Rabbit haemorrhagic disease virus (RHDV) is a positive-sense RNA virus in the family Caliciviridae. It causes an acute necrotizing hepatitis in European rabbits (Oryctolagus cuniculus) and mortality rates can exceed 90% in susceptible adults. Death often occurs within 72 hours of infection. Overseas, RHDV causes significant economic losses to rabbit meat industries and also has a negative ecological impact, as wild rabbits play a key role in many ecosystems. In contrast, in Australia RHDV is widely used as a biocontrol agent to control feral rabbit populations.
Recently a genetically and antigenically distinct variant of RHDV, designated RHDV2, was reported from European RHDV outbreaks beginning in France in 2010. In contrast to ‘classical’ strains of RHDV, RHDV2 reportedly causes a higher mortality rate in young rabbits that are normally highly resistant to lethal RHDV infection. RHDV2 spreads effectively in domestic rabbits in Europe and may be replacing existing strains of RHDV in wild rabbits on the Iberian Peninsula, most likely due to its ability to partially overcome immunity to ‘classical’ strains. RHDV2 has also been reported to have undergone recombination several times, resulting in viruses with the RHDV2 capsid gene and non-structural genes of a series of genetically diverse rabbit caliciviruses.
In May 2015, RHDV2 was isolated for the first time in Australia. Virus was recovered from a wild rabbit in the ACT as part of ongoing opportunistic surveillance (BlMt-1). Phylogenetic analysis revealed that BlMt-1 was most closely related to a previously reported recombinant RHDV2 circulating in Portugal. This indicates that the origin of this virus is in Europe; how it arrived in Australia however, is unclear.
Increasing monitoring and surveillance of RHDV outbreaks in both wild and domestic Australian rabbits is now urgently required to follow the spread of this new variant or to determine where it is already present.