Comparison between the human landing catch (HLC), an exposure-free mosquito-electrocuting trap (MET) and a BG-Sentinel trap (BGS) for evaluation of transfluthrin emanator against Aedes aegypti using choice and no-choice tests in a semi-field system

Abstract

Background The human landing catch (HLC) measures human exposure to mosquito bites and evaluates the efficacy of vector control tools. However, it may expose volunteers to potentially infected mosquitoes. The mosquito electrocuting trap (MET) and BG-Sentinel traps (BGS) represent alternative, exposure-free methods for sampling host-seeking mosquitoes. This study investigates whether these methods can be effectively used as alternatives to HLC for measuring the efficacy transfluthrin against Aedes aegypti. Methods The protective efficacy (PE) of freestanding passive transfluthrin emanators (FTPEs), measured by HLC, MET and BGS were compared in no-choice and choice tests. The methods were located 2 m from an experimental hut with FTPEs positioned 3 m on either side of them. For the choice experiment, a competitor HLC was included 10 m from the first collection point. One hundred laboratory-reared Ae. aegypti mosquitoes were released and collected for three consecutive hours. Results In the no-choice test, each method measured similar PE; HLC: 66% (95% confidence interval [CI]: 50–82), MET: 55% (95% CI: 48–63) and BGS: 64% (95% CI: 54–73). The proportion of mosquitoes recaptured was consistent between methods (20–24%) in treatment and varied (47–71%) in the control. However, in choice tests, the PE measured by each method varied; HLC: 37% (95% CI: 25–50%), MET: 76% (95% CI: 61–92) and BGS trap: 0% (95% CI: 0–100). Recaptured mosquitoes were no longer consistent between methods in treatment (2–26%) and remained variable in the control (7–42%). FTPE provided 50% PE to the second HLC 10 m away. In the control, the MET and the BGS were less efficacious in collecting mosquitoes in the presence of a second HLC. Conclusions Measurement of the PE in isolation was fairly consistent for HLC, MET and BGS. Because HLC is not advisable, it is reasonable to use MET / BGS as a proxy for HLC for testing VP in areas of active arboviruses endemic areas. The presence of a human host in close proximity invalidated the PE estimates from BGS and METs. Findings also indicated that transfluthrin can protect multiple people in the peridomestic area and that at short-range mosquitoes select humans over the BGS.