| Description: |
Background Culicoides biting midges exhibit a global spatial distribution and are the main vectors of several viruses of veterinary importance, including bluetongue (BT) and African horse sickness (AHS). Many environmental and anthropological factors contribute to their ability to live in a variety of habitats, which have the potential to change over the years as the climate changes. Therefore, as new habitats emerge, the risk for new introductions of these diseases of interest to occur increases. The aim of this study was to model distributions for two primary vectors for BT and AHS ( Culicoides imicola and Culicoides bolitinos ) using Random Forest (RF) machine learning and explore the relative importance of environmental and anthropological factors in a region of South Africa with frequent AHS and BT outbreaks. Methods Culicoides capture data were collected between 1996 and 2022 across 171 different capture locations in the Western Cape. Predictor variables included climate-related variables (temperature, precipitation, humidity), environment-related variables (NDVI, soil moisture) and farm-related variables (livestock densities). Random Forest (RF) models were developed to explore the spatial distributions of C. imicola, C. bolitinos, and a merged species map, where both competent vectors were combined. The maps were then compared to interpolation maps using the same capture data as well as historical locations of BT and AHS outbreaks. Results Overall, the RF models performed well with 75.02%, 61.6%. and 74.01% variance explained for C. imicola, C. bolitinos and merged species models respectively. Cattle density was the most important predictor variable for both species, whereas sheep density was the second most important for C. imicola, and water vapour pressure was the second for C. bolitinos. In comparison to interpolation maps, the RF models had higher predictive power throughout most of the year when species were modelled individually, however, when merged, the interpolation maps performed ... |