Role of different Culicoides vectors (Diptera: Ceratopogonidae) in bluetongue virus transmission and overwintering in Sardinia (Italy)

Abstract

BackgroundBluetongue (BT) epidemics have affected the Mediterranean island of Sardinia since 2000. While Culicoides imicola represents the main bluetongue virus (BTV) vector, other European Culicoides biting midges, possibly implicated in virus transmission, have been detected here. Understanding their distribution, seasonal abundance, and infection rates is necessary to predict disease incidence and spread across coastal and inland areas, and to define their role in virus overwintering.MethodsBiting midge abundance was determined by light traps on selected farms representing diverse climatic conditions of Sardinia. Livestock-associated Culicoides species were morphologically and molecularly identified. Infection rates in prevailing midge species captured in 2013 during a BTV-1 outbreak were determined using RT-qPCR based virus detection in insect body pools, supplemented by specific body region analyses. The seasonal infection prevalence in Culicoides samples collected in 2001 in a BTV-2 affected farm was also determined.ResultsThe Newsteadi complex (C. newsteadi species A and species B) prevailed among all biting midge species (47.7 %), followed by C. imicola (27.8 %) and the Obsoletus complex (C. obsoletus and C. scoticus) (17.6 %). Whilst Culicoides imicola was more abundant along the coast, the Newsteadi complex was frequently collected at higher altitude and the Obsoletus complex was notably associated to cattle farms. Culicoides pulicaris and C. punctatus abundance was found to be marginal in all farms. BTV was detected in parous female samples of all these species, and the full dissemination of the virus within the body of C. imicola, C. obsoletus, C. scoticus, and Newsteadi complex species was confirmed by analyses of thorax and head, containing salivary glands. Higher infection rates were associated with C. scoticus, C. newsteadi species A and species B, compared to C. imicola. The virus was detected in C. newsteadi species A and C. obsoletus in winter and spring, whereas it was mainly found in summer and autumn in C. imicola.ConclusionsIn Sardinia, bluetongue virus is transmitted by multiple Culicoides vectors, including C. imicola and the Newsteadi complex being the most important. The Newsteadi complex and other midge species can play an important role in internal areas and are likely to be directly involved in virus overwintering.

A first estimation of Culicoides imicola and Culicoides obsoletus/Culicoides scoticus seasonality and abundance in Europe

“…Italy (De Liberato et al 2010, Goffredo et al 2013, Foxi et al 2016 Between 17 The present document has been produced and adopted by the bodies identified above as authors. This task has been carried out exclusively by the authors in the context of a contract between the European Food Safety Authority and the authors, awarded following a tender procedure.…”

Schmallenberg virus in Culicoides Latreille (Diptera: Ceratopogonidae) populations in France during 2011-2012 outbreak

“…Although a large species diversity was tested, only nine species were found positive for SBV genome ( C. obsoletus , C. scoticus , C. dewulfi , C. chiopterus , C. pulicaris , C. newsteadi , C. lupicaris , C. imicola and C. nubeculosus ). Most of these species (except for C. nubeculosus and C. lupicaris ) are recorded or suspected to be implicated in BTV transmission in Europe (Carpenter, Lunt, Arav, Venter, & Mellor, ; Foxi et al., ; Goffredo et al., , ; Venail et al., ). Although Veronesi et al.…”

Mechanistic model for predicting the seasonal abundance of Culicoides biting midges and the impacts of insecticide control

“…Overwintering (diapause) behaviour of Culicoides species is generally poorly understood, and depends on location and climate. In locations with mild winters, such as Mediterranean areas, populations may experience continuous development [34], but for locations which experience cold winters, such as northern European areas which we consider here, development is arrested. Field observations indicate that fourth-instar larvae are commonly present over winter [35, 36], and it is largely thought that temperature and/or photoperiod play an important role in determining when adult midges emerge from diapause from their immature stages in their semi-aquatic habitat [37–39].…”