Anopheles gambiae and Anopheles arabiensis population densities and infectivity in Kopere village, Western Kenya

Andrew Ambogo Obala,Barasa O Khwa-Otsyula,Henry D.N Nyamogoba,Helen L Kutima,John H Ouma,Chrispinus J Simiyu,Anne W Mwangi,Gideon N Magak

doi:10.3855/jidc.1979

Abstract

This study was conducted in a sugar belt region of western Kenya interfacing epidemic and endemic malaria transmission. We investigated Anopheles gambiae sensu stricto (ss) and Anopheles arabiensis species compositions and densities, human host choice, and infectivity. Mosquitoes were captured using pyrethrum spray catch technique and first identified based on morphology; species were confirmed by PCR. Blood meal preference and sporozoite rates were determined by ELISA. Parity rates and entomological inoculation rates (EIR) were determined. Seasonal densities were compared against environmental temperatures, relative humidity and rainfall. In total 2,426 An. gambiae were collected. Out of 1,687 female blood-fed mosquitoes, 272 were randomly selected for entomological tests. An. gambiae ss and An. arabiensis comprised 75% (205/272) and 25% (68/272) of the selection, respectively. An. gambiae ss had higher preference for human blood (97%; n=263/272) compared with An. arabiensis, which mostly fed on bovines (88%; n=239/272). The sporozoite and parity rates were 6% (16/272) and 66% (179/272) for An. gambiae ss and 2% (4/272) and 53% (144/272) for An. arabiensis respectively, while EIR was 0.78 infective bites/person/night. Climate (ANOVA; F=14.2; DF=23) and temperature alone (r=0.626; t=3.75; p=0.001) were significantly correlated with vector densities. An. gambiae ss are the most efficient malaria vector mosquito species in Kopere village. Because An. gambiae ss largely rests and feeds indoors, use of indoor residual spray and insecticide-treated nets is likely the most suitable approach to malaria vector control in Kopere village and other parts of Kenya where this species is abundant.

Highlights

This study was conducted in a sugar belt region of western Kenya interfacing epidemic and endemic malaria transmission
The majority of vectors captured indoors in Kopere village, located at an elevation ranging between 1,260 metres and 1,440 metres above sea level, were An. gambiae ss; only a small proportion consisted of An. arabiensis
Githeko et al [12] documented an increased presence of An. arabiensis below the Nandi foothills, where it is the dominant member of An. gambiae found at low altitude in the expansive Kano Plain, especially in the Ahero rice fields where it was shown to be a poor malaria vector

Summary

Introduction

This study was conducted in a sugar belt region of western Kenya interfacing epidemic and endemic malaria transmission. The sporozoite and parity rates were 6% (16/272) and 66% (179/272) for An. gambiae ss and 2% (4/272) and 53% (144/272) for An. arabiensis respectively, while EIR was 0.78 infective bites/person/night. Conclusion: An. gambiae ss are the most efficient malaria vector mosquito species in Kopere village. Because An. gambiae ss largely rests and feeds indoors, use of indoor residual spray and insecticide-treated nets is likely the most suitable approach to malaria vector control in Kopere village and other parts of Kenya where this species is abundant. Reduction of the malaria burden in endemic and epidemic regions requires knowledge of the malariatransmitting mosquito species, populations and behavioural characteristics, and malaria exposure risks. Parity and sporozoite rates, human blood meal preference, and entomological inoculation rates (EIR) are critical indicators of malaria transmission, but they differ

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Conclusion