In the western highlands of Kenya malaria is an unpredictable disease with increasing frequency and intensity of transmission. Sometimes the disease occurs in form of severe outbreaks and epidemics that result in loss of human life and exerts a strain on public health services. This underscores the continued need for better understanding of the determinants of transmission of the disease in order to formulate specific and focused intervention strategies. A one year study was undertaken in two study sites in Nandi district in the western highlands of Kenya to determine diversity and abundance of Anopheles species, and parasite species most associated with the disease. Adult Anopheles mosquitoes were sampled biweekly from randomly selected houses by pyrethrum spray capture method and light traps. Larval mosquitoes were sampled from breeding sites by standard dippers and reared into adult stages under laboratory conditions. Adult Anophelesspecies were identified based on morphological features and sibling species by polymerase chain reaction (PCR). Microscopic examination of blood smears was used to confirm malaria infection, to identify Plasmodium species and determine species prevalence. Anopheles gambiae s.l was the most prevalent known vector contributing 95.4%, with Anopheles funestus and Anopheles arabiensis 2.3% each. All A. gambiae s.l samples were identified as A. gambiae s. s. suggesting that this could be the only sibling species of the A. gambiae complex present in study area. Plasmodium falciparum was the most prevalent (90%) whilePlasmodium malariae was 10%. There was significant difference in the malaria parasite species prevalence (c2 P<0.05) but there was no significant difference in the parasite species prevalence between the study sites (c2 P>0.05). The epidemiological significance of known malaria vectors and non-vector anopheles species is discussed.
Key words: Malaria, prevalence, anopheles, sibling species.
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