Insights into the evolution of the new variant rabbit haemorrhagic disease virus (GI.2) and the identification of novel recombinant strains.

Rabbit haemorrhagic disease (RHD) is a viral disease that affects the European rabbit. RHD was detected in 1984 in China and rapidly disseminated worldwide causing a severe decline in wild rabbit populations. The aetiological agent, rabbit haemorrhagic disease virus (RHDV), is an RNA virus of the family Caliciviridae, genus Lagovirus. Pathogenic (G1-G6 or variants GI.1a-GI.1d) and non-pathogenic strains (GI.4) have been characterized. In 2010, a new variant of RHDV, RHDV2/RHDVb/GI.2, was detected in France. GI.2 arrived to the Iberian Peninsula in 2011, and several recombination events were reported. Here, we sequenced full genomes of 19 samples collected in Portugal between 2014 and 2016. New GI.2 recombinant strains were detected, including triple recombinants. These recombinants possess a non-structural protein p16 related to a non-pathogenic strain. Evolutionary analyses were conducted on GI.2 VP60 sequences. Estimated time to the most recent common ancestor (tMRCA) suggests an emergence of GI.2 in July 2008, not distant from its first detection in 2010. This is the first study on GI.2 evolution and highlights the need of continued monitoring and characterization of complete genome sequences when studying lagoviruses' evolution.

Epidemiology of RHDV2 (Lagovirus europaeus/GI.2) in free-living wild European rabbits in Portugal.

As the detection of the first outbreak of a novel aetiological agent of rabbit haemorrhagic disease commonly called RHDV2 or RHDVb (Lagovirus europaeus/GI.2, henceforth GI.2) in France in 2010, the virus rapidly spread throughout continental Europe and nearby islands such as Great Britain, Sardinia, Sicily, the Azores and the Canary Islands among others. The outbreaks of this new lagovirus cause important economic losses in rabbitries, and ecological disruptions by affecting the conservation of rabbit-sensitive top predators. We analysed 550 rabbit carcasses collected in the field between May 2013 and March 2016, to investigate the epidemiology of GI.2 in free-living populations and to perform a comparative analysis with the epidemiology of classical rabbit haemorrhagic disease virus forms (RHDV, henceforth GI.1) in Portugal. Rabbits were sexed, aged and liver and blood samples were collected for subsequent RHDV screening and serology. A total of 172 samples were PCR-positive to GI.2, whereas GI.1 strains were not detected in any of the samples. The outbreaks of GI.2 revealed a marked seasonality, with peaks during the breeding season (November-May). We also found that approximately, one-third of free-ranging European rabbits in Portugal have seroconverted to GI.2. We demonstrate that the GI.2 lagovirus is currently widespread in wild populations in Portugal and is affecting a high proportion of adults and juveniles. Therefore, ongoing monitoring and surveillance are required to assess the effects of GI.2 on wild rabbit populations, its evolution, and to guide management actions aimed at mitigating the impacts of rabbit declines in the ecosystem and in rural economies.