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

Published: 14 Oct. 2025, 20:07

Quarantine workers conduct mosquito lava extermination in Suwon, Gyeonggi on Sept. 25. [NEWS1]

With Korea’s first confirmed case of Japanese encephalitis this year, disease control authorities are urging the public to follow prevention guidelines and complete vaccination.

A man in his 30s was diagnosed with Japanese encephalitis on Tuesday, nearly a month after visiting a hospital with symptoms, according to the Korea Disease Control and Prevention Agency (KDCA) on Tuesday.

The patient had reported a high fever over 39 degrees Celsius (102.2 degrees Fahrenheit), chills, headache and nausea when he sought medical care on Sept. 16. He is currently hospitalized in a reduced state of consciousness.

A KDCA official explained that while the virus was not detected in early testing — as the patient had not visited a hospital during the acute phase — antibody tests performed during recovery showed a more than fourfold increase in antibodies, confirming the diagnosis.

An epidemiological investigation found that the patient was bitten by mosquitoes while camping and had not been vaccinated against Japanese encephalitis.

Most domestic cases of Japanese encephalitis occur between August and November, with about 80 percent concentrated in September and October. This year's first case was reported later than usual — about six weeks later than the average over the past decade.

Culex tritaeniorhynchus, a small, dark brown mosquito that is active at night, a primary vector for Japanese encephalitis [KOREA DISEASE CONTROL AND PREVENTION AGENCY]

“The delayed onset may be due to this summer’s unusually hot weather, which reduced the mosquito population,” a KDCA official said.

Adults in their 50s or older account for 87.9 percent of cases. Japanese encephalitis can cause mild symptoms like fever and headache, but in rare cases progresses to encephalitis, leading to severe symptoms such as high fever, seizures, neck stiffness, confusion, convulsions and paralysis.

Between 20 and 30 percent of those who develop encephalitis may die, while 30 to 50 percent suffer long-term neurological complications depending on the areas affected. The KDCA emphasized the importance of early diagnosis and treatment due to the risk of lasting aftereffects.

The primary vector for the disease is the Culex tritaeniorhynchus, a small, dark brown mosquito that is active at night. It typically breeds in rice paddies, animal pens and puddles and has been observed across the country through October.

Quarantine workers conduct mosquito lava extermination in Suwon, Gyeonggi on Sept. 25. [NEWS1]

As of the end of September, or the 39th week of the year, mosquito surveillance showed an average of 108 mosquitoes per trap, indicating persistent activity and a continued risk of bites. The KDCA recommends avoiding outdoor activities from dusk to dawn between April and October, when the vector is active.

Japanese encephalitis is preventable through vaccination. Children underage 12, born after January 2012, are eligible for free national immunization and are advised to complete the standard vaccination schedule.

Adults who have never been vaccinated and either live near rice fields or pig farms or plan to travel to high-risk countries such as Japan, Australia, Bangladesh, China or India are also advised to get vaccinated.

“Mosquito activity is rising again, and October marks the period when most cases are reported,” said KDCA Commissioner Lim Seung-kwan. “We urge people to follow prevention guidelines to avoid mosquito bites and to complete their vaccinations if eligible.”

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.
BY CHAE HYE-SEON [[email protected]]