Lagoviruses

RHD is caused by a lagovirus, which is a genus of viruses in the family Caliciviridae. Other diseases caused by caliciviruses include cat ‘flu (feline calicivirus) and gastroenteritis in humans (norovirus). Caliciviruses are single-stranded RNA viruses. They cannot be grown in tissue culture and are stable in the environment.

RHDV1 (‘Classic’ RHDV)

After the discovery of RHDV in 1984, many strains and variants of the virus were discovered. These are divided into genogroups (G1-G6). The G6 genogroup is also known as RDHVa. RHDV1 only affects the European rabbit (Oryctolagus cuniculus).

European Brown Hare Syndrome virus (EBHSV)

European Brown Hare Syndrome (EBHS) was first described in 1980 and shares many clinical features with rabbit haemorrhagic disease. The virus that causes European Brown Hare Syndrome (EBHSV) is a calicivirus belonging to the Lagovirus genus that generally affects hares. It does not affect the domestic rabbit (Oryctolagus cuniculus) but there is evidence that cottontails (Sylvilagus floridanus) can be infected (Lavazza et al. 2015).

Non-pathogenic rabbit calicivirus (RCV) and hare calicivirus (HaCV)

Although fatalities from RHD were first reported in 1994, antibodies to RHDV were detected in sera collected before that time. It is believed that non-pathogenic strains of rabbit calicivirus (RCVs) could have been around for decades (Moss et al. 2002). These RCVs are believed to play a part in protecting rabbits from RHD by stimulating antibody production. Investigations in Australia and UK have demonstrated the presence of non-pathogenic strains that co-circulated asymptomatically with RHDV in areas with reduced mortality from RHD (Forrester et al. 2009, Cooke et al. 2018). In Australia, rabbits that live in areas of higher rainfall are more likely to be infected with RCV and therefore have some immunity to RHD (Liu et al.2014).

RHDV2 (RHDVb)

RHDV2 is antigenically and genetically different from previously identified strains of RHDV i.e. it is a different virus. Genetic sequencing of the RHDV2 virus has revealed that it constitutes a new phylogenetic group with 80%–82% identity with other lagoviruses (Le Gall-Reculé et al. 2013) and is more closely related to RCV than RHDV1 (Qi et al. 2019). An important feature of RHDV2 is that it can affect hares, including the Sardinian Cape Hare (Lepus capensis mediterraneus), Italian Hare (Lepus corsicanus), Mountain Hare (Lepus timidus), and European Brown Hare (Lepus europaeus) (Le Gall-Reculé et al. 2017, Neimanis, 2018).