Since summer 2010, numerous cases of Rabbit Haemorrhagic Disease (RHD) have been reported in north-western France both in rabbitries, affecting RHD-vaccinated rabbits, and in wild populations. We demonstrate that the aetiological agent was a lagovirus phylogenetically distinct from other lagoviruses and which presents a unique antigenic profile. Experimental results show that the disease differs from RHD in terms of disease duration, mortality rates, higher occurrence of subacute/chronic forms and that partial cross-protection occurs between RHDV and the new RHDV variant, designated RHDV2. These data support the hypothesis that RHDV2 is a new member of the Lagovirus genus. A molecular epidemiology study detected RHDV2 in France a few months before the first recorded cases and revealed that one year after its discovery it had spread throughout the country and had almost replaced RHDV strains. RHDV2 was detected in continental Italy in June 2011, then four months later in Sardinia.

Rabbit haemorrhagic disease virus (RHDV) is a lagovirus that causes rabbit haemorrhagic disease (RHD) in European rabbits (Oryctolagus cuniculus). In 2010, a new genotype called RHDV2 emerged in France. It exhibits a larger host range than classical RHDV strains by sporadically infecting different hare species, including the European hare (Lepus europaeus). Phylogenetic analyses revealed that closely related RHDV2 strains circulate locally in both hares and rabbits, and therefore that RHDV2 strains infecting hares do not belong to a lineage that has evolved only in this species. We showed that RHDV2 is widely distributed in France and that it was responsible for more than a third of cases of lagovirus disease in European hare populations in 2015. The oldest RHDV2 positive hare was sampled in November 2013 and we reported two hares co-infected by EBHSV and RHDV2. All together, our results raise important epidemiological and evolutionary issues. In particular, along with the potential emergence of recombinant EBHSV/RHDV2 strains in hares, the enlargement of the host range changes the host population structure of RHDV2 and may alter the impact of the virus on rabbit and hare populations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-017-0473-y) contains supplementary material, which is available to authorized users.

Rabbit haemorrhagic disease is a viral disease that emerged in the 1980s and causes high mortality and morbidity in the European rabbit (Oryctolagus cuniculus). In 2010, a new genotype of the rabbit haemorrhagic disease virus emerged and replaced the former circulating Lagovirus europaeus/GI.1 strains. Several recombination events have been reported for the new genotype Lagovirus europaeus/ GI.2, with pathogenic (variants GI.1a and GI.1b) and benign (genotype GI.4) strains that served as donors for the non-structural part while GI.2 composed the structural part; another recombination event has also been described at the p16/p23 junction involving GI.4 strains. In this study, we analysed new complete coding sequences of four benign GI.3 strains and four GI.2 strains. Phylogenetic and recombination detection analyses revealed that the first GI.2 strains, considered as non-recombinant, resulted from a recombination event between GI.3 and GI.2, with GI.3 as the major donor for the nonstructural part and GI.2 for the structural part. Our results indicate that recombination contributed to the emergence, persistence and dissemination of GI.2 as a pathogenic form and that all described GI.2 strains so far are the product of recombination. This highlights the need to study full-genomic sequences of lagoviruses to understand their emergence and evolution. Since the 1980s, European rabbits worldwide, either domestic or wild, have been affected by rabbit haemorrhagic disease 1. This highly contagious and fatal disease is caused by the rabbit haemorrhagic disease virus (RHDV), a single-stranded positive-sense RNA virus that belongs to the family Caliciviridae, genus Lagovirus. Benign rabbit caliciviruses that confer more or less protection against pathogenic strains, as well as moderately pathogenic strains, including Michigan rabbit calicivirus (MRCV), have also been described 2-7. In 2010, a new pathogenic lagovirus was identified in France 8 , formerly designated as RHDV2 or RHDVb and now as Lagovirus europaeus/GI.2 according to a proposal for a unified nomenclature for lagoviruses 9. GI.2 caused unusual mortalities in rabbits vaccinated against GI.1 (former G1-G6) strains 8, 10. Further analysis revealed genetic differences that were reflected in its positioning in a phylogenetic tree based on capsid protein (VP60) sequences. GI.2 constituted a new phylogenetic group 8, 11 with more than 15% divergence from all know benign and pathogenic lagoviruses. Other unique characteristics include its ability to fatally infect rabbits younger than two months (previously resistant to the disease) 11, 12 and several hare species (Lepus spp.) 13-17. Differences in disease duration, mortality rates, and in the frequency of occurrence of subacute/chronic forms have also been