Heterogeneity in distribution of An. Gambiae s.I and 2la chromosomal inversion in western Kenya

Abstract

Environmental heterogeneity determines the distribution of disease vectors. Understanding vector distribution is important in evaluating malaria control measures. An assessment of distribution of An. gambiae was undertaken in low- and high-elevation zones of western Kenya based on 2La inversion. An. gambiae s.s. comprised 90.3% in high-elevation zones while An. arabiensis was 76% in low-elevation zone. The 2La inversion which facilitates local adaptation to degree of aridity showed significant variations in distribution of the two alternative arrangements. Frequency of inverted arrangement (2La) was 14.3% in high-elevation and 52% in low-elevation zones. Frequency of standard arrangement (2La+) was 57.1% in high-elevation and 25% low-lying zones. Observations were that vector species are differentially distributed and adapted to environmental heterogeneities in study areas. Heterogeneous vector system complicates malaria control targeting vector as observed elsewhere in Africa. An. gambiae s.s. along altitudinal gradient deviated significantly from Hardy-Weinberg equilibrium suggesting restricted gene flow, which could relate to differences in microclimatic condition