Abstract
Female Culicoides sonorensis biting midges are vectors of epizootic hemorrhagic disease virus (EHDV), which causes morbidity and mortality in wild and domesticated ruminants. The aims in this study were to identify key changes in female midge transcriptome profiles occurring during early infection with EHDV-2. Midges were fed either negative control bloodmeals or bloodmeals containing EHDV-2 and transcriptomes were acquired at 36 h through deep sequencing. Reads were de novo assembled into a transcriptome comprised of 18,754 unigenes. Overall, there were 2401 differentially expressed unigenes and ~60% were downregulated in response to the virus (953 up; 1448 down). Downstream Gene Ontology enrichment, KEGG pathway mapping, and manual analyses were used to identify the effect of virus ingestion at both the gene and pathway levels. Downregulated unigenes were predominantly assigned to pathways related to cell/tissue structure and integrity (actin cytoskeleton, adherens junction, focal adhesion, hippo signaling), calcium signaling, eye morphogenesis and axon guidance. Unigenes attributed to sensory functions (especially vision), behavior, learning and memory were largely downregulated. Upregulated unigenes included those coding for innate immune processes, olfaction and photoreceptor pigments. Our results suggest that midges respond to virus infection as soon as 36 h post-ingestion, and that EHDV-2 may have a significant phenotypic effect on sensory and neural tissues.
Highlights
Female Culicoides sonorensis (Wirth and Jones) are vectors of orbiviruses including epizootic hemorrhagic disease virus (EHDV) [1,2]
While 100% of midges collected at 36 h post-ingestion were positive for EHDV-2 by CPE assay, 60% of midges were below the limit of detection (102.3 TCID50 /midge), with quantifiable titers between 102.3 and 102.8
The current study suggests that the virus could be affecting these tissues as soon as 36 h post-ingestion, as indicated by the downregulation of 62 unigenes associated with vision in midges that ingested EHDV-2 compared to controls
Summary
Female Culicoides sonorensis (Wirth and Jones) are vectors of orbiviruses including epizootic hemorrhagic disease virus (EHDV) [1,2]. In the USA, EHDV causes moderate to severe disease in ruminants, and can be especially pathogenic to captive and wild cervids, such as white-tailed deer in non-endemic areas [3,4,5]. Of the seven serotypes of EHDV, EHDV-1, -2 and -6 are endemic in the USA, and EHDV-1 and -2 have been associated with cyclical disease outbreaks in ruminants for over 60 years [1]. Collected during a 2012 epidemic of hemorrhagic disease in wild ruminants (e.g., white-tailed deer) in the Midwestern region of the USA demonstrated that the responsible serotypes were EHDV-2 and EHDV-6 [1]. Factors underlying vector competence for EHDV have not been elucidated, but likely include physical barriers (e.g., peritrophic matrix and midgut tissues) as well as immune-mediated defenses, such as innate immune responses and siRNA pathways (reviewed in [10])
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