Diversity And Distribution Of Immature Vectors Of Malaria And Rift Valley Fever In Habitats Along An Altitudinal Gradient In Baringo County, Kenya.

Abstract

Malaria and RVF are two diseases whose onset of epidemics leads to massive losses in human lives. Both diseases are transmitted by infected mosquito vectors. Infected Anopheles mosquitoes transmit plasmodium parasites that cause malaria while infected flood water Aedes species is responsible for primary transmission of RVF viruses. Most scientists are biased on adult stage control of mosquito species. However, the high mobility of adults has enabled them to adopt, changing their biting and resting patterns such that interventions targeting their behavior are rendered ineffective. This makes interventions that target immature stages more 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. It was conducted between June and September 2014, which was during the short rains. The species identified in the entire study area (800m to 2300m altitude) 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; 800m to 1300m, 1301m to 1800m and 1801m to 2300m. Aedes taylori and Culex tigripes were only in the 1801m to 2300m altitudinal class while An. funestus was only in the 800m to 1300m altitudinal class. The altitudinal class between 1801m to 2300m, had the lowest Shannon-wiener diversity index (Hʹ=0.9836) and the highest number of species (9species). Comparison of mosquitoes collected in habitats in different altitudinal classes revealed variations in the respective species counts ( 29 =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 river banks where the water was clear and vegetation present. Stepwise regression analysis revealed that 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 not only in the low land areas but also in the highland areas to avoid sudden epidemics of malaria and RVF.