Abstract
BackgroundMosquito sampling methods are essential for monitoring and evaluating malaria vector control interventions. In urban Dar es Salaam, human landing catch (HLC) is the only method sufficiently sensitive for monitoring malaria-transmitting Anopheles. HLC is labour intensive, cumbersome, hazardous, and requires such intense supervision that is difficulty to sustain on large scales.MethodsNovel tent traps were developed as alternatives to HLC. The Furvela tent, designed in Mozambique, incorporates a CDC Light trap (LT) components, while two others from Ifakara, Tanzania (designs A and B) require no electricity or moving parts. Their sensitivity for sampling malaria vectors was compared with LT and HLC over a wide range of vector abundances in rural and urban settings in Tanzania, with endophagic and exophagic populations, respectively, using randomised Latin-square and cross- over experimental designs.ResultsThe sensitivity of LTs was greater than HLC while the opposite was true of Ifakara tent traps (crude mean catch of An. gambiae sensu lato relative to HLC = 0.28, 0.65 and 1.30 for designs A, B and LT in a rural setting and 0.32 for design B in an urban setting). However, Ifakara B catches correlated far better to HLC (r2 = 0.73, P < 0.001) than any other method tested (r2 = 0.04, P = 0.426 and r2 = 0.19, P = 0.006 for Ifakara A and LTs respectively). Only Ifakara B in a rural setting with high vector density exhibited constant sampling efficiency relative to HLC. The relative sensitivity of Ifakara B increased as vector densities decreased in the urban setting and exceeded that of HLC at the lowest densities. None of the tent traps differed from HLC in terms of the proportions of parous mosquitoes (P ≥ 0.849) or An. gambiae s.l. sibling species (P ≥ 0.280) they sampled but both Ifakara A and B designs failed to reduce the proportion of blood-fed mosquitoes caught (Odds ratio [95% Confidence Interval] = 1.6 [1.2, 2.1] and 1.0 [0.8, 1.2], P = 0.002 and 0.998, respectively), probably because of operator exposure while emptying the trap each morning.ConclusionThe Ifakara B trap may have potential for monitoring and evaluating a variety of endophagic and exophagic Afrotropical malaria vectors, particularly at low but epidemiologically relevant population densities. However, operator exposure to mosquito bites remains a concern so additional modifications or protective measures will be required before this design can be considered for widespread, routine use.
Highlights
Mosquito sampling methods are essential for monitoring and evaluating malaria vector control interventions
While Light trap (LT) are relatively reliable [11,12,13,14] and largely unaffected by the presence of insecticidal interventions [15,16], methods which sample indoor-resting mosquitoes [2] are unsuitable for many control programmes because they are adversely affected by the presence of insecticides on nets or walls [17,18] which promote exit [19,20,21] and outdoor resting [22,23,24]
In this article we report the development and evaluation of new tent traps in both rural and urban settings in Tanzania with very different vector population densities and behaviours
Summary
Mosquito sampling methods are essential for monitoring and evaluating malaria vector control interventions. Aside from human landing catch (HLC), the most commonly used methods for sampling host-seeking African malaria vectors are Centers for Disease Control and Prevention miniature light traps (LTs) [5] placed beside occupied bednets. Another major strategy for trapping African malaria vectors exploits the tendency of these endophilic species to rest indoors after blood feeding [6]. While exit traps placed in windows [10] have proven useful for monitoring vector density trends in southern Africa [25] and Equatorial Guinea [26], their efficiency is likely to be influenced by site and timespecific factors such as mosquito and human behaviours, as well as house design. These approaches may be unreliable for estimating representative, consistent and epidemiologically meaningful human-biting rates of vector populations
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