The Centres for Disease Control light trap (CDC-LT) and the human decoy trap (HDT) compared to the human landing catch (HLC) for measuring Anopheles biting in rural Tanzania

Abstract

Background Vector mosquito biting intensity is an important measure to understand malaria transmission. Human landing catch (HLC) is an effective but labour-intensive, expensive, and potentially hazardous entomological surveillance tool. The Centres for Disease Control light trap (CDC-LT) and the human decoy trap (HDT) are exposure-free alternatives. This study compared the CDC-LT and HDT against HLC for measuring Anopheles biting in rural Tanzania and assessed their suitability as HLC proxies. Methods Indoor mosquito surveys using HLC and CDC-LT and outdoor surveys using HLC and HDT were conducted in 2017 and in 2019 in Ulanga, Tanzania in 19 villages, with one trap/house/night. Species composition, sporozoite rates and density/trap/night were compared. Aggregating the data by village and month, the Bland–Altman approach was used to assess agreement between trap types. Results Overall, 66,807 Anopheles funestus and 14,606 Anopheles arabiensis adult females were caught with 6,013 CDC-LT, 339 indoor-HLC, 136 HDT and 195 outdoor-HLC collections. Indoors, CDC-LT caught fewer An. arabiensis (Adjusted rate ratio [Adj.RR] = 0.35, 95% confidence interval [CI]: 0.27–0.46, p < 0.001) and An. funestus (Adj.RR = 0.63, 95%CI: 0.51–0.79, p < 0.001) than HLC per trap/night. Outdoors, HDT caught fewer An. arabiensis (Adj.RR = 0.04, 95%CI: 0.01–0.14, p < 0.001) and An. funestus (Adj.RR = 0.10, 95%CI: 0.07–0.15, p < 0.001) than HLC. The bias and variability in number of mosquitoes caught by the different traps were dependent on mosquito densities. The relative efficacies of both CDC-LT and HDT in comparison to HLC declined with increased mosquito abundance. The variability in the ratios was substantial for low HLC counts and decreased as mosquito abundance increased. The numbers of sporozoite positive mosquitoes were low for all traps. Conclusions CDC-LT can be suitable for comparing mosquito populations between study arms or over time if accuracy in the absolute biting rate, compared to HLC, is not required. CDC-LT is useful for estimating sporozoite rates because large numbers of traps can be deployed to collect adequate mosquito samples. The present design of the HDT is not amenable for use in large-scale entomological surveys. Use of HLC remains important for estimating human exposure to mosquitoes as part of estimating the entomological inoculation rate (EIR).

CDC light traps underestimate the protective efficacy of an indoor spatial repellent against bites from wild Anopheles arabiensis mosquitoes in Tanzania

“…However, it is clear from this study that it cannot be expected without evidence that CDC-LT, while a ubiquitous and convenient tool, is appropriate for all entomological research questions, including evaluation of spatial repellents. There is a large amount of data that demonstrates that CDC-LT is a valuable tool for measuring the indoor density of host seeking mosquitoes [ 25 , 26 ] but not necessarily human exposure to mosquitoes [ 28 ].…”

“…Nonetheless. it can be labour intensive and taxing on volunteers when done at large scale [ 26 , 49 ], and can be challenging to standardize due to differences in human attractiveness to mosquitoes, skilfulness of collectors, and alertness throughout the collection period [ 25 , 26 ]. Evaluations of the Mosquito Electrocuting Trap (MET) and Biogents Sentinel Trap (BGS) for measurement of the PE of SR using Aedes aegypti have also shown some promise in semi-field experiments if observations are independent because it was observed that mosquitoes divert from traps to nearby humans [ 50 ].…”

“…The CDC light trap (CDC-LT) has been used as a tool to approximate HBR, and a large body of evidence exists on comparing collections of malaria vectors through HLC and CDC-LT [ 24 – 27 ]. The CDC-LT may provide some logistical advantages over HLC in operational settings (ease of use) with no increased risk of exposure of study participants to mosquito bites [ 24 , 25 ] although it does not generally compare directly to HLC [ 25 , 26 , 28 ]. However, it is currently unknown if the CDC-LT is an appropriate tool to measure reductions in the HBR by SR applied indoors i.e., whether the proportional reduction in mosquitoes captured by light traps is a suitable proxy for proportional reductions in blood-feeding or lands.…”

A labor‐saving marking and sampling technique for mark‐release‐recapture research

“…Medical researchers often use correlation and B&A analyses in tandem (Giavarina, 2015). B&A plots have also been used for plant science research (Osorio et al, 2002; Rashidi & Seilsepour, 2009; Yellareddygari & Gudmestad, 2017; Nurfikari & de Boer, 2021; Lipiec & Usowicz, 2021), but rarely for entomological research (Massue et al, 2016; Nurfikari & de Boer, 2021; Namango et al, 2022). A key feature of the B&A difference plot analysis is that, rather than provide an indication of any statistical significance between the methods of assessment, it instead provides a level of agreement and direction of bias between methods for the researcher to use their judgement to decide whether a method's level of bias is acceptable for a given study.…”

PCR–RFLP assays for the identification of Anopheles (Diptera: Culicidae) species circulating in Honduras

“…The mosquitoes were collected in the peridomicile and extradomicile during the night. Two collection methods were used: the Center for Disease Control trap (CDC-LT) [ 41 ] provided with light as an attractant, and aspiration of resting mosquitoes, sometimes complemented by human landing catch. Mosquitoes were separated and stored dry in 1.5 mL tubes and subsequently identified under a stereoscope using morphological keys for female anophelines from Central America and Mexico [ 11 ].…”