Which trap is best? Alternatives to outdoor human landing catches for malaria vector surveillance: a meta-analysis

Abstract

Background Human landing catches (HLC) are an entomological collection technique in which humans are used as attractants to capture medically relevant host-seeking mosquitoes. The use of this method has been a topic of extensive debate for decades mainly due to ethical concerns. Many alternatives to HLC have been proposed; however, no quantitative review and meta-analysis comparing HLC to outdoor alternative trapping methods has been conducted. Methods A total of 58 comparisons across 12 countries were identified. We conducted a meta-analysis comparing the standardized mean difference of Anopheles captured by HLC and alternative traps. To explain heterogeneity, three moderators were chosen for analysis: trap type, location of study, and species captured. A meta-regression was fit to understand how the linear combination of moderators helped in explaining heterogeneity. The possibility of biased results due to publication bias was also explored. Results Random-effects meta-analysis showed no statistically significant difference in the mean difference of Anopheles collected. Moderator analysis was conducted to determine the effects of trap type, geographical location of study, and the species of Anopheles captured. On average, tent-based traps captured significantly more Anopheles than outdoor HLC (95% CI: [− .9065, − 0.0544]), alternative traps in Africa captured on average more mosquitoes than outdoor HLC (95% CI: [− 2.8750, − 0.0294]), and alternative traps overall captured significantly more Anopheles gambiae s.l. than outdoor HLC (95% CI: [− 4.4613, − 0.2473]) on average. Meta-regression showed that up to 55.77% of the total heterogeneity found can be explained by a linear combination of the three moderators and the interaction between trap type and species. Subset analysis on An. gambiae s.l. showed that light traps specifically captured on average more of this species than HLC (95% CI: [− 18.3751, − 1.0629]). Publication bias likely exists. With 59.65% of studies reporting p-values less than 0.025, we believe there is an over representation in the literature of results indicating that alternative traps are superior to outdoor HLC. Conclusions Currently, there is no consensus on a single “magic bullet” alternative to outdoor HLC. The diversity of many alternative trap comparisons restricts potential metrics for comparisons to outdoor HLC. Further standardization and specific question-driven trap evaluations that consider target vector species and the vector control landscape are needed to allow for robust meta-analyses with less heterogeneity and to develop data-driven decision-making tools for malaria vector surveillance and control.

Impacts of land use type on sampling methods for human and simian malaria vectors

“…Mechanical traps like the CDC Light trap and the BG-Sentinel traps have collected mosquitoes for decades. In sub-Sahara Africa, CDC Light traps and other mechanical traps supplemented or replaced HLCs for malaria vector collections to provide rough estimates of human biting rates, despite their lower sensitivity (42). In Asia, however, mechanical traps have not been as promising.…”

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

“…To date, mosquito landing is the accepted endpoint to evaluate the impact of bite prevention tools on human-vector exposure [ 3 ], measured by the gold standard HLC trapping method. However, a gap exists in the collective repertoire of proven field collection methods other than HLCs to evaluate the impact of interventions that act primarily through non-contact or contact irritancy (spatial repellency) on mosquito landing (i.e., human-vector exposure) [ 12 ]. There are several SFS and field intervention evaluation studies that have evaluated the impact of VPSRs on mosquito landing as a proxy for biting using trapping methods other than the HLC, such as the CDC LT [ 56 – 59 ].…”

“…In response to these challenges, a variety of possible alternative, ‘exposure-free’, collection methods been developed and evaluated against HLCs to examine mosquito landing rate equivalencies under semi-field and field conditions [ 9 – 12 ]. A commonly used alternative trap type is the CDC light trap [ 13 ], which is placed next to a person sleeping under a bed net.…”

Entomological drivers of uneven malaria transmission in urban lowland areas in Bouaké, Côte d’Ivoire

“…Adult mosquitoes were caught by the human landing catching (HLC) method that is still considered the “gold standard” to measure Anopheles vector biting on humans [ 18 ], in inhabited areas located along the two lowlands from February to December 2019 (except in January, April and May due to human resource constraints). For comparison with a recent study in Bouaké [ 11 ], the entomological data were organized by season: dry season (February, March, November and December) and rainy season (June to October).…”