First BT epidemic in Sardinia during the year 2000: retrospective georeferentiation of the outbreaks and evaluation of the impact of some climatic and environmental factors in ASL of Sassari

FIRST BT EPIDEMIC IN SARDINIA DURING THE YEAR 2000: RETROSPECTIVE GEOREFERENTIATION OF THE OUTBREAKS AND EVALUATION OF THE IMPACT OF SOME CLIMATIC AND ENVIROMENTAL FACTORS IN ASL OF SASSARI In the year 2000 there was the first occurence of Bluetongue in Sardinia. The first oubreak in Azienda Sanitaria Locale (ASL), district of Sassari, occured in the first decade of september. At the third decade of december the number of outbreaks was about 1000. At that time location of oubreaks has been performed only at the level of single municipality, without individual georeferentiation. Moreover these data were not digital recorded. The absence of georeferantiation did not allowed a punctual correlation between location of the infected flocks and climatic and enviromental data sharing identical coordinates and times. The aim of this preliminar study was to rebuild outbreacks georeferentiation of the first BT epidemic (the only epidemic without any influence of previous immunity on ruminants population) and evaluate the possible correlations with geographic factors (altitude, water bodies, rivers, ecc.), climatic data (temperature) and temporal evolution and spread of outbreaks. We reviewed more than 3000 record cards of the oubreaks of BT in ASL, data from National Database (BDN 2014 census), maps and layers related to the district of Sassari (amministrative borders, satellite imagery, topographic maps, water bodies and rivers, ecc.) climatic data of the year 2000 from 19 weather stations provided by ARPAS. Data were recorded and analyzed using Microsoft Access and Excel, maps and layers were implemented using GIS ESRI Arcview 10.3. Coordinates of flocks were recovered a) from corresponding data of BDN, b) detecting the corresponding location on the map of toponyms of Sardinia (about 5000 features) and satellite maps, c) through interviews with veterinarians and farmers. Altitude of any farms represented the average of height contours in a buffer of 200 meters radius. In regard to climatic factors we considered the average value of a decade of average daily temperatures of each flocks at the likely day 0 of infection, i.e. 30 days before the detection of the outbreak. Presence and proximity of water bodies and rivers to outbreaks was detected integrating the correlated layers and the satellite maps. We detected 977 outbreaks in the area, 718 of these likely started in the month of September alone (clinically detected in October). The 73.79% (721 outbreaks) were located beneath 250 m. of height, the 16.06% (157) between 251 and 350 meters, 9.72% (95) between 351 and 500 meters (the environmental lapse rate ERL has an average of 6.49 K/km). Only 4 outbreaks were above this last limit. The timing of the infections had a strong correlation with high temperature. For example the weather station of Sassari (area with an overall of 280 outbreaks) reported 22.11°C – 22.48°C – 21.56°C (at 0 MASL) for the three decade of September 2000 respectively. It was also observed a strict relation between areas with large presence of water bodies and rivers and location of outbreaks. Results of this preliminary study confirm that BTV transmission, as for other arbovirus, is strongly related to suitable environmental conditions. The use of GIS can contribute not only for georeferencing “cold cases” but to better investigate vector-borne diseases.