Upward shift of breeding sites to the remote forest streams and spatial distribution of Anopheles mosquitoes in Korea, 2022

Abstract Background Limited information is available regarding the characterization of the current Anopheles breeding site in Korea, although malaria is still endemic. Methods Here, we explored Anopheline adults and breeding sites at three villages (WL, Wollong-myeon; PJ, Paju-eup; MS, Munsan-eup) at Goyang city and two villages (HS, Haseong-myeon; WG, Wolgot-myeon) at Gimpo near the demilitarized zone (DMZ) in Gyeonggi-do province, Korea from May to September 2022. Besides, a natural environmental factor associated with the seasonal abundance of Anopheles larvae was recently identified. Light traps were used to monitor mosquitos in the field in villages where P. vivax malaria cases had previously been reported. Anopheles mosquito adults were used to determine species of mosquito adults by polymerase chain reaction sequencing. Collected larvae were cultured at different concentrations of dissolved oxygen (DO) to investigate the effect of DO on larvae development. Results Anopheles sinensis was the most prevalent spp, showing that An. sinensis, An. pullus, An. sineroides, An. belenrae, and An. lidesayi accounted for 41.67% (33/60), 1.67% (1/60), 3.33% (2/60), 5.00% (3/60), 3.33% (2/60), respectively, (each mosquito spp./total Anopheles adult) at WG. New breeding site of Anopheles larvae was found in a forest stream at WG and associated with the forest environment. The Anopheline mosquito larvae distribution to deeper forest zone (< 100 m from human residence) and the upward shift in the most remote littoral area of the forest stream was found in Korea. Notably, the DO was significantly higher in the forest stream than in the tap water, showing 8.45 ± 0.11 and 9.7 ± 0.17 (mean ± SD) mg/L of DO, respectively, and it was confirmed in vitro culture, implying the relevance of DO in Anopheles larvae growth. Conclusions This study suggests the potential retreat of Anopheline mosquito larvae distribution to deeper forest zone and thus, the implementation of control measures in forest areas across the DMZ area may be requested to eradicate malaria vectors in Korea.