The Human-Baited Double Net Trap: An Alternative to Human Landing Catches for Collecting Outdoor Biting Mosquitoes in Lao PDR

Abstract

Estimating the exposure of individuals to mosquito-borne diseases is a key measure used to evaluate the success of vector control operations. The gold standard is to use human landing catches where mosquitoes are collected off the exposed limbs of human collectors. This is however an unsatisfactory method since it potentially exposes individuals to a range of mosquito-borne diseases. In this study several sampling methods were compared to find a method that is representative of the human-biting rate outdoors, but which does not expose collectors to mosquito-borne infections. The sampling efficiency of four odour-baited traps were compared outdoors in rural Lao PDR; the human-baited double net (HDN) trap, CDC light trap, BG sentinel trap and Suna trap. Subsequently the HDN, the best performing trap, was compared directly with human landing catches (HLC), the ‘gold standard’, for estimating human-biting rates. HDNs collected 11–44 times more mosquitoes than the other traps, with the exception of the HLC. The HDN collected similar numbers of Anopheles (Rate Ratio, RR = 1.16, 95% Confidence Intervals, 95% CI = 0.61–2.20) and Culex mosquitoes (RR = 1.26, 95% CI = 0.74–2.17) as HLC, but under-estimated the numbers of Aedes albopictus (RR = 0.45, 95% CI = 0.27–0.77). Simpson’s index of diversity was 0.845 (95% CI 0.836–0.854) for the HDN trap and 0.778 (95% CI 0.769–0.787) for HLC, indicating that the HDN collected a greater diversity of mosquito species than HLC. Both HLC and HDN can distinguish between low and high biting rates and are crude ways to measure human-biting rate. The HDN is a simple and cheap method to estimate the human-biting rate outdoors without exposing collectors to mosquito bites.

How often do mosquitoes bite humans in southern England? A standardised summer trial at four sites reveals spatial, temporal and site-related variation in biting rates

“…Temporal and spatial variation in mosquito biting rates within an environment can significantly impact the risk of human infection with a mosquito-borne pathogen [15]. Although recent evidence suggests that some artificial trapping approaches are able to sample certain mosquito species at a comparable rate to that of human-baited collections [16–18], the standardised human landing catch remains a valuable method for assessing true biting rates on human hosts. The use of human landing catch techniques is particularly useful in areas where pathogen transmission is not considered to occur, as experiments can proceed without exposing personnel to an increased risk of infection [1].…”

Comparison of the human-baited double net trap with the human landing catch for Aedes albopictus monitoring in Shanghai, China

“…Human landing catches estimate the human-biting rate, which is needed to assess the mosquito-borne disease risk [15]. Given the inherent risk of conducting HLCs in areas where mosquitoes transmit harmful or deadly infections to humans, alternative traps with or without attractants have been developed, such as non-attractant traps [16–18], light-trap with or without carbon dioxide (CO 2 ) [19, 20], and net traps with or without human- or animal-bait [4, 14, 15]. Due to different mosquito species composition or different monitoring scheme designs like variable sampling duration, the results of these trials can vary substantially.…”

“…Often a single door-like opening was used [23], sometimes one or more sides of the net were partly rolled up and pinned or tucked into place, or a horizontal slit was made [10, 24]. Alternatively, the entire net can be raised a few cm from the ground [15]. The outer net used in this study was raised 30 cm from the ground to give access to hungry mosquitoes.…”

“…Rubio-Palis & Curtis [6] and Le Goff et al [7] discarded HDN traps because of their poor efficiency in the collection of anophelines compared with HLCs. For Aedes species, the trial in Lao PDR by Tangenaet al [15] showed that HDN trapped similar numbers of Anopheles and Culex mosquitoes as HLC and about 0.47 times as many as HLC for Ae. albopictus .…”

“…It was mentioned in other HDN tests that human-baits get out of the inner net and perform collection of mosquitoes trapped between the nets at the end of each hour [15]. Such behaviour could put the human-baits under potential biting-risk when performing mosquito collection without protection, even if the collection time is short.…”