Health authorities confirmed the first domestic case of Japanese encephalitis for the year in a woman in her 60s presenting with a fever of 39.1°C, chills, and vomiting, according to the Korea Disease Control and Prevention Agency (KDCA). The patient, who has underlying conditions including chronic renal failure, sought medical care on Aug. 15 and remains hospitalized while investigators confirm she had no history of vaccination and a verified history of mosquito bites.
Diagnostic Confirmation and Patient Status
Diagnostic testing by the KDCA on Sept. 9 confirmed the infection after laboratory results showed a more than fourfold increase in antibody titers in convalescent-phase serum compared to the acute phase, as reported by the agency. The patient first visited a medical institution on Aug. 15 with acute symptoms including a 39.1°C fever, chills, and vomiting. Epidemiological investigators established that she had not received a Japanese encephalitis vaccine and suffered mosquito bites prior to symptom onset. She is currently receiving inpatient treatment for the viral illness alongside management for underlying chronic kidney disease.
Seasonal Trends and Vector Surveillance
The KDCA notes that approximately 80 percent of domestic Japanese encephalitis cases in South Korea occur between September and October, with the broader transmission season running from August to November. Individuals aged 50 and older account for 65.9 percent of all recorded cases. The primary vector, the Culex tritaeniorhynchus mosquito, is a small, dark-brown insect that feeds primarily at night and remains active from April through October. Surveillance data for early September, covering Week 36 from Aug. 30 to Sept. 5, detected an average mosquito count of 121, according to agency figures. This count falls below the three-year average of 381 and last year’s count of 561 for the same period, though health officials stress that continued vector activity warrants vigilance throughout the autumn peak.
Pro Tip: Health authorities advise the public to avoid outdoor activities near high-risk environments like rice paddies and pig farms during nighttime hours when the Culex tritaeniorhynchus mosquito is most active. Use EPA-registered insect repellents and wear long-sleeved clothing to reduce bite risks.
Clinical Risks and Complications
While most people infected with the Japanese encephalitis virus remain asymptomatic or experience only mild effects such as fever and headache, rare cases progress to severe encephalitis. According to KDCA data, progressive disease causes high fever, seizures, neck stiffness, confusion, convulsions, and paralysis, carrying a mortality rate of 20 to 30 percent. Furthermore, 30 to 50 percent of patients who develop encephalitis suffer lasting neurological complications depending on the specific area of brain damage. Prompt medical diagnosis is critical when acute symptoms appear during the peak transmission months.
Vaccination Guidelines and Recommendations
Preventive vaccination is available through both national programs and individual-pay options. KDCA Commissioner Lim Seung-gwan urged eligible individuals to follow standard immunization schedules amid rising vector numbers and the onset of peak seasonal cases. Children aged 12 and under, specifically those born on or after Jan. 1, 2013, are eligible for the National Immunization Program. The inactivated vaccine requires five doses starting at 12 to 23 months of age, while the live attenuated vaccine requires two doses over the same timeframe, as outlined by health authorities.
Additionally, vaccination at the individual’s expense is recommended for previously unvaccinated adults aged 18 and older who fall into specific risk groups, according to the KDCA. These groups include:
- Residents of high-risk areas, such as locations near rice paddies or pig farms, or individuals planning activities in those areas during the transmission season.
- Foreign nationals moving from non-endemic regions for long-term residence in South Korea.
- Travelers visiting countries where Japanese encephalitis is endemic, including Australia, Bangladesh, Bhutan, Brunei, Cambodia, China, India, Indonesia, Japan, Laos, Malaysia, Myanmar, Nepal, North Korea, Pakistan, Papua New Guinea, the Philippines, Russia, Singapore, Sri Lanka, Taiwan, Thailand, Timor-Leste, and Vietnam.
Did You Know? South Korea previously recorded seven cases with zero deaths last year, following 21 cases and six deaths during the 2024 season, according to historical KDCA surveillance tracking.
Frequently Asked Questions
What are the primary symptoms of Japanese encephalitis?
Initial infection often causes no symptoms or mild signs like fever and headache. Severe cases progress to encephalitis, featuring high fever, seizures, neck stiffness, confusion, convulsions, and paralysis.
When is the peak period for Japanese encephalitis in Korea?
According to the KDCA, roughly 80 percent of domestic cases occur during September and October, within a broader seasonal window spanning August through November.
Who should get vaccinated against Japanese encephalitis?
Vaccination is standard for children aged 12 and under under the National Immunization Program. It is also recommended for unvaccinated adults aged 18 and older living near rice paddies or pig farms, long-term foreign residents, and travelers to endemic countries.
Which mosquito transmits the Japanese encephalitis virus?
The primary vector is the Culex tritaeniorhynchus mosquito, a small, dark-brown insect that feeds at night and remains active in Korea from April to October.
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