Emergence of a new lagovirus related to Rabbit Haemorrhagic Disease Virus

Abstract

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.

Figure 1

Consensus amino acid sequence alignment of the VP60 gene from RHDV2 and other lagoviruses. The aligned lagovirus sequences correspond to the consensus sequences of i) pathogenic RHDV and RHDVa sequences (47 sequences) belonging to the different genetic groups (G1 to G6) identified by Le Gall-Reculé et al. [16], ii) RCV-A1 sequences (36 sequences). Three other rabbit lagovirus sequences were aligned and correspond to the non-pathogenic RCV (X96868), the non-pathogenic 06–11 (AM268419) and the moderately pathogenic MRCV (GQ166866) strains. Residues differing from the first sequence are shown and a dot corresponds to a deletion. The hypervariable regions V1 to V7 according to Wang et al. [43] are indicated at the top of the alignment. The amino acid S238 (in bold and underlined in the first sequence) corresponds to the beginning of the protrusion domain of the VP60 protein [43]. The RHDV2 mutated amino acids shared by no other rabbit lagovirus are highlighted in grey.

Figure 2

Phylogenetic tree derived for VP60 gene nucleotide sequences of 127 rabbit lagoviruses including 7 RHDV2. The tree was obtained using the Neighbor-Joining method and was drawn to a scale of nucleotide substitutions per site. The percentages greater than 70% of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are given in italics before each major branch node. The European brown hare syndrome virus (EBHSV) strain GD (Z69620) was used as an outgroup to root the tree. The names of some representative strains from different countries are shown. For RHDV, the genetic groups G1 to G6 according to Le Gall-Reculé et al. [16] and clade 1 to 4, or A to D, according to Kerr et al. [18] or to Kinnear et al. [19], respectively, are annotated.

Figure 3

Spatial distribution of RHD outbreaks in wild rabbit populations in France in 2010 and 2011. Data are pooled by département. The color indicates the RHDV strains involved in these outbreaks. Light blue: classic RHDV; dark blue: RHDV2; squared: classic RHDV and RHDV2; white: no data. Red star: first detected outbreak of RHDV2 in a rabbitry (April 2010); white star: first detected case of RHDV2 in a wild population (May 2010).