Abstract
BackgroundMembers of the Anopheles gambiae complex are amongst the best malaria vectors in the world, but their vectorial capacities vary between species and populations. A large-scale sampling of An. gambiae sensu lato was carried out in various bioclimatic domains of Madagascar. Local abundance of an unexpected member of this complex raised questions regarding its role in malaria transmission.MethodsSampling took place at 38 sites and 2,067 females were collected. Species assessment was performed using a PCR targeting a sequence in the IGS of the rDNA. Analysis focused on the relative prevalence of the species per site, bioclimatic domain and altitude. Infectivity of Anopheles merus was assessed using an ELISA to detect the presence of malarial circumsporozoite protein in the head-thorax.ResultsThree species were identified: An. gambiae, Anopheles arabiensis and An. merus. The distribution of each species is mainly a function of bioclimatic domains and, to a lesser extent, altitude. An. arabiensis is present in all bioclimatic domains with highest prevalence in sub-humid, dry and sub-arid domains. An. gambiae has its highest prevalence in the humid domain, is in the minority in dry areas, rare in sub-humid and absent in sub-arid domains. An. merus is restricted to the coastal fringe in the south and west; it was in the majority in one southern village. The majority of sites were sympatric for at least two of the species (21/38) and two sites harboured all three species.The role of An. merus as malaria vector was confirmed in the case of two human-biting females, which were ELISA-positive for Plasmodium falciparum.ConclusionDespite the huge environmental (mainly man-made) changes in Madagascar, the distribution of An. gambiae and An. arabiensis appears unchanged for the past 35 years. The distribution of An. merus is wider than was previously known, and its effectiveness as a malaria vector has been shown for the first time; this species is now on the list of Malagasy malaria vectors.
Highlights
Members of the Anopheles gambiae complex are amongst the best malaria vectors in the world, but their vectorial capacities vary between species and populations
The Anopheles gambiae complex plays a central role in malaria transmission
Mosquitoes (Tables 1 and additional file 1) were collected at 38 sites distributed within 4 bioclimatic domains (Figure 1 and additional file 1)
Summary
Members of the Anopheles gambiae complex are amongst the best malaria vectors in the world, but their vectorial capacities vary between species and populations. Local abundance of an unexpected member of this complex raised questions regarding its role in malaria transmission. The Anopheles gambiae complex plays a central role in malaria transmission. Grjebine [4] studied the relative abundance of An. gambiae sensu lato as compared to other anopheline species, without making any distinction between the "freshwater species A and B". He demonstrated a continuous distribution at altitude < 1400 m. No saltwater species was identified but Anopheles merus was raised from larvae found in crab-holes in the Betsiboka estuary (near Mahajanga) with 0.7 g NaCl / l
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