Browsing by Author "Uusitalo, Ruut"

Mosquitoes are arguably amongst the most economically and socially important animals on the planet due to their ability to act as vectors for pathogens, including parasites and viruses, from animals to humans, or between humans. Mosquito-borne diseases (MBDs), are contracted following infection by one or more mosquito borne viruses (MBVs) or parasites, including dengue virus (DENV), chikungunya virus (CHIKV), Zika virus (ZIKV), West Nile virus (WNV), yellow fever virus (YFV) and malaria, and annually cause more than one million human deaths (WHO 2016). MBDs are contracted after an infected mosquito transfers one or more pathogens in the course of blood feeding from one host to another. Three important genera which act as vectors for many pathogens are Anopheles, Culex and Stegomyia and they are most problematic in the tropical and subtropical regions of Asia, South America and Africa (WHO 2016). Among vector-borne diseases (VBDs), MBDs have the strongest dependence on environmental factors. These factors have either direct or indirect impact on mosquito presence and abundance as mosquitoes are dependent on habitat suitability. This study will utilize species distribution modeling (SDM) to investigate the relationship between environmental, anthropogenic and distance factors on the occurrence of mosquito species. It forms part of an ongoing Wildlife screening project, led by Prof. Olli Vapalahti, which aims to screen mosquitoes, rodents and bats for new and known viruses in Kenya. The absence of previous studies of the geographical distribution and habitat suitability patterns of mosquito species over the Taita Hills region in southeastern Kenya, justifies the need for this research. This project has three main objectives: 1) to investigate which mosquito genera are distributed in the Taita Hills, and how they are distributed, 2) to examine which factors best explain the presence of Culex and Stegomyia mosquitoes, 3) to test whether any of the available statistical regression models can reliably estimate the distribution of Culex and Stegomyia mosquitoes, and to build predictive maps for estimations created by the most reliable models. Biological, Geographic Information Systems (GIS) and statistical methods were combined in the study. Data consists of occurrence, environmental, anthropogenic, distance and biological data. The specimens were collected from 122 locations from January–March 2016 throughout the Taita Hills. Environmental, anthropogenic and distance data were acquired from the satellite and aerial imagery and produced in ArcMap. The biomod2 package, intended for ensemble forecasting of species distributions in R, was used to generate models. After multicollinearity of the environmental, anthropogenic and distance factors was pruned, the best estimating predictor variables were selected. The factors that best estimated the distribution of Culex were slope, human population density, NDVI, distance to roads and elevation. This resulted in six reliable models with accurate estimation values. Multivariate adaptive regression splines (MARS) resulted area under the curve (AUC)- value of 0.806, and a traditional Generalized linear model(GLM) brought an AUC- value of 0.730 with high statistical significance rates, both above the value for a good model fit (AUC ≥ 0.7); thus ensuring a reliable estimation. Five environmental, anthropogenic and distance factors best estimated the distribution of Stegomyia: mean radiation in January–March, human population density, NDVI, distance to roads and mean temperature in January–March. By these predictors, biomod2 resulted in highest AUC- values for generalized boosted model (hereafter GBM) and random forest (RF) with AUC- value of 0.708 for each. Hence, reliable estimations resulted for both Culex and Stegomyia, which are visualized by the probability of presence maps in the Results chapter. The results may be used as a guide for public health officials in the Taita region regarding the distribution, favorable habitats and prevention strategies of Culex and Stegomyia mosquitoes, which are capable of transmitting mosquito-borne infections.