Il virus della Bluetongue: influenza delle variabili climatiche e ambientali nella diffusione dell’insetto vettore Culicoides imicola attraverso strumenti di analisi statistica e geostatistica in ambiente R e GIS

Bluetongue virus is a non-contagious infectious disease that affects ruminant animal species. Hematophagous insects, of the genus Culicoides, which are the main vector for spreading the disease, transmit the virus. Among them, Culicoides imicola, native to tropical and subtropical areas, has managed to adapt to temperate climates and spread to Italy as well, contributing to the transmission of the disease. The aim of the paper is to identify the climatic-environmental variables that most influence the presence of the vector through a model applied to produce a risk map of the spread of disease, focused on the Sicily region. The data examined by the National Bluetongue Surveillance Plan refer to 162 entomological surveillance sites, in which the search for the vector Culicoides imicola was carried out in the period 2020-2021. This dataset was accompanied by that of animal movements. The geographical distribution analysis showed that the movements, albeit relatively, contributed to the spread of the insect, in areas where its presence was absent, thus propagating the virus, represented by Bluetongue outbreaks. Open-access climatic, environmental and topographic variables were used in backward stepwise logistic regression analysis through open source software, to identify those that most influence the spread of the insect. The results, considering the dataset referring to the entire national territory, did not show significant influences of climatic-environmental variables on the presence of the virus. Focusing the analysis only on the Sicily region, some variables seem to significantly influence the presence of the Culicoides imicola, negatively with the altitude and the clay content in the soil and positively with the land surface temperature in the night.