Abstract
BackgroundBiting midges belonging to Culicoides imicola, Culicoides obsoletus complex and Culicoides pulicaris complex (Diptera: Ceratopogonidae) are increasingly implicated as vectors of bluetongue virus in Palaearctic regions. Culicoides obsoletus complex includes C. obsoletus (sensu stricto), C. scoticus, C. dewulfi and C. chiopterus. Culicoides pulicaris and C. lupicaris belong to the Culicoides pulicaris complex. The aim of this study was a geo-statistical analysis of the abundance and spatial distribution of Culicoides spp. involved in bluetongue virus transmission. As part of the national bluetongue surveillance plan 7081 catches were collected in 897 Sicilian farms from 2000 to 2013.MethodsOnderstepoort-type blacklight traps were used for sample collection and each catch was analysed for the presence of Culicoides spp. and for the presence and abundance of Culicoides vector species (C. imicola, C. pulicaris / C. obsoletus complexes). A geo-statistical analysis was carried out monthly via the interpolation of measured values based on the Inverse Distance Weighted method, using a GIS tool. Raster maps were reclassified into seven classes according to the presence and abundance of Culicoides, in order to obtain suitable maps for Map Algebra operations.ResultsSicilian provinces showing a very high abundance of Culicoides vector species were Messina (80% of the whole area), Palermo (20%) and Catania (12%). A total of 5654 farms fell within the very high risk area for bluetongue (21% of the 26,676 farms active in Sicily); of these, 3483 farms were in Messina, 1567 in Palermo and 604 in Catania. Culicoides imicola was prevalent in Palermo, C. pulicaris in Messina and C. obsoletus complex was very abundant over the whole island with the highest abundance value in Messina.ConclusionsOur study reports the results of a geo-statistical analysis concerning the abundance and spatial distribution of Culicoides spp. in Sicily throughout the fourteen year study. It provides useful decision support in the field of epidemiology, allowing the identification of areas to be monitored as bases for improved surveillance plans. Moreover, this knowledge can become a tool for the evaluation of virus transmission risks, especially if related to vector competence.
Highlights
Biting midges belonging to Culicoides imicola, Culicoides obsoletus complex and Culicoides pulicaris complex (Diptera: Ceratopogonidae) are increasingly implicated as vectors of bluetongue virus in Palaearctic regions
Culicoides pulicaris complex was mainly found in Messina province and in the eastern area of Palermo province, whilst it was scarcely present in some areas of Trapani, Palermo and Ragusa provinces (Fig. 4)
Culicoides obsoletus complex was especially abundant within the territory of Messina province, while it was less abundant in some areas of Trapani, Catania and Ragusa provinces (Fig. 5)
Summary
Biting midges belonging to Culicoides imicola, Culicoides obsoletus complex and Culicoides pulicaris complex (Diptera: Ceratopogonidae) are increasingly implicated as vectors of bluetongue virus in Palaearctic regions. Breeding sites for Culicoides include a wide range of habitats often located nearby their hosts, in and around farm holdings, such as decaying vegetation, dung, pond borders and moist soils. Their larvae can survive within aquatic sites characterized by different ranges of acidity and salinity [2]. Different species included in the genus Culicoides are of veterinary importance as vectors of different arboviruses causing severe animal diseases. Bluetongue virus (BTV) and African horse sickness virus (AHSV), listed as causative agents of globally important diseases by the OIE (Office International des Epizooties), are transmitted by Culicoides species [3]. Culicoides spp. can transmit filarial diseases such as onchocercosis and mansonellosis, affecting various species including humans [3, 5]
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