Methods to collect Anopheles mosquitoes and evaluate malaria transmission: A comparative study in two villages in Senegal

<p>Abstract</p> <p>Background</p> <p>Various methods have been studied as replacement of human landing catches (HLC) for mosquito sampling in entomological studies on malaria transmission. Conflicting results have been obtained in comparing relative efficiency of alternative methods, according to the area, the species present and their density. The aim of this study was to compare the number and characteristics of mosquitoes sampled in two areas of Senegal by three different methods: HLC, light traps adjacent to an occupied bed net (LT/N), pyrethrum spray catches (PSC).</p> <p>Methods</p> <p>Collections were performed in two villages: Dielmo (Soudan savanna) and Bandafassi (Soudan Guinean savanna), two or three nights per month for a 4-5 months period during the maximal transmission season in 2001-2002. Species were identified and <it>Plasmodium </it>infection determined by ELISA. The specific composition, circumsporozoite protein rate and entomological inoculation rate were calculated.</p> <p>Results</p> <p>The diversity of mosquito species captured was maximal with LT/N, minimal with PSC. The mean number of anopheles captures each night was significantly different according to the method used and the species. PSC displayed a significantly lower anopheles density. HLC was the most efficient sampling method when <it>Anopheles gambiae </it>was the main vector (in Bandafassi); LT/N when it was <it>Anopheles funestus </it>(in Dielmo). A significant correlation was found between HLC and LT/M but correlation parameters were different according to the species. Circumsporozoite protein rates were not significantly different between methods or species. The entomological inoculation rate varied along with vector density and thus with methods and species.</p> <p>Conclusions</p> <p>The choice of sampling method influenced entomological data recorded. Therefore, the sampling technique has to be chosen according to the vector studied and the aim of the study. Only HLC must be considered as the reference method, but in some conditions LT/N can be used as an alternative method.</p

Comparative susceptibility to <it>Plasmodium falciparum </it>of the molecular forms M and S of <it>Anopheles gambiae </it>and <it>Anopheles arabiensis</it>

<p>Abstract</p> <p>Background</p> <p>The different taxa belonging to <it>Anopheles gambiae </it>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 <it>Anopheles gambiae </it>and <it>Anopheles arabiensis </it>to infection by <it>Plasmodium falciparum</it>.</p> <p>Methods</p> <p>F3 progenies of <it>Anopheles gambiae s.l</it>. collected in Senegal were infected, using direct membrane feeding, with <it>P. falciparum </it>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.</p> <p>Results</p> <p>The 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 <it>Anopheles arabiensis </it>(55.38%, Fisher's exact test vs. S group p < 0.001). Mean ± s.e.m. number of oocyst was greater in the <it>An. gambiae </it>S form (1.72 ± 0.26) than in the <it>An. gambiae </it>M form (0.64 ± 0.04, p < 0.0001) and in the <it>An. arabiensis </it>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 <it>Anopheles arabiensis </it>50.85%, Fisher's exact test vs. S group p < 0.001).</p> <p>Conclusion</p> <p>Infected in the same experimental conditions, the molecular form S of <it>An. gambiae </it>is more susceptible to infection by <it>P. falciparum </it>than the molecular form M of <it>An</it>. <it>gambiae </it>and <it>An. arabiensis</it>.</p