Malaria vector population dynamics in highland and lowland regions of western Kenya

Malaria is the major cause of morbidity and mortality in sub-Saharan Africa. A child below five years dies after every 30 min. Highland areas under land use change impact on malaria transmission by altering the microclimate of the immature stages and adult mosquitoes. Adult vector population dynamics is important because it is an indicator of transmission risk of the disease. This study was to investigate the effects of microclimatic changes on the mosquito indoor-resting behavior.

The study was conducted at a highland site of Marani and at a lowland site of Kombewa where 30 houses were randomly selected at either site. Outdoor and indoor weather conditions were monitored throughout the study period. Indoor mosquitoes were collected using the pyrethrum spray catch method, gonotrophic stage of the females determined and species identified to species level using rDNA polymerase chain reaction method. ELISA was carried out to determine the Plasmodium sporozoites in mosquitoes.

Anopheles gambiae s.s. was more abundant at the highland site whereas An. funestus at the lowland site. Indoor densities were highest in June 2003 at both the sites: An. gambiae at the highland site and An. funestus at the lowland site. There was an association between An. gambiae s.s. abundance and relative humidity at the highland site. Combined entomological inoculation rate (EIR) for both the vector species was 0.4 infected bite per year (ib/yr) at the highland site and 31.1 ib/yr at the lowland site. Prolonged indoor spraying with insecticide decreased vector indoor abundance.