Abstract
The distribution of Bluetongue virus (BTV) in Europe can be represented by two distinct and interconnected epidemiological systems (episystems), each characterized by different ecological characteristics and vector species. This study investigated the vector competence of Italian populations of Culicoides imicola and Culicoides obsoletus/scoticus to some representative BTV strains after artificial oral infection. The BTV strains were selected according to their ability to spread to one or both episystems and included BTV-4 ITA, responsible of the recent Italian and French BTV-4 outbreaks; the BTV-2 strain which caused the first BTV incursion in Italy, Corsica, and Balearic Islands; BTV-4 MOR, responsible for the epidemic in Morocco; and BTV-8, the strain which spread through Europe between 2006 and 2008. Blood-soaked cotton pledgets and Hemotek membrane feeder using Parafilm® membrane were used to artificially feed midges. For each population/strain, recovery rates (positive/tested heads) were evaluated using serogroup- and serotype-specific RT-PCR. The trial demonstrated that, except for the Abruzzo population of C. obsoletus/C. scoticus, which was refractory to BTV-4 MOR infection, all the investigated Culicoides populations are susceptible to the selected BTV strains and that, if prompt vaccination programs and restriction measures had not been implemented, BTV-2 and BTV-4 MOR could have spread all over Europe.
Highlights
Culicoides biting midges (Diptera: Ceratopogonidae) are biological vectors of several important arboviruses such as those causing Bluetongue (BT), African horse sickness, and Epizootic hemorrhagic disease
This study aimed to investigate the vector competence of different Italian populations of Culicoides imicola and C. obsoletus/scoticus to some Bluetongue virus (BTV) strains responsible for recent incursions in the Mediterranean basin and Europe after artificial oral feeding
C. scoticus, which was refractory to BTV-4 MOR infection, all orally infected vector populations tested in this study were able to sustain the BTV strain replication, even that of BTV-4 MOR, a strain which has never been reported in Italy
Summary
Culicoides biting midges (Diptera: Ceratopogonidae) are biological vectors of several important arboviruses such as those causing Bluetongue (BT), African horse sickness, and Epizootic hemorrhagic disease. Because of the direct effect of the disease on animals, but especially because of the ensuing ban on international trade of ruminants and their products between BTV-infected and non-infected areas, outbreaks of Bluetongue virus (BTV) continue to have significant economic impacts in Europe and worldwide. In relation to the spread of BTV strains, two distinct and interconnected epidemiological systems (episystems), with different ecological characteristics and vector species, have been identified in Europe. For BT, it is known that distinct strains of BTV (virus topotypes) vectored by different species of Culicoides occur in specific regions of the world. The topotypes of BTV and the vector species that occur within each episystem are relatively stable, despite extensive and ongoing trade and movement of ruminants between individual episystems
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