The Changing Epidemiology of Kunjin Virus in Australia

Natalie Prow

doi:10.3390/ijerph10126255

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.

Highlights

West Nile virus (WNV) has emerged as a global public health concern, causing large outbreaks in the Americas, Europe and more recently Australia [1,2,3,4,5,6,7,8,9]
This review summarizes our current understanding of WNVKUN and how the epidemiology and ecology of this virus has changed
A large number of serological samples that were confirmed as flavivirus positive could not be clearly identified as Murray Valley encephalitis virus (MVEV) or WNVKUN due to inconclusive findings during the analysis. These results suggest a need for re-evaluation of current diagnostic tests for MVEV and WNVKUN in the context of currently circulating virus strains

Summary

Introduction

West Nile virus (WNV) has emerged as a global public health concern, causing large outbreaks in the Americas, Europe and more recently Australia [1,2,3,4,5,6,7,8,9]. Kunjin virus (WNVKUN) is classified within a clade of the WNV group and has traditionally been associated with mild and rare disease in humans and horses in Australia. Phylogenetic analysis has suggested that WNV emerged in Africa and can be separated into at least seven genetic lineages [10]. There are two main lineages (I and II), with lineage I containing WNVKUN isolates and WNV isolates from North, West and Central Africa; southern and eastern Europe; the Middle East; and New York. Following extensive flooding across Eastern Australia in 2011 promoting ideal conditions for freshwater mosquito breeding, an unprecedented outbreak of equine encephalitis occurred, leading to the isolation of the first virulent strain of WNVKUN to cause a major outbreak, designated WNVNSW2011 [2]

Results

Discussion

Conclusion