Vector competence of pre-alpine Culicoides (Diptera: Ceratopogonidae) for bluetongue virus serotypes 1, 4 and 8

Abstract

BackgroundBluetongue disease, caused by bluetongue virus serotype 8 (BTV-8), appeared for the first time in the northern part of Europe in 2006, and subsequently rapidly spread causing severe economic losses to the farming industry. The implicated vectors of BTV in Europe are Culicoides species within the subgenus Avaritia (C. chiopterus, C. dewulfi, C. obsoletus and C. scoticus). Epidemiological data from Switzerland have shown that BTV, whose spread was eliminated at an early stage by vaccination campaigns, had not been circulating among livestock at higher altitudes where other species dominate the Culicoides fauna. In this study, we investigated the extent that Culicoides spp. prevailing at higher altitudes (mainly C. grisescens) can act as vectors for BTV.MethodsCulicoides were collected at farms in the pre-alpine region (two sites at 1550 m above sea level, masl, referred to as pre-alpine I; one site at 2030 masl, pre-alpine II) and, for comparative purposes, from the Swiss Plateau (one site, 650 masl). They were fed on bovine blood/BTV suspensions (BTV-1, 4 or 8) and incubated for eight days under a fluctuating temperature regime (13–25 °C, mean 19 °C), reflecting a mid-summer warm spell in the pre-alpine region. Susceptibility to BTV transmission was assessed from head homogenates by RT-qPCR and virus isolation.ResultsOverall, 9196 female Culicoides were exposed to the three BTV strains through an artificial membrane, with feeding rates of 14–27%. Survival rates of blood-engorged Culicoides females at eight days post-infection depended on both virus serotype and altitude of origin. Virus dissemination (Cq ≤ the cut-off value as determined by serial virus dilutions) was confirmed only for BTV-1 in C. scoticus (dissemination efficiency 22.5%; 9/40) and C. obsoletus (5.6%; 1/18) from the Swiss Plateau area. There was no strong evidence of susceptibility to infection for Culicoides from the pre-alpine area when fed with all BTV strains (BTV-1, 4 and 8).ConclusionsThis study confirms the susceptibility of C. scoticus and C. obsoletus to BTV-1 infection, including under cooler temperatures. Culicoides grisescens, which is highly abundant at higher altitudes, cannot be considered a potential vector under these temperature conditions.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3050-y) contains supplementary material, which is available to authorized users.

Update of the Culicoides (Diptera: Ceratopogonidae) species checklist from Algeria with 10 new records

“…Moreover, C. obsoletus and C. scoticus from the UK have been experimentally infected with BTV-8 and BTV-9; C. scoticus exhibiting higher viral titers [86]. Dissemination efficiency has been estimated to be about 20% for BTV-1 in C. scoticus populations in Switzerland [32].…”

“…After collections in different regions of Algeria carried out in the early 1980s, Szadziewski [28] reported 30 species, including 19 new records for the Algerian fauna, increasing the number of known species in Algeria to 40. This inventory encompassed several species known as confirmed or probable BTV vectors, such as C. imicola Kieffer, C. obsoletus Meigen, C. scoticus Downes & Kettle within the subgenus Avaritia and C. newsteadi Austen, C. pulicaris (Linnaeus) and C. punctatus (Meigen) within the subgenus Culicoides [29][30][31][32][33].…”

Development of a Digital RT-PCR Method for Absolute Quantification of Bluetongue Virus in Field Samples

“…Seasonal incursions of the disease in parts of Europe (Mediterranean basin) during the summer cause economic losses due to direct impact on livestock and trade restriction. In the last few years, new serotypes have been identified, probably, originated under evolutionary dynamics and selection pressure (37); new potential vectors have been identified (38,39); some field strains/serotypes proved to be able to transmit vertically or horizontally, to reassort their RNA, and to alter their pathogenicity, specificity, and spread capacity (37). Nowadays, the molecular diagnosis of BTV (real time RT-PCR NS3 ) by Hofmann allows to identify all circulating serotypes.…”

Real-time PCR on skin biopsies for super-spreaders’ detection in bovine besnoitiosis.

“…As noted by Bigalke [7], if mechanical B. besnoiti transmission by Stomoxys calcitrans is of signi cance in the epidemiology of cattle besnoitiosis, the lack of parasite persistence on the mouthparts of stable ies suggests that mechanical transmission may only occur during brief periods of time [30]. This is in contrast with many blood-sucking vectors which are able to transmit pathogens for the rest of their life, such as Culicoides vectors of bluetongue virus [31] or phlebotomine sand y vectors of leishmaniasis [32]. Therefore, in bovine besnoitiosis, the long persistence of infectivity in a minority of subclinical carriers could contribute in a large extent to the spread of the parasite within the herd.…”