Abstract
BackgroundAn initial study of genetic diversity of Plasmodium falciparum in Asembo, western Kenya showed that the parasite maintained overall genetic stability 5 years after insecticide-treated bed net (ITN) introduction in 1997. This study investigates further the genetic diversity of P. falciparum 10 years after initial ITN introduction in the same study area and compares this with two other neighbouring areas, where ITNs were introduced in 1998 (Gem) and 2004 (Karemo).MethodsFrom a cross-sectional survey conducted in 2007, 235 smear-positive blood samples collected from children ≤15-year-old in the original study area and two comparison areas were genotyped employing eight neutral microsatellites. Differences in multiple infections, allele frequency, parasite genetic diversity and parasite population structure between the three areas were assessed. Further, molecular data reported previously (1996 and 2001) were compared to the 2007 results in the original study area Asembo.ResultsOverall proportion of multiple infections (MA) declined with time in the original study area Asembo (from 95.9 %-2001 to 87.7 %-2007). In the neighbouring areas, MA was lower in the site where ITNs were introduced in 1998 (Gem 83.7 %) compared to where they were introduced in 2004 (Karemo 96.7 %) in 2007. Overall mean allele count (MAC ~ 2.65) and overall unbiased heterozygosity (He ~ 0.77) remained unchanged in 1996, 2001 and 2007 in Asembo and was the same level across the two neighbouring areas in 2007. Overall parasite population differentiation remained low over time and in the three areas at FST < 0.04. Both pairwise and multilocus linkage disequilibrium showed limited to no significant association between alleles in Asembo (1996, 2001 and 2007) and between three areas.ConclusionsThis study showed the P. falciparum high genetic diversity and parasite population resilience on samples collected 10 years apart and in different areas in western Kenya. The results highlight the need for long-term molecular monitoring after implementation and use of combined and intensive prevention and intervention measures in the region.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-1003-x) contains supplementary material, which is available to authorized users.
Highlights
An initial study of genetic diversity of Plasmodium falciparum in Asembo, western Kenya showed that the parasite maintained overall genetic stability 5 years after insecticide-treated bed net (ITN) introduction in 1997
Following the initial introduction of ITNs in Asembo in 1997 and Gem in 1998, malaria transmission was reduced by 90 % at the early stages of ITNs trial, with the entomology inoculation rate (EIR) falling from 61.3 infective bites per person per year to 1.3 in 2001 [4, 13]
Since the Asembo 2007 survey comprised children up to 15 years of age, initial data were stratified by age (≤5and >5-year-old) and tested for differences in parasite genetic diversity (Additional file 1: Table S1, Additional file 2: Table S2)
Summary
An initial study of genetic diversity of Plasmodium falciparum in Asembo, western Kenya showed that the parasite maintained overall genetic stability 5 years after insecticide-treated bed net (ITN) introduction in 1997. In western Kenya, the efficacy of ITNs in reducing morbidity and all-cause mortality in children under 5 years of age was demonstrated previously [2,3,4,5]. By 2008, the Demographic Household Survey (DHS) showed overall 61 % Kenyan households owned at least one net of any kind and 47 % of children under 5-year-old slept under ITNs [7]. Changes in malaria transmission due to the use of ITNs impact vector and parasite populations, but the effects, especially after scale-up of ITNs, on genetic diversity and parasite populations are still unclear [10, 11]
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