Species Composition And Infection Rates Of Mosquitoes And Sand Flies In Mrima Hill, Kwale County, Kenya

ABSTRACT

Mrima hill in Kwale County, along the Kenyan coast, is known to have high natural background radiation caused mainly by 232 Thorium (Th). Currently, the area also has no proper sanitary disposal system and people use bushes as toilets. There are no fresh water bodies. Despite other parts of the coastal regions of Kenya having been studied for human disease vectors including mosquitoes and sandflies, no studies have been carried out in Mrima hill to establish the prevalence of these important vectors. The main aim of the present study was to determine mosquitoes and sand flies species diversity as well as vector infection rates in order to establish the level of risk of infection with malaria and leishmaniasis for the local inhabitants. The relationship between radiation and population sizes of both mosquitoes and sand flies was determined. This study also established the relationship between levels of radiation and elevation. Thirty eight houses were randomly selected and radiation levels taken using hand held Digilert 100 CPMS reader and recorded. Mosquitoes and sand flies were caught using light traps and counted to establish their population. Species identification was done on mosquitoes and sand flies using standard taxonomic keys. All captured female insects were dissected and examined for presence of parasites to establish the infection rates. Data were analyzed using the Statistical Package for Social sciences (SPSS) Version 20 (2011) utilizing Chi-square and Pearson correlation. A total of 131 mosquitoes and 39 sand flies were captured. Apart from the Aedes aegypti species (1.9%), the only other species of medical importance that were collected in the study area included: Culex pipiens (69.42%), Cx vansomernae (1.5%), Mansonia africana (18.32%) and M. uniformis (9.6%). None of these mosquitoes are known vectors of disease in Kenya. Phlebotomine sand fly species that were collected included Sergentomyia bedfordi (74.36%), S. suberecta (15.35%), S. meilloni (5.12%) S. schwetzi (2.56%) and S. inermis (2.56%). None of these species has been indicated to be of any medical importance in Kenya. The highest radiation level recorded was 17.5 milliSieverts/year whereas the lowest was 5.9 mSv/year; with a mean radiation of 10.52 mSv/year. There was no significant relationship between radiation levels and number of mosquitoes (2 = 103.7; df = 99; P = 0.353) or sandflies (2 = 40.0; df = 55; P = 0.936) collected. There was no significant relationship between the number of mosquitoes and sand flies (2 =36 and P=0.165). In addition, there was no correlation between radiation levels and elevation (r = -0.389; df= 10; P=0.211). From the results of this study it can be concluded that it is unlikely that the insect- borne diseases can occur in Mrima hill, unless the disease causing pathogens are introduced. There is need for further studies to establish the effect of radiation on reproductive capacity and survival of disease vectors in the present study area.