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Open Access Research

Larval habitats of Anopheles gambiae s.s. (Diptera: Culicidae) influences vector competence to Plasmodium falciparum parasites

Bernard A Okech126*, Louis C Gouagna23, Guiyun Yan5, John I Githure2 and John C Beier4

Author Affiliations

1 Centre for Biotechnology, Research and Development (CBRD), Kenya Medical Research Institute, P. O. Box 54840, Nairobi, Kenya

2 Human Health Division, International Centre of Insect Physiology and Ecology (ICIPE), P. O. Box 30772, Nairobi, Kenya

3 Département Société et Santé – UR 016, Institut de Recherche Pour le Développement (IRD), P.O. Box 64501, 34394 Montpellier Cedex 5, France

4 Department of Epidemiology and Public Health, University of Miami School of Medicine, 12500 SW, 152nd Street, Building B Miami, FL 33177, USA

5 Program in Public Health, College of Health Sciences, University of California, Irvine, Hewitt Hall, Room 3038, Irvine, CA 92697-4050, USA

6 Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St Augustine, 32080-8610, FL, USA

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Malaria Journal 2007, 6:50  doi:10.1186/1475-2875-6-50

Published: 30 April 2007

Abstract

Background

The origin of highly competent malaria vectors has been linked to productive larval habitats in the field, but there isn't solid quantitative or qualitative data to support it. To test this, the effect of larval habitat soil substrates on larval development time, pupation rates and vector competence of Anopheles gambiae to Plasmodium falciparum were examined.

Methods

Soils were collected from active larval habitats with sandy and clay substrates from field sites and their total organic matter estimated. An. gambiae larvae were reared on these soil substrates and the larval development time and pupation rates monitored. The emerging adult mosquitoes were then artificially fed blood with infectious P. falciparum gametocytes from human volunteers and their midguts examined for oocyst infection after seven days. The wing sizes of the mosquitoes were also measured. The effect of autoclaving the soil substrates was also evaluated.

Results

The total organic matter was significantly different between clay and sandy soils after autoclaving (P = 0.022). A generalized liner model (GLM) analysis identified habitat type (clay soil, sandy soil, or lake water) and autoclaving (that reduces presence of microbes) as significant factors affecting larval development time and oocyst infection intensities in adults. Autoclaving the soils resulted in the production of significantly smaller sized mosquitoes (P = 0.008). Autoclaving clay soils resulted in a significant reduction in Plasmodium falciparum oocyst intensities (P = 0.041) in clay soils (unautoclaved clay soils (4.28 ± 0.18 oocysts/midgut; autoclaved clay soils = 1.17 ± 0.55 oocysts/midgut) although no difference (P = 0.480) in infection rates was observed between clay soils (10.4%), sandy soils (5.3%) or lake water (7.9%).

Conclusion

This study suggests an important nutritional role for organic matter and microbial fauna on mosquito fitness and vector competence. It shows that the quality of natural aquatic habitats of mosquito larvae may influence malaria parasite transmission potential by An. gambiae. This information can be important in targeting larval habitats for malaria control.