Host and Potential Vector Susceptibility to an Emerging Orbivirus in the United States: Epizootic Hemorrhagic Disease Virus Serotype 6

Authors: Ruder, Mark; STALLKNECHT, DAVID - University Of Georgia; ALLISON, ANDREW - Cornell University; MEAD, DANIEL - University Of Georgia; CARTER, DEBORAH - University Of Georgia; HOWERTH, ELIZABETH - University Of Georgia

Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2015
Publication Date: 5/1/2016
Citation: Ruder, M.G., Stallknecht, D.E., Allison, A.B., Mead, D.G., Carter, D.L., Howerth, E.W. 2016. Host and Potential Vector Susceptibility to an Emerging Orbivirus in the United States: Epizootic Hemorrhagic Disease Virus Serotype 6. Veterinary Pathology. 53(3):574-584.

Interpretive Summary: Epizootic hemorrhagic disease (EHD) is an important viral disease of white-tailed deer and occasionally cattle, and is transmitted to animals by the bite of infected insects known as Culicoides biting midges. Two different serotypes of EHDV, EHDV-1 and EHDV-2, have been circulating between ruminants (like deer and cattle) and Culicoides biting midges in the United States for over 60 years; however, in 2006 a new serotype (EHDV-6) was documented and since that time this emerging virus has caused death of infected white-tailed deer from the eastern United States. In this study, our goal was to determine the outcome of infection in white-tailed deer, cattle, and an insect vector, Culicoides sonorensis, with EHDV-6 since these are important hosts for the EHD viruses that have circulated in the U.S. for a long time. Findings of the study indicate both white-tailed deer and cattle can become infected with EHDV-6. Deer became severely ill, whereas cattle showed no symptoms. Additionally, Culicoides sonorensis supported virus replication although additional research is needed to confirm this species is capable of transmitting the virus to cattle and deer. The introduction and subsequent establishment of this exotic virus in the U.S. is significant and additional field and laboratory studies are needed to better understand the epidemiology of this emerging virus.

Technical Abstract: Epizootic hemorrhagic disease (EHD) viruses (EHDV) are orbiviruses transmitted by Culicoides biting midges to domestic and wild ruminants. EHDV-1 and -2 are enzootic in the U.S., where EHD is the most significant viral disease of white-tailed deer (WTD; Odocoileus virginianus) and reports of EHD in cattle appear to be increasing. In 2006, a novel reassortant EHDV-6 was isolated from dead WTD in Indiana and has been detected each subsequent year over a wide geographic region. Since EHDV-6 is not a historically endemic serotype in the U.S., it is important to understand the outcome of infection in potential hosts. Specifically, we aimed to evaluate the pathogenicity of the virus in two primary U.S. ruminant hosts (WTD and cattle), as well as the susceptibility of a proven vector of EHDV in the U.S. (Culicoides sonorensis). Five WTD and four Holstein cattle were inoculated with >106 median tissue culture infective doses (TCID50) EHDV-6 by intradermal and subcutaneous injection. All five WTD exhibited moderate to severe disease and three animals died or were euthanized. Viremia was first detected 3-5 days post-infection (dpi) with surviving animals seroconverting by 10 dpi. The observed disease was consistent with previous EHD reports. Two of four cattle had a detectable viremia, 5-10 dpi and 7-24 dpi, respectively. No clinical or hematologic abnormalities were observed. Seroconversion occurred by 10 dpi, although one animal failed to seroconvert. Colonized C. sonorensis were fed on WTD blood spiked with >106 TCID50/ml EHDV-6 and held for 4-14 days post-feeding (dpf) at 22°C. From 4-14 dpf, 11% (19/171) of midges were virus isolation positive and 4% (6/171) had a high virus titer (=102.7 TCID50). While the observed outcomes were variable, these studies demonstrate the susceptibility of ruminant and vector hosts in the U.S. for this recently emerged EHDV serotype.