Rabbit Haemorrhagic Disease (RHD) emerged in the 1980s and is thought to have spread across various wild rabbit populations asymptomatically, until a first symptomatic outbreak was reported in China in 1984. During this initial outbreak, the disease revealed its lethal extent, killing an estimated 14 million domesticated rabbits in China within nine months.
RHD only affects the Oryctolagus cuniculus (European or common rabbit) species and its symptoms include high fever, internal bleeding and liver disease. It is caused by Rabbit Haemorrhagic Disease virus (RHDV), a single-stranded RNA virus in the Caliciviridae family belonging to the Lagovirus genus. In new research published in Veterinary Research, Ghislaine Le Gall-Reculé from the French Agency for Food, Environmental and Occupational Health and Safety, France and colleagues report a new Lagovirus strain, designated RHDV2, which is related to RHDV but with several key differences.
RHDV has proven to be highly infectious and very resistant, even persisting in frozen conditions. The worldwide prevalence of RHDV, as well as the high lethality of the disease, have resulted in intensive vaccination and epidemiological surveillance programmes. Following reports of RHD in rabbitries and among wild rabbit populations in the north-west of France, the authors used RT-PCR analysis and sandwich ELISA testing to confirm that RHDV2 was the aetiological agent responsible. The virus had killed 25 percent of RHDV-vaccinated does in one particular rabbitry.
RHDV2 differs from RHDV and the previously identified RHDVa strain, in several ways. The authors looked at complete sequences of the protein capsid genes to identify the phylogenetic relationship between the strains. They found that RHDV2, though a member of the same genus as RHDV and RHDVa, is phylogenetically distinct from these strains and forms a new genetic group.
Further molecular analysis and experimental studies carried out by the authors revealed a unique antigenic and symptomatic profile for RHDV2. Though less virulent and with lower observed mortality rates than RHDV and RHDVa, the disease resulting from RHDV2 is longer in duration and will take a chronic or subacute course more often than for RHD caused by the other viral strains.
The identification of RHDV2 and the wide range of molecular, experimental infection and epidemiological data presented by the authors represent a significant contribution to our knowledge of RHD and will likely inform epidemiological surveillance efforts in a number of territories.