Melinda J. Frost 1 , Jing Zhang 1 , Judith H. Edmonds 1 , Natalie A. Prow 1 , Xingnian Gu , Rodney Davis , Christine Hornitzky , Kathleen E. Arzey , Deborah Finlaison , Paul Hick , Andrew Read , Jody Hobson-Peters , Fiona J. May , Stephen L. Doggett , John Haniotis , Richard C. Russell , Roy A. Hall 2 , Alexander A. Khromykh 2 , Peter D. Kirkland , 2
An encephalitis outbreak among horses was caused by a pathogenic variant of Kunjin virus.
To determine the cause of an unprecedented outbreak of encephalitis among horses in New South Wales, Australia, in 2011, we performed genomic sequencing of viruses isolated from affected horses and mosquitoes. Results showed that most of the cases were caused by a variant West Nile virus (WNV) strain, WNV NSW2011, that is most closely related to WNV Kunjin (WNV KUN), the indigenous WNV strain in Australia. Studies in mouse models for WNV pathogenesis showed that WNV NSW2011 is substantially more neuroinvasive than the prototype WNV KUN strain. In WNV NSW2011, this apparent increase in virulence over that of the prototype strain correlated with at least 2 known markers of WNV virulence that are not found in WNV KUN. Additional studies are needed to determine the relationship of the WNV NSW2011 strain to currently and previously circulating WNV KUN strains and to confirm the cause of the increased virulence of this emerging WNV strain.