No abstract

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Copyright Bluetongue

Bluetongue virus (BTV) is the cause of an economically important arboviral disease of domestic and wild ruminants. The occurrence of BTV infection of livestock is distinctly seasonal in temperate regions of the world, thus we determined the dynamics of BTV infection (using BTV-specific real time reverse transcriptase polymerase chain reaction) among sentinel cattle and vector Culicoides sonorensis (C. sonorensis) midges on a dairy farm in northern California throughout both the seasonal and interseasonal (overwintering) periods of BTV activity from August 2012 until March 2014. The data confirmed widespread infection of both sentinel cattle and vector midges during the August – November period of seasonal BTV transmission, however BTV infection of parous female midges captured in traps set during daylight hours also was detected in February of both 2013 and 2014, during the interseasonal period. The finding of BTV-infected vector midges during mid-winter suggests that BTV may overwinter in northern California by infection of long-lived female C. sonorensis midges that were infected during the prior seasonal period of virus transmission, and reemerged sporadically during the overwintering period; however the data do not definitively preclude other potential mechanisms of BTV overwintering that are also discussed.

Bluetongue is an important viral disease of ruminants that is transmitted by hematophagous Culicoides midges. We examined the seasonal patterns of abundance and infection of Culicoides sonorensis (C. sonorensis) at 4 dairy farms in the northern CentralValley of California to develop estimates of risk for BTV transmission to sentinel cattle at each farm. These 4 farms were selected because of their similar meteorological conditions but varying levels of vector abundance and BTV infection of cattle (Mayo et al., 2011). C. sonorensis midges were collected weekly at each farm during the seasonal transmission period, using three different trapping methods: traps baited with either carbon dioxide (CO 2 ) alone or traps with CO 2 and UV light, and by direct aspiration of midges from sentinel cattle. Analysis of BTV-infected midges using group and serotypespecific quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) assays confirmed that BTV serotypes 10, 11, 13 and 17 are all present in the region, but that midge infection rates and the number of BTV serotypes circulating differed markedly among the individual farms. Furthermore, more serotypes of BTV were present in midges than in sentinel cattle at individual farms where BTV circulated, and the virus was detected at each farm in midges prior to detection in cattle. BTV infection rates were remarkably lower amongst female C. sonorensis midges collected by CO 2 traps with UV light than among midges collected by either animal-baited aspirations or in CO 2 traps without light. A subsample of female midges examined from each collection method showed no overall differences in the proportion of female midges that had previously fed on a host. Findings from this study confirm the importance of using sensitive 3 surveillance methods for both midge collection and virus detection in epidemiological studies of BTV infection, which is especially critical if the data are to be used for development of mathematical models to predict the occurrence of BTV infection of livestock.

Bluetongue virus (BTV) is the cause of bluetongue (BT), an emerging, arthropod-transmitted disease of ungulates. The cellular tropism of BTV in ruminants includes macrophages, dendritic cells and endothelial cells (EC), and fulminant infection is characterized by lesions consistent with those of so-called viral hemorrhagic fevers. Specifically, BT is characterized by vascular injury with hemorrhage, tissue infarction and widespread edema. To further investigate the pathogenesis of vascular injury in BT, we evaluated the responses of cultured bovine pulmonary artery EC (bPAEC) and monocyte -derived macrophages (bMDM) to BTV infection by measuring transcript levels of genes encoding molecules important in mediating EC activation and/or endothelial barrier dysregulation. The data confirm that BTV infection of bPAEC resulted in increased transcription of genes encoding chemokine ligand 2 (CCL2) and E-selectin, and BTVinfection of bMDM resulted in increased transcription of genes encoding TNF-α, IL-1β, IL-8, and inducible nitric oxide synthase (iNOS). The data from these in vitro studies provide further evidence that cytokines and other vasoactive substances produced in macrophages potentially contribute to vascular injury in BTV-infected ruminants, along with direct effects of the virus itself on ECs.