Background: Protecting people outdoors against mosquito-borne diseases is a major challenge. Here we compared commercially available personal protection methods to identify the most effective method for outdoor use in northern Lao PDR.
Methods: From June to August 2016 the protective efficacy of treatments were compared in a secondary forest during the afternoon and a village during the evening. Comparisons were made using a replicated Latin square design between: (i) short permethrin-treated overalls; (ii) long permethrin-treated overalls; (iii) short untreated overalls with para-menthane-3,8-diol (PMD) applied topically; (iv) short permethrin-treated overalls plus PMD applied topically; (v) short untreated overalls with metofluthrin coils in a metal casing worn on a belt; and (vi) long untreated overalls. Short untreated overalls served as the control. Cone tests were conducted on the treated and untreated fabric before and after field experiments. A questionnaire survey was used to measure social acceptability.
Results: Mosquito coils in a metal casing worn on a belt resulted in 92.3% (95% confidence interval, CI: 88.9-94.6%). landing protection from female mosquitoes in the afternoon and 68.8% (95% CI: 41.7-83.3%) protection in the evening compared to short untreated clothing. PMD was protective both when combined with short permethrin-treated overalls (afternoon, 68.2%, 95% CI: 52.6-78.7%; evening, 52.3%, 95% CI: 33.8-65.7%) and when used in combination with short untreated overalls (afternoon, 55.0%, 95% CI: 41.7-65.2%; evening, 25.2%, 95% CI: 9.4-38.2%). Whilst long permethrin-treated overalls were protective (afternoon, 61.1%, 95% CI: 51.4-68.8%; evening, 43.0%, 95% CI: 25.5-56.4%), short permethrin-treated overalls and long untreated overalls were not. Exposure to new permethrin-treated fabric in cone tests resulted in 25.0% (95% CI, 17.8-32.2%) and 26.2% (95% CI 16.7-35.8%) mortality for susceptible Ae. albopictus and susceptible Ae. aegypti, respectively. There was a loss of efficacy of permethrin-treated clothing after use in the field, with 3 min knockdown rates of Ae. albopictus and 1 h knockdown of Ae. aegypti decreasing over time. Participants considered all treatments acceptable.
Conclusions: The portable mosquito coils were highly protective against outdoor biting mosquitoes, although there are safety concerns related to its use. The combination of permethrin-treated clothing and PMD repellent represent an alternative treatment for protection against outdoor-biting mosquitoes.
Keywords: Mosquito coil; Para-menthane-3,8-diol (PMD); Permethrin-treated clothing; Topical repellent.