Abstract
BackgroundThe different taxa belonging to Anopheles gambiae complex display phenotypic differences that may impact their contribution to malaria transmission. More specifically, their susceptibility to infection, resulting from a co-evolution between parasite and vector, might be different. The aim of this study was to compare the susceptibility of M and S molecular forms of Anopheles gambiae and Anopheles arabiensis to infection by Plasmodium falciparum.MethodsF3 progenies of Anopheles gambiae s.l. collected in Senegal were infected, using direct membrane feeding, with P. falciparum gametocyte-containing blood sampled on volunteer patients. The presence of oocysts was determined by light microscopy after 7 days, and the presence of sporozoite by ELISA after 14 days. Mosquito species and molecular forms were identified by PCR.ResultsThe oocyst rate was significantly higher in the molecular S form (79.07%) than in the M form (57.81%, Fisher's exact test p < 0.001) and in Anopheles arabiensis (55.38%, Fisher's exact test vs. S group p < 0.001). Mean ± s.e.m. number of oocyst was greater in the An. gambiae S form (1.72 ± 0.26) than in the An. gambiae M form (0.64 ± 0.04, p < 0.0001) and in the An. arabiensis group (0.58 ± 0.04, vs. S group, p < 0.0001). Sporozoite rate was also higher in the molecular form S (83.52%) than in form M (50.98%, Fisher's exact test p < 0.001) and Anopheles arabiensis 50.85%, Fisher's exact test vs. S group p < 0.001).ConclusionInfected in the same experimental conditions, the molecular form S of An. gambiae is more susceptible to infection by P. falciparum than the molecular form M of An. gambiae and An. arabiensis.
Highlights
The different taxa belonging to Anopheles gambiae complex display phenotypic differences that may impact their contribution to malaria transmission
When analysed globally for all the four experiments, infection rate was higher in the An. gambiae S group (79.07%) than in the two other groups (55.38% for An. arabiensis and 57.81% for An. gambiae M respectively, Fisher’s exact test p < 0.001 for each)
On the other hand no significant difference was found between An. arabiensis and An. gambiae M groups (Fisher exact test p = 0.29)
Summary
The different taxa belonging to Anopheles gambiae complex display phenotypic differences that may impact their contribution to malaria transmission. Their susceptibility to infection, resulting from a co-evolution between parasite and vector, might be different. In Africa, species belonging to the Anopheles gambiae complex are responsible for a large proportion of malaria cases. This complex is composed of species morphologically identical but distinct in their distribution, ecology and contribution in malaria transmission. The exophilic behaviour of the taxa explains that it was not sampled before in dwellings This new vector may have major importance in malaria transmission as it was found to be more susceptible to infection that the endophilic vectors. The study did not compare susceptibility of the already known species in the An. gambiae complex
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