Species Composition, Seasonal Variation and Roles of Anopheles Mosquitoes in the Transmission of Malaria in Koka villages, Central Ethiopia

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Addis Ababa University


Entomological studies on the species composition, seasonal variation and infection rates of Anopheles mosquitoes were conducted at four selected villages of Koka area, Central Ethiopia, between December 2006 and November 2007. Collection and identification of larvae of Anopheles from various breeding habitats during the study period indicated that there are three species, namely Anopheles gambiae s.l. (84.7%), An. pharoensis (14.4%) and An. squamosus (0.9%). Similarly, a total of 8, 279 adult anophelines mosquitoes representing three species were collected through indoor (7784) and outdoor (495) samplings. Overall, An. gambiae s.l. was the predominant species, making 90.1% of all collections followed by An. pharoensis (9.6%). Both species were abundant after the short rainy season and remained high through the wet season, and declined in the dry season. Peak indoor resting density was observed in May. The ratio of fed to half gravid and gravid combined for An. gambiae s.l. in indoor resting collection was 4.9:1, indicating high degree of exophily in the study area. This was also supported by high number of half-gravid and gravid An. gambiae s.l. in outdoor collection than indoor. Similarly, high exophilic behavior (3.5:1) for An. pharoensis was also observed. Of 662 An. gambiae s.l. and 246 An. pharoensis dissected from all collections; the average parous rate was 31.4% and 28.0%, respectively. None of the 208 parous An. gambiae s.l and 69 parous An. pharoensis analyzed by ELISA to detect sporozoite antigen of P. falciparum and P. vivax were found infected. This seems to support the parasitological data during the study period. Although no sporozoite infection rates was detected An. gambiae s.l. (presumably An. arabiensis) seems the principal vector of malaria in the area.