Virulence and Evolution of West Nile Virus, Australia, 1960-2012

• Published in: Emerging infectious diseases Vol. 22; no. 8; pp. 1353 - 1362
• Main Authors: Prow, Natalie A, Edmonds, Judith H, Williams, David T, Setoh, Yin X, Bielefeldt-Ohmann, Helle, Suen, Willy W, Hobson-Peters, Jody, van den Hurk, Andrew F, Pyke, Alyssa T, Hall-Mendelin, Sonja, Northill, Judith A, Johansen, Cheryl A, Warrilow, David, Wang, Jianning, Kirkland, Peter D, Doggett, Stephen, Andrade, Christy C, Brault, Aaron C, Khromykh, Alexander A, Hall, Roy A
• Format: Journal Article
• Language: English
• Published: United States Centers for Disease Control and Prevention 01-08-2016
• Subjects: Amino Acid Sequence; Animals; Antibodies, Monoclonal; Antibody Specificity; Antigens, Viral - genetics; Australia; Australia - epidemiology; Cell Line; encephalitis; Evolution, Molecular; evolutionary markers; Genome, Viral; Humans; Mice; Virulence; Virulence and Evolution of West Nile Virus, Australia, 1960–2012; viruses; West Nile Fever - epidemiology; West Nile Fever - virology; West Nile virus; West Nile virus - genetics; West Nile virus - pathogenicity; viruses; vector-borne infections; virulence; encephalitis; West Nile virus; evolutionary markers; zoonoses; Australia; flavivirus
• ISSN: 1080-6040; 1080-6059
• DOI: 10.3201/eid2208.151719

Worldwide, West Nile virus (WNV) causes encephalitis in humans, horses, and birds. The Kunjin strain of WNV (WNVKUN) is endemic to northern Australia, but infections are usually asymptomatic. In 2011, an unprecedented outbreak of equine encephalitis occurred in southeastern Australia; most of the ≈900 reported cases were attributed to a newly emerged WNVKUN strain. To investigate the origins of this virus, we performed genetic analysis and in vitro and in vivo studies of 13 WNVKUN isolates collected from different regions of Australia during 1960-2012. Although no disease was recorded for 1984, 2000, or 2012, isolates collected during those years (from Victoria, Queensland, and New South Wales, respectively) exhibited levels of virulence in mice similar to that of the 2011 outbreak strain. Thus, virulent strains of WNVKUN have circulated in Australia for >30 years, and the first extensive outbreak of equine disease in Australia probably resulted from a combination of specific ecologic and epidemiologic conditions.