Evaluation of 2012 US EHDV-2 outbreak isolates for genetic determinants of cattle infection

Authors: Schirtzinger, Erin; Jasperson, Dane; RUDER, MARK - University Of Georgia; STALLKNECHT, DAVID - University Of Georgia; CHASE, CHRISTOPHER - South Dakota State University; JOHNSON, DONNA - Animal And Plant Health Inspection Service (APHIS); OSTLUND, EILEEN - Animal And Plant Health Inspection Service (APHIS); Wilson, William

Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2018
Publication Date: 3/14/2019
Citation: Schirtzinger, E.E., Jasperson, D.C., Ruder, M.G., Stallknecht, D.E., Chase, C.C., Johnson, D.J., Ostlund, E.N., Wilson, W.C. 2019. Evaluation of 2012 US EHDV-2 outbreak isolates for genetic determinants of cattle infection. Journal of General Virology. 100:556-567.

Interpretive Summary: Following a summer of severe drought and abnormally high temperatures, a large outbreak of EHDV occurred during 2012 in the US. Of the three serotypes of EHDV circulating during the outbreak, EHDV-2 was most frequently detected. As often seen in EHDV outbreaks, large numbers of white-tailed deer became sick and died. The unusual thing about the 2012 outbreak was that in the Midwest and northern Plains cattle were also becoming sick with EHDV. This study looks at the genomic sequences of EHDV-2 viruses isolated from sick cattle and compares them with recent and historical EHDV-2 sequences to determine if the outbreak viruses had new mutations that enabled them to infect cattle and cause disease. Our results show that of the ten segments of the EHDV genome only two showed unique genetic mutations specific to the 2012 outbreak viruses. A 2012 virus isolated from a white-tailed deer also shares these genetic mutations suggesting that the viruses isolated from sick cattle are not unique and environmental variables such as severe drought, high temperatures, increased exposure to biting midges due to a reduced number of water sources, etc may be to blame for the severity of the 2012 outbreak.

Technical Abstract: Following a summer of severe drought and abnormally high temperatures, a large outbreak of EHDV occurred during 2012 in the US. Although EHDV-1, -2 and -6 were isolated, EHDV-2 was the predominant outbreak serotype. In addition to large losses of white-tailed deer, the Midwest and northern Plains saw a significant amount of clinical disease in cattle. Phylogenetic analyses and sequence comparisons of newly sequenced whole genomes of 2012 EHDV-2 cattle isolates show that eight of ten EHDV-2 genomic segments show no genetic changes that separate the cattle outbreak sequences from other EHDV-2 isolates. Two segments, VP2 and VP6 did show several unique genetic changes specific to the 2012 cattle outbreak isolates, although the impact of the genetic changes on viral fitness is unknown. The placement of isolates from 2007 and 2011 as sister group to the outbreak isolates and the similarity between cattle and deer isolates point to environmental variables as having a greater influence on the severity of the 2012 EHDV outbreak than genetic changes.