Protective efficacy and user acceptability of DEET and Vetiver essential oil repellents against Anopheles dirus (Diptera: Culicidae): semi-field and community-based evaluations.

Topical repellents are considered as valuable supplementary tools for reducing vector-borne disease transmission risk by preventing mosquito bites. Plant-based formulations have attracted growing interest as safer, more acceptable alternatives to synthetic repellents, yet evidence for their real-world effectiveness remains limited. This study evaluated the protective efficacy of two topical repellents, DEET and Vetiver essential oil (Vetiver E.O.) against Anopheles dirus Peyton & Harrison, a main malaria vector species, through semi-field system (SFS) trials. These tests were followed by a nine-month community-level randomized trial in Khun Han District, Sisaket Province, with concurrent social science evaluation. In the SFS trials, DEET reduced mosquito landing by 95.75% over 6 h, while Vetiver E.O. conferred moderate protection at 51.9%. Both products also reduced the percentage of blood-feeding, suggesting additional transmission-reducing potential beyond simple landing deterrence. At the community level, 457 participants were randomized into DEET, Vetiver E.O., and placebo groups. DEET participants demonstrated substantially higher product collection adherence and frequency of use than Vetiver E.O. or placebo participants. Participant-reported efficacy and acceptability ratings for Vetiver E.O. were comparable to the placebo group, suggesting that its biological activity was insufficient to generate a perceptible benefit under field conditions. Across all groups, participants predominantly applied repellents to clothing rather than exposed skin, likely attenuating real-world protective efficacy. These findings support the establishment of a minimum efficacy threshold under semi-field conditions before proceeding to community trials with candidate repellents and underscore the need to implement personal protection strategies that minimize the need for regular application by each individual.