Effects Of Bednet Use, Topography And Targeted Vector Control On Malaria Transmission In The Highlands Of Vihiga And Kakamega Counties, Western Kenya

ABSTRACT

Insecticide-treated bed nets (ITNs) are known to be highly effective in reducing

malaria morbidity and mortality. However, there is scanty information on actual

usage of owned nets which varies among households. Such variations may limit the

potential effect of nets and cause spatial heterogeneity on malaria transmission.

Likewise there is limited information and utilization of topographic parameters such

as the shape of the underlying valley ecosystem in identification of high-risk malaria

foci to help enhance surveillance and targeted vector control activities in regions

where they are most needed. The objective of this study was to determine the effect

of ITNs use, topography and targeted vector control on malaria transmission. The

study was done in; Iguhu, Mbale and Emutete in Vihiga and Kakamega counties, in

malaria hypo-meso-endemic highlands of western Kenya. All houses in study sites

were geo-referenced and mapped. Using a randomized-repeated cross-sectional study

design, residents of 300 households randomly selected from each site in Iguhu and

Emutete were interviewed for ITNs ownership/usage, their houses sprayed for vector

abundance and occupants screened of malaria during the dry and rainy seasons of

2009-2010. Association of topography and spatial distribution of malaria vectors and

infections were determined between broad ‘U’-shaped versus narrow ‘V’-shaped

valley ecosystems in the three sites. Baseline information from spatio-temporal data

above was used to identify intense transmission areas for target vector control using

Indoor Residual Spray (IRS) and Biological larviciding. Entomological and

parasitological data were used for impact evaluation. Data was managed in excel

spread sheets and analyzed by STATA software. Student t-test was done to

determine differences in adult vectors and larval densities while Chi-square test was

done to determine differences in occurrence of malaria infection prevalence.

Univariate and multivariate analysis of Turkey HSD test was done to determine the

most predictive independent variable for the occurrence of larvae, adult vectors and

malaria cases. Despite ITN ownership reaching more than 71%, usage was low at

56.3%. The proportion of non-adherence to ITN use was significantly higher during

the dry season than rainy season, 46.6% vs. 32.9% in Iguhu (χ2= 12.42, d.f. = 1, P