Semi-field evaluation of human landing catches versus human double net trap for estimating human biting rate of Anopheles minimus and Anopheles harrisoni in Thailand

Abstract

Background Whilst the human landing catch (HLC) technique is considered the ‘gold standard’ for estimating human-biting rates, it is labor-intensive and fraught with potential risk of exposure to infectious mosquito bites. This study evaluated the feasibility and performance of an alternative method, the human double net trap (HDNT) relative to HLC for monitoring host-seeking malaria vectors of the Anopheles minimus complex in a semi-field system (SFS). Methods HDNT and HLC were positioned in two rooms, 30 m apart at both ends of the SFS. Two human volunteers were rotated between both traps and collected released mosquitoes (n = 100) from 6:00 pm till 6:00 am. Differences in Anopheles mosquito densities among the trapping methods were compared using a generalized linear model based on a negative binomial distribution. Results There were 82.80% (2,136/2,580) of recaptures of wild-caught and 94.50% (2,835/3,000) of laboratory-reared mosquitoes that were molecularly identified as An. harrisoni and An. minimus, respectively. Mean density of An. harrisoni was significantly lower in HNDT (15.50 per night, 95% CI [12.48–18.52]) relative to HLC (25.32 per night (95% CI [22.28–28.36]), p < 0.001). Similarly, the mean density of a laboratory strain of An. minimus recaptured in HDNT was significantly lower (37.87 per night, 95% CI [34.62–41.11]) relative to HLC (56.40 per night, 95% CI [55.37–57.43]), p < 0.001. Relative sampling efficiency analysis showed that HLC was the more efficient trap in collecting the An. minimus complex in the SFS. Conclusion HDNT caught proportionately fewer An. minimus complex than HLC. HDNT was not sensitive nor significantly correlated with HLC, suggesting that it is not an alternative method to HLC.

A semi-field evaluation in Thailand of the use of human landing catches (HLC) versus human-baited double net trap (HDN) for assessing the impact of a volatile pyrethroid spatial repellent and pyrethroid-treated clothing on Anopheles minimus landing

“…KU’s An. minimus laboratory (L) strain is originally from Rong Klang district, Prae province, Thailand, and has been reared at KU’s insectary for the purpose of SFS studies since 1993 [ 22 ]. For this study, female An.…”

“…Also, a field study in Malaysia for evaluating the trapping densities of the HDN (and other trap types) compared to the HLC found that the HDN collected significantly less Anopheles than the HLC [ 21 ]. Further, in Thailand, a recent SFS evaluation of the performance of the HDN compared to the HLC for monitoring Anopheles minimus complex showed that the HDN captured significantly fewer mosquitoes than the HLC, indicating that the HDN might not be a suitable alternative to the HLC in this context [ 22 ]. Given this conflicting body of evidence on the suitability of the HDN as an alternative to the HLC, additional HDN evaluations are needed to help bring clarity around use of the HDN as a trap alternative to the HLC.…”

Field evaluation of a volatile pyrethroid spatial repellent and etofenprox-treated clothing for outdoor protection against forest malaria vectors in Cambodia

“…ITCs primarily protect humans from mosquito bites through contact irritancy (also referred to as contact excito-repellency), some short-range non-contact excitorepellency, feeding inhibition, and mortality [15][16][17]. VPSRs have been extensively evaluated in Africa [18][19][20][21][22][23][24] and increasingly in Southeast Asia [25][26][27][28][29]. ITCs, treated with pyrethroids, have been widely evaluated and show promise for their use against Anopheles biting amongst mobile populations and military/ranger personnel [30][31][32][33].…”

Evaluating human landing catches as a measure of mosquito biting and the importance of considering additional modes of action

“…Here, mosquitoes are captured from the lower limbs of a human volunteer as they land, but before they bite. HLC is a direct measurement of human-vector contact that has not been reproduced accurately using traps [3][4][5], but it has disadvantages especially with wild-field mosquitoes, as pathogen transmission could occur [5]. There is some experimental evidence that HLCs provide a reasonable proxy of human biting [6,7].…”