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. 2016 Aug 9;9(1):440.
doi: 10.1186/s13071-016-1733-9.

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

Cipriano Foxi  1 , Gavino Delrio  1 , Giovanni Falchi  1 , Maria Giovanna Marche  1 , Giuseppe Satta  2 , Luca Ruiu  3
Affiliations

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

Cipriano Foxi et al. Parasit Vectors. .

Abstract

Background: Bluetongue (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.

Methods: Biting 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.

Results: The 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.

Conclusions: In 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.

Keywords: BTV; Biting midges; Bluetongue; Culicoides vectors; Infection rate; Seasonal abundance; Virus detection; Virus overwintering.

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Figures

Fig. 1
Fig. 1
Map of Sardinia showing the location of study farms and the frequency of livestock-associated Culicoides species
Fig. 2
Fig. 2
Seasonal abundance pattern of Culicoides midges in representative farms selected on the basis of the highest catches of each species and comparing a Northern and a Southern location. Dashed lines represent the nightly number of light-trapped females; solid lines depict the nightly number of parous females
Fig. 3
Fig. 3
Culicoides abundance and BTV prevalence in Sassari-1 during 2001. a) seasonal patterns of abundance of parous females and b) BTV-2 infection prevalence per month
See this image and copyright information in PMC

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