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Equivalent susceptibility of Anopheles gambiae M and S molecular forms and Anopheles arabiensis to Plasmodium falciparum infection in Burkina Faso

Awa Gnémé12, Wamdaogo M Guelbéogo1, Michelle M Riehle5, Antoine Sanou1, Alphonse Traoré1, Soumanaba Zongo1, Karin Eiglmeier34, Gustave B Kabré2, N’Falé Sagnon1 and Kenneth D Vernick345*

Author Affiliations

1 Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso

2 Université de Ouagadougou, Ouagadougou, Burkina Faso

3 Department of Parasitology and Mycology, Unit of Genetics and Genomics of Insect Vectors, Institut Pasteur, Paris, France

4 CNRS Unit of Hosts, Vectors and Pathogens (URA3012), Paris, France

5 Department of Microbiology, University of Minnesota, Minneapolis, Minnesota, USA

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Malaria Journal 2013, 12:204  doi:10.1186/1475-2875-12-204

Published: 14 June 2013

Abstract

Background

The Anopheles gambiae sensu lato (s.l.) species complex in Burkina Faso consists of Anopheles arabiensis, and molecular forms M and S of Anopheles gambiae sensu stricto (s.s.). Previous studies comparing the M and S forms for level of infection with Plasmodium falciparum have yielded conflicting results.

Methods

Mosquito larvae were sampled from natural pools, reared to adulthood under controlled conditions, and challenged with natural P. falciparum by experimental feeding with blood from gametocyte carriers. Oocyst infection prevalence and intensity was determined one week after infection. DNA from carcasses was genotyped to identify species and molecular form.

Results

In total, 7,400 adult mosquitoes grown from wild-caught larvae were challenged with gametocytes in 29 experimental infections spanning four transmission seasons. The overall infection prevalence averaged 40.7% for A. gambiae M form, 41.4% for A. gambiae S form, and 40.1% for A. arabiensis. There was no significant difference in infection prevalence or intensity between the three population groups. Notably, infection experiments in which the population groups were challenged in parallel on the same infective blood displayed less infection difference between population groups, while infections with less balanced composition of population groups had lower statistical power and displayed apparent differences that fluctuated more often from the null average.

Conclusion

The study clearly establishes that, at the study site in Burkina Faso, there is no difference in genetic susceptibility to P. falciparum infection between three sympatric population groups of the A. gambiae s.l. complex. Feeding the mosquito groups on the same infective blood meal greatly increases statistical power. Conversely, comparison of the different mosquito groups between, rather than within, infections yields larger apparent difference between mosquito groups, resulting from lower statistical power and greater noise, and could lead to false-positive results. In making infection comparisons between population groups, it is more accurate to compare the different groups after feeding simultaneously upon the same infective blood.

Keywords:
Anopheles gambiae; Anopheles arabiensis; Plasmodium falciparum; Malaria vector; Genetic susceptibility; Molecular form; Infection prevalence; Infection intensity