Malaria vector species distribution and seasonal population dynamics across varied ecological zones in Baringo County, Kenya

Vector populations fluctuate on a seasonal basis annually. Knowledge on seasonal abundance and distribution of vector species at the local level would improve vector control programmes and contribute to malaria prevention. Despite this, information on malaria vector species distribution and seasonal fluctuations in Baringo County is scarce. This study examined distribution and seasonal abundance of malaria vector species in Baringo. The study area was stratified into four ecological zones namely; lowland, riverine, midland and highland. Monthly collection of outdoor and indoor mosquitoes was conducted between June 2015 and May 2016 using CDC light traps and pyrethrum spray collection respectively. A total of 6,113 anopheline mosquitoes belonging to four species were collected across the four ecological zones. Anopheles gambiae was the most abundant malaria vector species accounting for (93.8%) while An. pharoensis and An. funestus accounted for 4.8% and 1.1% respectively. Mosquitoes were mainly collected from lowlands (79.8%) and riverine (19.0%) zones. Malaria vector abundance was higher in the dry season compared to the rainy season. Anopheles gambiae abundance showed high positive correlation with rainfall in the riverine zone only (r=0.7). Knowledge gained from this study, on malaria vector species distribution and seasonal abundance at local level, is important in implementation of control strategies against malaria by the Baringo County Health Department. The findings highlight the seasons when malaria cases are likely to be higher due to vector abundance and also inform specific areas to target for intervention.