SPATIO -TEMPORAL DISTRIBUTION AND RISK FACTORS ASSOCIATED WITH PHLEBOTOMINE SAND FLIES AND LEISHMANIASIS IN Mt. ELGON REGION, KENYA

Abstract

This study determined the spatio–temporal distribution, natural infection and risk factors associated with phlebotomine sand flies and leishmaniasis in Mt. Elgon focus in 2015. Collections of sandflies were carried out for five nights of each month at two sites each in Bungoma and Trans Nzoia. Eight CDC light traps were set up at each study site from 6:00 pm to 6:00 am and the sandflies from each catch immediately preserved in ethanol for laboratory analyses. Seasonal fluctuation in sandfly population was compared using densities obtained from the CDC light trap collections. Sandfly abundance determined as quantitiative counts per site. Differences in abundance were analyzed using Kruskall Wallis Test. Sex ratio of sandflies was calculated as: No. of male/No. of female × 100 and differences in sex ratio values determined using chi-square test. Shannon Weiner index was calculated to determine the diversity of the sandflies among sites. The environmental factors were recorded as mean per replicate and the differences per site analyzed using One Way ANOVA and spatial and temporal differences analyzed using Two Way ANOVA. The relationships between environmental factors and abundance of the sandfly were determined using correlation coefficient tests. A total of 657 sandfly specimens belonging to one species of Phlebotomus pedifer were collected from both sites, where higher abundance of the flies occurred in Trans Nzoia than at Bungoma, with higher female to male ratios. Seasonality was an important factor causing differential distrubution of Phlebotomus where highest abundance occurred during the dry season. The natural infection rate with Leishmania was lower (8.9%) in Bungoma compared to Trans Nzoia where the rate was over 18.5%. Abundance of sandfly was negatively correlated with soil temperature, rainfall and relative humidity. The variation of case age-groups and the fact that all the cases were found in peri-urban areas suggests that there is an active transmission going on with Phlebotomus pedifer as the only vector in all the allopatric areas studied. It can also be concluded that, like Phlebotomus papatasi, Phlebotomus pedifer can also cause transmission away from rural areas. Based on the results of the current study, it is recommended that there is need molecular identification of sandfly are required to distinguish between subtypes. The environmental characteristics identified as risk factors should inform implementation of targeted vector control strategies. People should be advised not to enter the caves because they can be infected when they are are unprotected.