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A new tent trap for sampling exophagic and endophagic members of the Anopheles gambiae complex

Nicodemus J Govella1234*, Prosper P Chaki1234, Yvonne Geissbuhler15, Khadija Kannady2, Fredros Okumu1, J Derek Charlwood6, Robert A Anderson7 and Gerry F Killeen12345

Author Affiliations

1 Ifakara Health Institute, Coordination Office, PO Box 78373, Kiko Avenue, Mikocheni, Dar es Salaam, United Republic of Tanzania

2 Dar es Salaam City Council, Ministry of Regional Administration and Local Government, United Republic of Tanzania

3 Durham University, School of Biological and Biomedical Sciences, South Road, Durham, DH13LE, UK

4 Liverpool School of Tropical Medicine, Pembroke place, Liverpool, L3QA, UK

5 Swiss Tropical Institute, Department of Public Health and Epidemiology, PO Box 4002, Basel, Switzerland

6 Danish Bilharziaisis Laboratory, 1-D Jaegersborg Allé, Charlottenlund, DK 2920, Denmark

7 Biology Department, University of Winnipeg, Winnipeg, Manitoba, R3B 2E9, Canada

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Malaria Journal 2009, 8:157  doi:10.1186/1475-2875-8-157

Published: 14 July 2009

Abstract

Background

Mosquito 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.

Methods

Novel 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.

Results

The 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.

Conclusion

The 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.