Abstract
The genus Culicoides Latreille 1809 is a well-known vector for protozoa, filarial worms and, above all, numerous viruses. The Bluetongue virus (BTV) and the recently emerged Schmallenberg virus (SBV) are responsible for important infectious, non-contagious, insect-borne viral diseases found in domestic ruminants and transmitted by Culicoides spp. Both of these diseases have been detected in wild ruminants, but their role as reservoirs during the vector-free season still remains relatively unknown. In fact, we tend to ignore the possibility of wild ruminants acting as a source of disease (BTV, SBV) and permitting its reintroduction to domestic ruminants during the following vector season. In this context, a knowledge of the composition of the Culicoides species communities that inhabit areas where there are wild ruminants is of major importance as the presence of a vector species is a prerequisite for disease transmission. In this study, samplings were conducted in areas inhabited by different wild ruminant species; samples were taken in both 2009 and 2010, on a monthly basis, during the peak season for midge activity (in summer and autumn). A total of 102,693 specimens of 40 different species of the genus Culicoides were trapped; these included major BTV and SBV vector species. The most abundant vector species were C. imicola and species of the Obsoletus group, which represented 15% and 11% of total numbers of specimens, respectively. At the local scale, the presence of major BTV and SBV vector species in areas with wild ruminants coincided with that of the nearest sentinel farms included in the Spanish Bluetongue Entomological Surveillance Programme, although their relative abundance varied. The data suggest that such species do not exhibit strong host specificity towards either domestic or wild ruminants and that they could consequently play a prominent role as bridge vectors for different pathogens between both types of ruminants. This finding would support the hypothesis that wild ruminants could act as reservoirs for such pathogens, and subsequently be involved in the reintroduction of disease to livestock on neighbouring farms.
Highlights
Around 1,400 species of biting midges of the genus Culicoides have been described in the world [1]; some of these are well known transmitters of protozoa, filarial worms and viruses that affect humans and domestic and/or wild animals [2]
Eight species of Culicoides have been described as vectors for Schmallenberg virus (SBV) in Europe: C. obsoletus, C. scoticus, C. dewulfi, C. chiopterus [12, 13, 14], C. punctatus [15], C. pulicaris, C. nubeculosus and C. imicola [16]; all of these are considered vectors of Bluetongue virus (BTV) except C. punctatus and C. nubeculosus
Few studies have been performed on Culicoides populations associated to natural areas with wild ruminants, and most of them are focused on parasites affecting wild bird populations [48,49,50,51,52]
Summary
Around 1,400 species of biting midges of the genus Culicoides have been described in the world [1]; some of these are well known transmitters of protozoa, filarial worms and viruses that affect humans and domestic and/or wild animals [2]. BT has re-emerged in the Mediterranean countries The spread of this disease was initially associated with the introduction and establishment of the main vector for BTV outbreaks in Africa and Southern Europe, the Afro-Asiatic species Culicoides imicola Kieffer, 1913. The virus produces a disease that affects ruminants and which was first detected in Germany and the Netherlands in the summer and autumn of 2011 [17] Since it has spread throughout almost the whole of Europe and its presence was confirmed in Spain (in March 2012) when it affected sheep and goats in the south of the country [18]. Eight species of Culicoides have been described as vectors for SBV in Europe: C. obsoletus, C. scoticus, C. dewulfi, C. chiopterus [12, 13, 14], C. punctatus [15], C. pulicaris, C. nubeculosus and C. imicola [16]; all of these are considered vectors of BTV except C. punctatus and C. nubeculosus
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