Mapping exposure of Cattle to Rift valley Fever virus along their Migratory Routes

Abstract

Aedes mosquito is the primary vector for Rift Valley fever virus which affects humans and animals. Virus transmission pathways in animals occurs when bitten by infected mosquito or when viremic animals relocate to new regions with competent mosquitoes. Though Rift Valley fever is a transboundary disease with serious economic consequences, movement of viremic animals in search of pasture or trade in spreading the diseases is not fully understood. This research was undertaken in order to better understand the cattle spatial ecology, especially for pastrolist and their interaction with vectors habitat. Using 11 collared herds between 2012 to 2015, kernel density estimator was used to established their utilization distribution while species distribution modeling was used to map vector distribution. The environmental layers used to map environmental space of the sample vectors included topographic wetness index, soil type, phenological variables from satelitte derived normalized difference vegetatoon index (NDVI) and Africlim bioclimatic envelopes. The animal movement patterns were further used to characterize the herd’s core grazing areas using generalized linear modeling. The animal tracking results showed that all herds had limited movement during rainy seasons while during dry seasons they covered an average of 120km in 10 days in search of pastures.Climatic conditions, vegetation seasonality, vapotranspiration and soil types were key determinants of space use within home ranges (p value < 0.05). Similar environmental layers contributed most in defining suitable vector habitats for mosquito species. A vector distribution map generated with an accuracy of Area Under Curve of 0.76 showed suitable habitat coinciding with core grazing areas. Results indicated that movement patterns of pastarolist and vectors habitats are majorly influenced by climatic conditions and vegetation seasonality. Distance covered in search of pasture has the potential of introducing the disease in new regions. Vector control and vaccination of animals, therefore, require to be focused in core grazing areas to reduce disease spread.