaccines in the mid-20th century significantly reduced its burden in many endemic regions.

Symptoms

  • Most infections are *asymptomatic* or cause mild, flu-like symptoms (fever, headache).
  • Severe disease begins with sudden high fever, headache, nausea, and vomiting.
  • Progresses to neurological symptoms: altered mental status, disorientation, tremors, rigidity, seizures (especially in children), and paralysis.
  • Can lead to coma and death, with significant long-term neurological and psychiatric sequelae in survivors.

Transmission

Japanese encephalitis is transmitted to humans through the bites of infected *Culex* mosquitoes, primarily *Culex tritaeniorhynchus*. These mosquitoes acquire the virus by feeding on infected birds (such as herons and egrets) and pigs, which act as amplifying hosts. Humans are dead-end hosts, meaning they do not transmit the virus to mosquitoes or other humans.

Contagious Period: Varies by disease

Prevention

  • Vaccination: Highly effective vaccines are available and recommended for people living in or traveling to endemic areas.
  • Mosquito bite prevention: Use insect repellent containing DEET, picaridin, or IR3535; wear long sleeves and pants; use mosquito nets over beds.
  • Environmental control: Eliminate mosquito breeding sites by draining standing water around homes and communities.

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🚨 Safety guidelines urged after year's first case of Japenese encaphalitis

United States, Alaska 2025-10-14
Active

The first case of Japanese encephalitis this year has been reported, prompting authorities to urge the public to follow safety guidelines. This emphasizes the need for immediate preventive measures against this serious mosquito-borne disease.

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Expert Resources & References

Trusted information from leading health organizations

CDC

Official guidance from the U.S. Centers for Disease Control and Prevention

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WHO

Global disease surveillance and guidelines from the World Health Organization

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Research

Latest peer-reviewed research and clinical studies

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Medically Reviewed Content

Disease information on Virus Watcher is reviewed by our Chief Epidemiologist, a former CDC lead analyst for FluSight forecasting. Outbreak data is aggregated from verified sources including BEACON, ProMED, WHO, CDC, and 50+ national health agencies. This information is for educational purposes and should not replace professional medical advice.

Last reviewed: 2026-06-03

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