Variations in species composition and infection rates in Anopheles gambiae s.l. across eco-vegetational zones in Nigeria and Cameroon.

Significant variations in vector biology within and between countries have been reported in malaria epidemiological studies1. It is now generally agreed that a clear understanding of the detailed epidemiology of the disease is a pre-requisite to effective malaria control in the African sub-region2. Anopheles gambiae complex (Diptera: Culicidae) is one of the most efficient vectors of Plasmodium falciparum in the African sub-region; it is a complex of sibling taxa3. Two of these sibling species, An. gambiae sensu stricto and An. arabiensis are the major vectors4. Relative abundance of the sibling species varies across eco-vegetational zones5–8. Vector competence among sibling species is dependent on the degree of anthropophily, endophily and ability to recover after the dry season5. Consequently, variations occur in infection rates among sibling species9–10. Two of the problems of malaria vector control in Nigeria are the diversity of anopheline vectors and large size of the country. Infection rates varied across ecological zones in Nigeria11 and Cameroon12. This report focuses on species composition and infection rates from investigations conducted to obtain key entomological indices of An. gambiae s.l. in four villages across eco-vegetational zones in Nigeria (Igbo-Ora and Bama) and Cameroon (Fokoué and Mora). Malaria is perennial and endemic at Igbo-Ora, Bama, Mora and Fokoué, with transmission reaching its peak in August; the density and activity of An. gambiae s.l. in these villages follow the rainfall patterns13. Bama (13.68° E, 11.16° N) and Mora (14.68° E, 11.05° N), villages in the Lake Chad Basin are in the Sudan savanna; Igbo-Ora (3.28° E, 7.43° N) in the Savanna woodland ecotone, between the forested south and the Savanna, while Fokoué (10.12° E, 5.35° N) is located in the hilly savanna woodland of central Cameroon. There are two overlapping seasons in the forest and savanna woodland: November–April (dry), May–October (rainy); the Sudan savanna is characterized by three seasons: hot-dry (February– May); rainy (June–September) and dry humid (October–January). Detailed description of Igbo-Ora has been documented elsewhere14.