Abstract

The study investigated the use of targeted indoor residual spraying (IRS) as a single malaria intervention in the western highlands, Kenya. Houses were randomly selected in study sites and IRS targeted 30% of houses at focal sites ‘hotspots’ at valley bottoms. Indoor resting densities of adult Anopheles gambiae s.s were monitored biweekly by pyrethrum spray capture in sprayed and control houses. Microscopic examination of blood smears were used to confirm malaria infection and records on malaria cases from health centers were analyzed and used to determine changes in malaria prevalence.  The indoor A. gambiae s.s declined after IRS. Low vector densities were also recorded in the control houses with no malaria cases.  Malaria cases reported at health centers dramatically declined after the targeted IRS. Low coverage targeted IRS was effective as a single intervention strategy as it led to decline in annual disease prevalence from 12 to 1% in the study sites. The effectiveness of targeted IRS appeared to be dependent on anthropophily of the local vector, its susceptibility to the insecticide and seasonal nature of malaria transmission.

Key words: Malaria prevalence, IRS, malaria vector.