Exploring the susceptibility of North American ruminant and vector hosts to an exotic epizootic hemorrhagic disease virus, (EHDV-7)
Ruder, Mark Gregory
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Epizootic hemorrhagic disease (EHD) viruses (EHDV) are significant pathogens of North American wild ruminants, namely white-tailed deer (WTD; Odocoileus virginianus), and along with bluetongue viruses (BTV), cause hemorrhagic disease (HD) of deer. Historically, infection of cattle with EHDV primarily has been considered subclinical, or rarely associated with mild disease. However, over the past decade reports of EHD in cattle have increased in some parts of the world. During 2006 in Israel, EHDV-7 caused an intense and widespread epizootic in cattle that financially impacted the Israeli dairy industry. The susceptibility of potential North American vector and ruminant hosts to infection with EHDV-7 is not known. Our specific research objectives were to: 1) determine whether WTD and 2) cattle are susceptible to infection with EHDV-7, 3) evaluate Culicoides sonorensis, a confirmed vector of EHDV in North America, as a potential vector of this exotic virus, and 4) examine the effect of ambient temperature on replication of EHDV in C. sonorensis. Cattle, WTD, and C. sonorensis were experimentally infected with EHDV-7 and our findings indicate that WTD are susceptible to infection and disease, whereas cattle were subclinically infected. Additionally, C. sonorensis transmitted EHDV-7 between WTD, proving this species is a competent vector of this exotic orbivirus. Furthermore, we demonstrated that replication of EHDV-1, -2, and -7 is temperature-dependent in C. sonorensis. Collectively, these results indicate that WTD and cattle are susceptible to EHDV-7 infection and North America harbors a potential vector. Two fundamental requirements for a vector-borne pathogen to become established in a new ecosystem following its introduction are the presence of 1) a susceptible host, and 2) a competent vector. Although, many additional environmental, host, and vector factors would be required for establishment, our findings indicate that our North American vector-host system is susceptible to EHDV-7. The mortality observed during the WTD trial reaffirms the utility of this species as a sentinel for EHDV activity, both endemic and non-endemic. Further, the clinical similarities observed in the WTD study with disease caused by endemic EHDV and BTV serotypes highlight the importance of serotype-specific diagnostics during the investigation of suspected HD outbreaks.