Recombination between non-structural and structural genes as a mechanism of selection in lagoviruses: The evolutionary dead-end of an RHDV2 isolated from European hare

Detection of a New Recombinant Rabbit Hemorrhagic Disease Virus 2 in China and Development of Virus-like Particle-Based Vaccine

Rabbit hemorrhagic disease virus (RHDV) is a very virulent virus of the genus Lagovirus causing severe and fatal hepatitis in the European rabbit (Oryctolagus cuniculus). RHDV has two distinct genotypes: GI.1 (RHDV) and GI.2 (RHDV2). The first RHDV2/GI.2 strain was identified as a recombinant virus between a non-pathogenic (GI.3P) and a pathogenic (GI.2) lagovirus, and the recombination is thought to have been a key mechanism in the emergence and evolution of RHDV2. Here, a new variant of RHDV2 was identified affecting domestic rabbits on Chinese farms, with a mortality rate of 70-80%. Phylogenetic analysis indicated that the nonstructural portion of this newly identified strain's genome clustered with the GI.1a variants. In contrast, the capsid gene shared the highest nucleotide identity of 97.9% with the North American GI.2 strains, suggesting a possible introduction in China of North American strains and recombination with the GI.1a strains circulating in China. We have produced a recombinant vaccine using the first Chinese GI.2 strain, SC2020/0401, by cloning the vp60 gene into a baculovirus expression vector. Virus-like particles (VLPs) were then produced in Sf9 insect cells, and a challenge study was performed. Rabbits immunized with the VLP vaccine survived 7 d after being challenged with the new virus. The results indicate that commercial vaccines are urgently required in China to control the circulation of RHDV2 variants.

Pathological and serological insights into Lagovirus diseases dynamics in the European brown hare (Lepus europaeus): A nine-year longitudinal study

The European brown hare syndrome virus (EBHSV; GII.1) and rabbit haemorrhagic disease virus 2 (RHDV2; GI.2) are pathogenic lagoviruses affecting the European brown hare (Lepus europaeus). EBHSV/GII.1 causes periodic epidemics, while RHDV2/GI.2 infections emerge from spillover events in areas where hares are sympatric with European rabbits (Oryctolagus cuniculus). In the northeast of the Iberian Peninsula, the overlap of these species provides a unique opportunity to investigate how the epidemiology of these viruses correlates with disease course. We analysed the presence of lagoviruses in 113 European brown hare carcasses recovered in Catalonia (NE Spain) between 2015 and 2024. Animals were necropsied, and tissue and serum samples were collected for histopathology, virological investigation, and serology. Sera from hunted hares apparently healthy (n = 89, 2015-2023) were also included in the study. PCR on liver samples (n = 58) and virological ELISA on positive sera (n = 52) confirmed 28 EBHSV/GII.1 and 24 RHDV2/GI.2 cases. After the first EBHSV/GII.1 detection in 2016, antibody titres decreased progressively until 2020-2021, coinciding with an outbreak. No conclusive seropositivity for RHDV2/GI.2 was observed during the study. Pathology revealed more acute lesions in RHDV2/GI.2-infected hares compared to EBHSV/GII.1. These lesions, resulting in sudden death due to a deficient immune response, may explain this distinct epidemiological scenario. Despite a decade of circulation, RHDV2/GI.2 has not fully adapted to hares. However, ongoing monitoring is essential, as mutations or recombination events could increase its epizootic potential. The co-circulation of both lagoviruses, combined with other co-factors, might jeopardise the viability of European brown hare populations at the southern limit of their range.

Two decades of occurrence of non-pathogenic rabbit lagoviruses in Italy and their genomic characterization

Lagoviruses are viruses of the Caliciviridae family affecting lagomorphs. Both pathogenic and non-pathogenic lagoviruses affect the European rabbit (Oryctolagus cuniculus), and they are phylogenetically distinguished. Rabbit Hemorrhagic Disease Virus (RHDV/GI.1) and Rabbit Hemorrhagic Disease Virus-2 (RHDV-2/GI.2) belong to the first group, while in the second group, several genotypes of Rabbit Calicivirus (RCV/GI.3-GI.4) are present. The first RCV strain was described in Italy in 1996, and since then, several RCV strains have been characterised in Europe and Australia. RCVs, different from the pathogenic hepatotropic RHDVs, have an enteric tropism and could be identified from the duodenum/intestine and faeces. This study aimed firstly to indirectly show through a seroepidemiological survey from 1998 to 2008 the circulation of RCVs strains in rabbit farms and then to genetically characterise RCV strains diagnosed in Italy in faecal and intestinal samples of wild and farmed rabbits collected in various regions in the following years (2000-2022). Of 262 analysed samples, 69 resulted in RT-PCR positive for lagovirus but negative for RHDV. Eleven RCV strains were characterised by complete vp60 sequencing. Phylogenetic analysis showed that the Italian RCV strains are grouped in European (RCV_E1/GI.3) and Australian (RCV_E2/GI.4) RCV clusters, with an estimated country prevalence of 26%. Based on the proposed genotype classification, considering the nucleotide differences of vp60 higher than 15%, we can hypothesise that two other genotypes, GI.5 and GI.6, might exist within the cluster of non-pathogenic viruses.

Comment on Shah et al. Genetic Characteristics and Phylogeographic Dynamics of Lagoviruses, 1988-2021. Viruses 2023, 15, 815

Shah and colleagues [...].

Identification and Characterisation of a Myxoma Virus Detected in the Italian Hare (Lepus corsicanus)

Myxoma virus (MYXV) is a Leporipoxvirus (genus) belonging to the family Poxviridae; it is characterised by a genome of approximately 161 kb dsDNA encoding for several proteins that play an essential role in both host spectrum determination and immunomodulation. The healthy reservoir of the virus is Sylvilagus spp. At the same time, in wild and domestic European rabbits (Oryctolagus cuniculus), MYXV is the etiologic agent of myxomatosis, a disease with an extremely high mortality rate. In 2014, an interspecies jump of MYXV was reported in Lepus europaeus in the UK. In 2018, myxomatosis induced by a new recombinant strain called MYXV-To was identified during a large outbreak in Iberian hares (Lepus granatensis) in Spain. Here, we describe the case of myxomatosis in another hare species: an adult male Italian hare (Lepus corsicanus) found dead in 2018 in Sicily with lesions suggestive of myxomatosis and treponema infection. Laboratory tests, e.g., end-point PCR and negative staining electron microscopy, confirmed the presence of both pathogens. MYXV was then isolated from tissue samples in permissive cells and sequenced using NGS technology. Main genomic differences concerning known MYXV strains are discussed.