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 (WNVKUN), 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 (WNVNSW2011) was isolated and found to be most closely related to the indigenous WNVKUN, 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 (WNVNY99) compared to the prototype WNVKUN were present in the WNVNSW2011 sequence. This review summarizes our current understanding of WNVKUN and how the epidemiology and ecology of this virus has changed. Analysis of virulence determinants of contemporary WNVKUN 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.

Figure 1

Location of sentinel chicken flocks around Australia, 2010–2011, Adapted from CDI Annual Report Vol. 37 No. 1 2013, used by permission of the Australian Government [26]. Australian states are shown in red. WA—Western Australia, NT—Northern Territory, QLD—Queensland, NSW—New South Wales, VIC—Victoria, TAS—Tasmania. Blue box represents the Kimberley region and the red box the Pilbara region. Inset represents sentinel chicken flocks in Victoria and New South Wales.

Figure 2

Historical distribution of WNV_KUN in Australia (A). Distribution of encephalitic horse cases in NSW during the 2011 outbreak (B). Dashed line indicates the Great Dividing Range. Adapted from [2].

Figure 3

Distribution of horse cases during the 2011 outbreak. Adapted from [45].