Dynamics of epizootic hemorrhagic disease virus infection within the vector, Culicoides sonorensis (Diptera: Ceratopogonidae)

PLoS One. 2017 Nov 27;12(11):e0188865. doi: 10.1371/journal.pone.0188865. eCollection 2017.

Abstract

Culicoides sonorensis biting midges are confirmed vectors of epizootic hemorrhagic disease virus (EHDV), which causes mortality in white-tailed deer and ruminant populations. Currently, of the seven EHDV serotypes, only 1, 2, and 6 are detected in the USA, and very few studies have focused on the infection time course of these serotypes within the midge. The objective of this current research was to characterize EHDV-2 infection within the midge by measuring infection prevalence, virus dissemination, and viral load over the course of infection. Midges were fed a blood meal containing 106.9 PFU/ml EHDV-2, collected every 12 h from 0-2 days post feeding (dpf) and daily from 3-10 dpf, and cohorts of 20 C. sonorensis were processed using techniques that assessed EHDV infection and dissemination. Cytopathic effect assays and quantitative (q)PCR were used to determine infection prevalence, revealing a 50% infection rate by 10 dpf using both methods. Using immunohistochemistry, EHDV-2 infection was detectable at 5 dpf, and shown to disseminate from the midgut to other tissues, including fat body, eyes, and salivary glands by 5 dpf. Stain intensity increased from 5-8 dpf, indicating replication of EHDV-2 in secondary infection sites after dissemination. This finding is also supported by trends in viral load over time as determined by plaque assays and qPCR. An increase in titer between 4-5 dpf correlated with viral replication in the midgut as seen with staining at day 5, while the subsequent gradual increase in viral load from 8-10 dpf suggested viral replication in midges with disseminated infection. Overall, the data presented herein suggest that EHDV-2 disseminates via the hemolymph to secondary infection sites throughout the midge and demonstrate a high potential for transmission at five days at 25°C after an infective blood-meal.

MeSH terms

  • Animals
  • Ceratopogonidae / virology*
  • Chironomidae / virology
  • Hemorrhagic Disease Virus, Epizootic / physiology*
  • Immunohistochemistry
  • Insect Vectors / virology*
  • Prevalence
  • Reoviridae Infections / epidemiology*
  • Reoviridae Infections / pathology
  • Reoviridae Infections / virology*
  • Time Factors
  • Tropism
  • Viral Load

Grants and funding

Research reported in this publication was supported by the USDA-ARS National Programs 103 & 104 (B.S.D., D.N.), and through Specific Cooperative Agreement, 58-5430-4-022 (K.M.). Publication of this article was funded in part by the Kansas State University Open Access Publishing Fund. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. Any opinions, findings, conclusion, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. This is contribution 17-393-J from the Kansas Agricultural Experiment Station. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.