Anopheline mosquito species composition, density, longevity and malaria prevalence around Gilgel-Gibe area, Southwest Ethiopia

Abstract

Background: Ethiopia has recently constructed dams to produce electricity, irrigate farmlands and control flood to reduce poverty and sustain economic growth, this may result in elevated malaria transmission. In this paper, we investigate the effects of a mega hydropower dam on Anopheles mosquito species composition, density, longevity and malaria prevalence. Method: Longitudinal entomological study was conducted from June –December 2013 in two kebeles (four villages) in Tiro Afeta district, jimma zone Southwest Ethiopia. The two kebeles are; Koticha Gibe, which is located near Gilgel Gibe hydroelectric dam and Decha Nadi, located away from the dam. Anopheline mosquitoes were collected using CDC light trap catches and pyrethrum spray catches. In addition retrospective parasitological study was conducted from June-December 2013. Data were analyzed using SPSS version 16.0 statistical package. Descriptive statistics and student t-test were used during analysis and p-value less than 0.05 was considered statically significant. Results: Overall, 1521 Adult anopheline mosquitoes belonging to two species were collected. An. gambiae s.l. was the predominant species accounting for 72.9% followed by An. coustani s,l (27.1%). Over all mean monthly An. gambiae s.l. density collected by LTCs and PSCs was 5.6 per trap/night and 3.51 per house, respectively. Of these 8.5 per trap/night and 5.6 per house/day of them was collected from kebele located near to the dam (Koticha Gibe) by LTCs and PSCs, respectively and the rest 2.71and 1.95 was collected by the same methods from kebele far from the dam (Decha Nadi). There was significant difference in mean monthly An. gambiae s.l. density between the two kebeles (P ˂ 0.05).There was significant (P < 0.05) difference between mean indoor and outdoor An. gambiae s.l. density. However, there was no significant (P > 0.05) difference between mean indoor and outdoor density of An. coustani s.l between the two kebeles. duration of indoor resting after blood feeding decreased from 1.61to 1.28 and1.35 to 1.23 in Koticha Gibe and Decha Nadi kebele, respectively during Post IRS operations and LLITNs distributions .Over all probability of daily survival of An. gambiae s.l. decreased from 0.70 to 0.56 during Post IRS operations and LLITNs distributions. The prevalence of malaria in the study setting was 10.71%. There was no significance difference in malaria prevalence between two kebeles (x2 = 9.386, P = 0.052). Conclusion: A Clear impact of dam on Anopheline mosquito density has been seen. In other word, the dam is more favorable than the area far from it.