The Changing Epidemiology of Kunjin Virus in Australia

Abstract

West Nile virus (WNV) is a mosquito-borne virus responsible for outbreaks of viral encephalitis in humans and horses, with particularly virulent strains causing recent outbreaks of disease in Eastern Europe, the Middle East and North America. A strain of WNV, Kunjin (WNV _KUN), is endemic in northern Australia and infection with this virus is generally asymptomatic. However in early 2011, an unprecedented outbreak of encephalitis in horses occurred in south-eastern Australia, resulting in mortality in approximately 10%–15% of infected horses. A WNV-like virus (WNV _NSW2011) was isolated and found to be most closely related to the indigenous WNV _KUN, rather than other exotic WNV strains. Furthermore, at least two amino acid changes associated with increased virulence of the North American New York 99 strain (WNV _NY99) compared to the prototype WNV _KUN were present in the WNV _NSW2011 sequence. This review summarizes our current understanding of WNV _KUN and how the epidemiology and ecology of this virus has changed. Analysis of virulence determinants of contemporary WNV _KUN isolates will provide clues on where virulent strains have emerged in Australia. A better understanding of the changing ecology and epidemiology associated with the emergence of virulent strains is essential to prepare for future outbreaks of WNV disease in Australia.