Multi-site surveillance of the severe fever with thrombocytopenia syndrome virus vector Haemaphysalis longicornis across diverse locations in Korea and evaluation of cinnamaldehyde-derived vector-control agents

This study comprises two distinct but parallel investigations concerning Haemaphysalis longicornis in Korea: an exploratory ecological survey of vector density across 20 sites in 2023 and a laboratory-based screening of Cinnamomum cassia oils, cinnamaldehyde-derived compounds, and associated enzymatic responses in H. longicornis. In the ecological survey, H. longicornis accounted for 75.5% of > 10,000 vectors, consistent with its role as the principal vector of severe fever with thrombocytopenia syndrome virus (SFTSV). Generalized linear models indicated that mean temperature (β=0.46, p < 0.001) and vegetation type (β=0.38, p = 0.003) were associated with variation in site-level vector density. Because the dataset represents a single-season, site-level survey without SFTSV detection, the spatial outputs reflect relative exposure opportunity rather than epidemiological transmission risk. In the parallel laboratory investigation, immersion bioassays evaluated C. cassia oils and cinnamaldehyde-derived compounds across life stages, alongside acetylcholinesterase (AChE) and detoxification enzymes. Indian oil (cinnamaldehyde 89.42%) yielded LC₅₀ values of 3.82, 8.13, and 17.49 μg/mL for larvae, nymphs, and adults, with lower LC₅₀ values than diethyltoluamide. Structure-activity analyses indicated that α-methylcinnamaldehyde was among the derivatives with the numerically lowest LC₅₀ values (1.89/4.76/9.56 μg/mL), interpreted as descriptive outcomes rather than potency rankings. Cinnamaldehyde inhibited AChE in vitro and in vivo, while ECOD and α-/β-esterase activities decreased and glutathione S-transferase remained unchanged, indicating an acute generalized stress response and/or direct suppression of detoxification enzymes rather than upregulation of resistance-related detoxification pathways. These parallel investigations provide ecological context and laboratory evidence but remain independent; laboratory results cannot be extrapolated to field performance across the surveillance.