Japanese Encephalitis Alert: Korea Issues Nationwide Warning

South Korea is on alert for Japanese encephalitis (JE) following the detection of Culex tritaeniorhynchus mosquitoes – the primary vectors of the virus – in Jeju Special Self-Governing Province and Jeollanam-do. The Korea Disease Control and Prevention Agency (KDCA) issued a nationwide advisory on March 27, 2025, urging citizens to take preventative measures.

What is Japanese Encephalitis?

Japanese encephalitis is a mosquito-borne viral infection that can cause inflammation of the brain. It is prevalent in many parts of Asia and the Western Pacific. While many infections are mild or asymptomatic, severe cases can lead to serious neurological complications and even death.

Early Detection and Rising Temperatures

The detection of the mosquitoes occurred three days earlier than in 2024, on March 30th, indicating a potential acceleration of mosquito activity due to rising temperatures. The average temperature in Jeju and Wando areas was 6.2 degrees Celsius higher compared to the previous year. The KDCA began surveillance on March 16th, a week earlier than the previous year, in response to these changing climate patterns.

Symptoms and Severity

Initial symptoms of Japanese encephalitis typically include fever, headache and vomiting. Though, in rare cases, the infection can progress to encephalitis, causing more severe symptoms such as seizures, convulsions, paralysis, and disorientation. The fatality rate for severe cases ranges from 20% to 30%, and 30% to 50% of those who recover may experience long-term neurological damage.

First Case of 2025

Korea’s first confirmed case of Japanese encephalitis in 2025 involved a man in his 30s diagnosed on October 14, 2025, nearly a month after seeking medical care for symptoms including a high fever (over 39 degrees Celsius), chills, headache, and nausea. The patient had been camping and was not vaccinated against the disease.

Prevention and Vaccination

Currently, there is no specific cure for Japanese encephalitis, making prevention crucial. The KDCA recommends the following preventative measures:

• Avoid outdoor activities from sunset to sunrise (April–October), when mosquitoes are most active.
• Wear long, loose, and light-colored clothing when outdoors at night.
• Apply mosquito repellent to exposed skin, and clothing.
• Avoid strong-scented perfumes or cosmetics.
• Ensure doors and windows have screens, and use mosquito nets indoors.
• Eliminate standing water around the home to prevent mosquito breeding.

Vaccination is available and recommended. Children eligible for national vaccination (born after 2013) should receive the vaccine according to the standard schedule. Adults over 18 who have not been previously vaccinated are advised to consider vaccination, particularly those living or working in high-risk areas (near rice fields and pig farms), long-term foreign residents, and travelers to JE-risk regions.

Key Takeaways

• Korea is experiencing a heightened risk of Japanese encephalitis due to early detection of vector mosquitoes.
• Symptoms range from mild to severe neurological complications.
• Vaccination and mosquito bite prevention are the most effective protective measures.