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Open Access Research

Distribution of the species of the Anopheles gambiae complex and first evidence of Anopheles merus as a malaria vector in Madagascar

Jean-Michel Léong Pock Tsy1, Jean-Bernard Duchemin12, Laurence Marrama3, Patrick Rabarison4, Gilbert Le Goff15, Voahirana Rajaonarivelo15 and Vincent Robert15*

Author Affiliations

1 Groupe de Recherche sur le Paludisme, Laboratoire d'Entomologie Médicale, Institut Pasteur de Madagascar, B.P. 1274, Antananarivo 101, Madagascar

2 CERMES, B.P. 10887, Niamey, Niger

3 Unité d'Epidémiologie, Institut Pasteur de Dakar, B.P. 220 Dakar, Sénégal

4 Unité d'Entomologie Médicale, Institut Pasteur de Guyane, B.P. 6010, 97306 Cayenne, France

5 Institut de Recherche pour le Développement, B.P. 434, Antananarivo 101, Madagascar

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Malaria Journal 2003, 2:33  doi:10.1186/1475-2875-2-33

Published: 8 October 2003

Abstract

Background

Members 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.

Methods

Sampling 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.

Results

Three 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.

Conclusion

Despite 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.