Lagoviruses belong to the Caliciviridae family. They were first recognized as highly pathogenic viruses of the European rabbit (Oryctolagus cuniculus) and European brown hare (Lepus europaeus) that emerged in the 1970-1980s, namely, rabbit haemorrhagic disease virus (RHDV) and European brown hare syndrome virus (EBHSV), according to the host species from which they had been first detected. However, the diversity of lagoviruses has recently expanded to include new related viruses with varying pathogenicity, geographic distribution and host ranges. Together with the frequent recombination observed amongst circulating viruses, there is a clear need to establish precise guidelines for classifying and naming lagovirus strains. Therefore, here we propose a new nomenclature based on phylogenetic relationships. In this new nomenclature, a single species of lagovirus would be recognized and called Lagovirus europaeus. The species would be divided into two genogroups that correspond to RHDV- and EBHSV-related viruses, respectively. Genogroups could be subdivided into genotypes, which could themselves be subdivided into phylogenetically well-supported variants. Based on available sequences, pairwise distance cutoffs have been defined, but with the accumulation of new sequences these cutoffs may need to be revised. We propose that an international working group could coordinate the nomenclature of lagoviruses and any proposals for revision.

(RHDV2; GI.2) is a pathogenic calicivirus that affects European rabbits () and various hare () species. GI.2 was first detected in France in 2010 and subsequently caused epidemics in wild and domestic lagomorph populations throughout Europe. In May 2015 GI.2 was detected in Australia. Within 18 months of its initial detection GI.2 had spread to all Australian states and territories and rapidly became the dominant circulating strain, replacing (RHDV/GI.1) in mainland Australia. Reconstruction of the evolutionary history of 127 Australian GI.2 isolates revealed that the virus arrived in Australia at least several months before its initial description and likely circulated unnoticed in wild rabbit populations in the east of the continent prior to its detection. GI.2 sequences isolated from five hares clustered with sequences from sympatric rabbit populations sampled contemporaneously, indicating multiple spillover events into hares rather than an adaptation of the Australian GI.2 to a new host. Since the presence of GI.2 in Australia may have wide ranging consequences for rabbit biocontrol, particularly with the release of the novel biocontrol agent GI.1a/RHDVa-K5 in March 2017, ongoing surveillance is critical to understanding the interactions of the various lagoviruses in Australia, and their impact on host populations. This study describes the spread and distribution of (GI.2) in Australia since its first detection in May 2015. Within the first 18 months following its detection, RHDV2 spread from east to west across the continent and became the dominant strain in all mainland states of Australia. This has important implications for pest animal management and for owners of pet and farmed rabbits, as there is currently no effective vaccine available in Australia for GI.2. The closely related RHDV (GI.1) is used to control overabundant wild rabbits, a serious environmental and agricultural pest in this country, and it is currently unclear how widespread circulation of GI.2 will impact ongoing targeted wild rabbit management operations.

Two caliciviruses occur in Australian wild rabbits: rabbit calicivirus Australia 1 (RCV-A1) and rabbit haemorrhagic disease virus (RHDV), which is used in Australia as a biocontrol agent to reduce feral rabbit populations. There is concern that RCV-A1 acts as a natural vaccine and protects from lethal RHDV infection. To investigate this hypothesis, domestic rabbits were perorally infected with RCV-A1, monitored for 28 days and subsequently challenged with RHDV. We show that RCV-A1 causes a non-pathogenic infection and is shed in faeces for up to 7 days post-infection. RCV-A1 was detected in the bile 2 months post-inoculation, indicating a prolonged or possible persistent infection. All animals infected with RCV-A1 developed antibodies cross-reacting to RHDV. When challenged with RDHV, half of the rabbits (n=4) survived the infection. The results indicate that RCV-A1 is likely to persist in rabbit populations and can elicit partial cross-protection to lethal RHDV infection.