Development of a conceptual framework for integrated vector management (IVM) in the heterogeneous malaria ecosystem of western Kenya highlands

Abstract

Malaria heterogeneity in the highlands is due to 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 (LLINs) is the basis of vector control in epidemic prone western Kenya highlands. LLINs 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 (IVM) 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 (IRS) into the existing LLIN programme. Data on malaria vector abundance and parasite prevalence for different malaria ecosystems within western Kenya highlands published before and after mass bed-net distribution campaigns was gathered to assess the efficacy of the LLINs based control efforts. Field tests were carried out to determine the impact of IRS/LLINs combination on vector resting densities in zones where limited or no 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 IRS in IVM 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 of IRS and provides a rationale for judicious integration of IRS within existing ITN based control programmes.