The Australian Public is Still Vulnerable to Emerging Virulent Strains of West Nile Virus

Abstract

The mosquito-borne West Nile virus (WNV) is responsible for outbreaks of viral encephalitis in humans and horses with particularly virulent strains causing recent outbreaks in Eastern Europe, the Middle East, and North America. In Australia, a strain of WNV, Kunjin (WNVKUN), is endemic in the north and infection with this virus is generally asymptomatic. However, in early 2011, following extensive flooding, an unprecedented outbreak of WNVKUN encephalitis in horses occurred in South-Eastern Australia, resulting in more than 1,000 cases and a mortality of 10–15%. Despite widespread evidence of equine infections, there was only a single mild human case reported during this outbreak. To understand why clinical disease was seen in horses without similar observations in the human population, a serosurvey was conducted using blood donor samples from areas where equine cases were reported to assess level of flavivirus exposure. The seroprevalence to WNVKUN in humans was low before the outbreak (0.7%), and no significant increase was demonstrated after the outbreak period (0.6%). Due to unusual epidemiological features during this outbreak, a serosurvey was also conducted in rabbits, a potential reservoir host. Out of 675 animals, sampled across Australia between April 2011 and November 2012, 86 (12.7%) were seropositive for WNVKUN, with the highest prevalence during February of 2012 (28/145; 19.3%). As this is the first serological survey for WNVKUN in Australian feral rabbits, it remains to be determined whether wild rabbits are able to develop a high enough viremia to actively participate in WNV transmission in Australia. However, they may constitute a sentinel species for arbovirus activity, and this is the focus of on-going studies. Collectively, this study provides little evidence of human exposure to WNVKUN during the 2011 outbreak and indicates that the Australian population remains susceptible to the emergence of virulent strains of WNV.

Structural and Functional Characterization of Programmed Ribosomal Frameshift Signals in West Nile Virus Strains Reveals High Structural Plasticity Among cis-Acting RNA Elements

“…Whereas NS1 plays an essential role in viral replication and assembly, NS1Ј is not essential. However, in addition to serving the same function as NS1, it has effects on WNV virulence: abrogation of NS1Ј production reduces neuroinvasiveness (10), viral replication, and RNA levels (11,12). The primary translational product is a polyprotein that is subsequently cleaved into structural (encoded by sequences in the 5Ј region of the genome) and NS (encoded downstream sequence) proteins ( Fig.…”

“…Kunjin (accession number AY274504) has caused outbreaks of disease in human and equine populations in Australia. It was previously believed to be a unique species, but now occupies its own clade within lineage 1 of WNV (12). The Madagascar strain (accession number DQ176636) caused an outbreak of disease in birds in 1978, but does not produce appreciable pathogenesis in humans (13).…”

Detection of emergent strains of West Nile virus with a blood screening assay

“…Exposure to WNV KUN is likely to offer protection against WNV infection; however, given the low number of notifications each year and low seroprevalence in NSW blood donor populations, much of the Australian population is likely to be potentially susceptible to WNV were it to become introduced and/or established in Australia. Endemic Australian mosquitos are capable of transmitting WNV, and a number of Australian bird species have the potential to be infected with WNV .…”

“…It is known that WNV can be transmitted by transfusion, WNV KUN is circulating in Australia, Australian blood donors have been exposed to WNV KUN , there is high genetic diversity in the WNV genome, and virulent forms of the virus are known to emerge . Given this, knowledge of whether commercially available WNV NAT blood screening assays can detect different strains of WNV KUN , including the more virulent WNV NSW2011 , is needed.…”

Investigation of neuropathogenesis and control of an equine-pathogenic Australian West Nile virus isolate in an established CD1 Swiss white mouse and a novel rabbit model

“…An initial screen for flavivirus specific antibodies was performed on plasma/sera obtained from NZWR rabbits at termination by a 4G2 pan-flavivirus blocking ELISA [279,280].…”