Diversity and distribution of immature vectors of malaria and rift valley fever in habitats along an altitudinal gradient in Barigo, Kenya

Abstract

Abstract. Dancan K, Ong’amo GO, Ndegwa P. 2018. Diversity and distribution of immature vectors of malaria and rift valley fever in habitats along an altitudinal gradient in Baringo County, Kenya. Bonorowo Wetlands 8: 25-32. Malaria and RVF are two diseases whose onset of epidemics leads to massive losses in human lives. Infected Anopheles mosquitoes transmit Plasmodium parasites that cause malaria, while infected floodwater Aedes species are responsible for the primary transmission of RVF viruses. The high mobility of adult mosquito species has rendered interventions targeting their behavior ineffective. Thus, interventions that target immature stages an advantageous. For effective implementation of immature stage-based control strategies, information on their diversity and distribution in various habitats distributed along altitudinal gradients is important. This study investigated the diversity and distribution of malaria and RVF mosquito vectors at immature stages along an altitudinal gradient in Baringo County, Kenya, during the short rains season. The species identified in the entire study area (800 m to 2300 m above sea level) were Culex quinquefaciatus, Cx. annulioris, Cx. pipiens, Cx. poicilipes, Cx. tigripes, Anopheles pharoensis, An. gambiae s.l, An. coustani, An. funestus, and Aedes taylori. Altitude was divided into three classes; 800 m to 1300 m, 1301 m to 1800 m, and 1801 m to 2300 m. Aedes taylori and Cx. tigripes were only in the 1801 m to 2300 m altitudinal class while An. funestus was only in the 800 m to 1300 m altitudinal class. The altitudinal class between 1801 m to 2300 m had the lowest Shannon-wiener diversity index (H? = 0.9836) of species (9species). Comparison of mosquitoes collected in habitats in different altitudinal classes revealed variations in the respective species

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counts (?₂² = 127.47; p-value < 0.001). The only species whose distribution showed correlation with altitude was An. pharoensis (r = -0.40; t32 = -2.50; p = 0.02). The highest species diversity was recorded in riverbanks, where the water was clear and vegetation was present. Stepwise regression analysis revealed that the suitability of a habitat for vector breeding was mainly dictated by water quality and the presence of vegetation. The results in this study reveal the need for continuous monitoring of vectors in the low land areas and the highland areas to avoid sudden epidemics of malaria and RVF.