Field evaluation of personal protection methods against outdoor-biting mosquitoes in Lao PDR.

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.