Surveillance Results of Japanese Encephalitis Vector Mosquitoes in the Republic of Korea in 2025.

OBJECTIVES

Japanese encephalitis (JE) is a viral infectious disease primarily transmitted by Culex tritaeniorhynchus, with approximately 10-20 human cases reported annually in the Republic of Korea (ROK). The Korea Disease Control and Prevention Agency conducts annual surveillance to monitor vector mosquito occurrence and trends. This study aimed to evaluate the seasonal occurrence and regional distribution patterns of JE vector mosquitoes based on 2025 surveillance data.

METHODS

In 2025, JE vector surveillance was conducted across 64 regions in the ROK. This study analyzed data from 12 provincial Health and Environment Institutes, where black light traps were installed at cattle barns. The trap index (individuals/traps/days) was calculated to compare seasonal patterns and regional differences in Cx. tritaeniorhynchus abundance. In addition, genetic analysis was performed to detect the JE virus in mosquito samples.

RESULTS

A total of 22 mosquito species belonging to 8 genera were identified. The overall trap index was 251.2, with a Cx. tritaeniorhynchus trap index of 67.4. Seasonal occurrence of Cx. tritaeniorhynchus was concentrated between July and September, with a peak in the 36th week. Southern regions showed earlier emergence and higher densities, whereas northern regions showed delayed emergence and lower densities.

CONCLUSIONS

In 2025, the trap index for Cx. tritaeniorhynchus decreased by 34.8% compared to the previous year and by 9.1% relative to the 2022-2024 average year. This reduction was likely associated with climatic conditions, including a higher-than-normal summer mean temperature (25.7°C; +2.0°C above normal) and heavy rainfall in mid-July (200-700 mm), which may have affected mosquito survival and breeding. Continuous and high-resolution surveillance is essential for effective JE prevention, particularly in the context of climate change.