Development of a Conceptual Framework for Integrated Vector Management in the Heterogeneous Malaria Ecosystem of Western Kenya Highlands
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Abstract
Malaria heterogeneity in the highlands is due to range of factors including seasonal weather changes, climate variability, land-use changes, topography, drug resistance, and malaria control programs. High coverage of long lasting insecticide treated nets is the basis of vector control in epidemic prone western Kenya highlands. Long lasting insecticide treated nets have effectively controlled malaria in the hypo-endemic zones, but not in meso-endemic and hyper-endemic zones where significant residue of transmission remains despite control efforts.
Inadequate policy on integrated vector management application for ecologically heterogeneous ecosystems hinders effective malaria control. Advances in ecological and epidemiological studies have improved our understanding on vector distribution determinants and malaria transmission enabling us to effectively integrate indoor residual spraying into the existing long lasting insecticide treated nets programme.
Data on malaria vector abundance and parasite prevalence for different malaria ecosystems within western Kenya highlands before and after mass insecticide treated bed-net distribution campaigns was gathered to assess the efficacy of the long lasting insecticide treated nets based control efforts. Field tests were carried out to determine the impact of combined indoor residual spray and long lasting insecticide treated nets on vector indoor resting densities in zones where insecticide treated nets alone had limited efficacy or zero efficacy was observed.
Female An. gambiae s.l resting densities of 0.1 mosquitoes/ house/night were associated with a plasmodium falciparum (pf) prevalence rate of 10% or below. This observation enabled the development of a framework for the inclusion of indoor residual spray in integrated vector management with the suggestion that IRS should be applied in malaria eco-epidemiological zones where An. gambiae s.l resting densities exceeds 0.1 females/ house/ night.
Similarly, only those houses with a resting density of 0.1 females An. gambiae s.l and above should be targeted during spraying. Such an approach would significantly reduce the cost associated with indoor residual spray and provides a rationale for judicious integration of indoor residual spray within existing long lasting insecticide treated nets control programmes.
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