Rabbit Hemorrhagic Disease Virus 2 (RHDV2; GI.2) Is Replacing Endemic Strains of RHDV in the Australian Landscape within 18 Months of Its Arrival

Abstract

(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.

A strain‐specific multiplex RT ‐ PCR for Australian rabbit haemorrhagic disease viruses uncovers a new recombinant virus variant in rabbits and hares

“…Interestingly, this recombinant variant was also detected in a hare, suggesting that the GI.2 capsid protein is responsible for permissivity of hare cells to infection. This is further supported by full‐genome sequencing of five GI.2 viruses isolated from European brown hares in Australia, which confirmed that these infections were also due to recombinant GI.2 viruses (GI.1b non‐structural genes, GI.2 structural genes) (Mahar et al., ). This once again highlights the importance of recombination for generating genetic diversity in caliciviruses and indicates the frequency with which new viruses can emerge when genetically diverse lagoviruses circulate concurrently.…”

“…This study utilized rabbit calicivirus strains of the lagovirus GI genogroup, belonging to the variant groups GI.1c, GI.1a, GI.4eP‐GI.1a (GI.1a‐Aus), GI.1bP‐GI.2, GI.4eP‐GI.2 (newly identified in this study), GI.4a, GI.4b and GI.4c, where P denotes the polymerase variant for recombinant viruses (Mahar et al., ).…”

Emerging RHDV2 suppresses the impact of endemic and novel strains of RHDV on wild rabbit populations

“…In 2010 a novel lagovirus, known as RHDV2 (or RHDVb), was discovered in France and has since spread rapidly throughout Europe, replacing existing strains of classical RHDV (Dalton, Nicieza, Abrantes, Esteves, & Parra, ; Le Gall‐Reculé et al, ). RHDV2 was first reported in Australia in May 2015 and spread rapidly, reaching Victoria and South Australia by December 2015 and Western Australia by August 2016 (Mahar et al, ). Laboratory studies using experimental infections with early isolates of RHDV2 indicated that mortality rates due to RHDV2 infection were lower than RHDV, with a longer infectious period (Dalton et al, ; Le Gall‐Reculé et al, ).…”

Retrospective serological analysis reveals presence of the emerging lagovirus RHDV2 in Australia in wild rabbits at least five months prior to its first detection

“…Adaptation of the IgM and IgA ELISA to RHDV2 by using RHDV2 specific antigen and MAb increased the sensitivity of these assays for RHDV2 IgM and IgA detection substantially. While the use of the original RHDV IgA and IgM assays is sufficient to infer broader disease activity patterns in wild rabbit populations for all lagoviruses including RHDV2 (Figure a), switching to these more sensitive assays for future large‐scale field epidemiology studies should be considered if RHDV2 remains the dominant strain in the Australian landscape (Mahar, Hall, et al, ).…”

“…It is not only genetically distinct from RHDV and RHDVa but, unlike RHDV and RHDVa, is also able to cause highly fatal disease in very young rabbits (Dalton, Nicieza, Abrantes, Esteves, & Parra, ; Neimanis, Pettersson, Huang, Gavier‐Widen, & Strive, ) and is capable of fatally infecting several species of hares (Camarda et al, ; Hall et al, ; Le Gall‐Recule et al, ; Neimanis, Ahola, et al, ; Puggioni et al, ; Velarde et al, ). Since its arrival in Australia, RHDV2 has become the dominant strain circulating in the field, seemingly replacing older RHDV strains and accounting for the majority of reported cases in wild and domestic rabbits (Mahar, Hall, et al, ).…”