Chimeric VLPs Bearing VP60 from Two Serotypes of Rabbit Haemorrhagic Disease Virus Are Protective against Both Viruses.

The VP60 capsid protein from rabbit haemorrhagic disease virus (RHDV), the causative agent of one of the most economically important disease in rabbits worldwide, forms virus-like particles (VLPs) when expressed using heterologous protein expression systems such as recombinant baculovirus, yeasts, plants or mammalian cell cultures. To prevent RHDV dissemination, it would be beneficial to develop a bivalent vaccine including both RHDV GI.1- and RHDV GI.2-derived VLPs to achieve robust immunisation against both serotypes. In the present work, we developed a strategy of production of a dual-serving RHDV vaccine co-expressing the VP60 proteins from the two RHDV predominant serotypes using CrisBio technology, which uses Tricholusia ni insect pupae as natural bioreactors, which are programmed by recombinant baculovirus vectors. Co-infecting the insect pupae with two baculovirus vectors expressing the RHDV GI.1- and RHDV GI.2-derived VP60 proteins, we obtained chimeric VLPs incorporating both proteins as determined by using serotype-specific monoclonal antibodies. The resulting VLPs showed the typical size and shape of this calicivirus as determined by electron microscopy. Rabbits immunised with the chimeric VLPs were fully protected against a lethal challenge infection with the two RHDV serotypes. This study demonstrates that it is possible to generate a dual cost-effective vaccine against this virus using a single production and purification process, greatly simplifying vaccine manufacturing.

Molecular characterisation of virulence graded field isolates of myxoma virus.

BACKGROUND: Myxoma virus (MV) has been endemic in Europe since shortly after its deliberate release in France in 1952. While the emergence of more resistant hosts and more transmissible and attenuated virus is well documented, there have been relatively few studies focused on the sequence changes incurred by the virus as it has adapted to its new host. In order to identify regions of variability within the MV genome to be used for phylogenetic studies and to try to investigate causes of MV strain attenuation we have molecularly characterised nine strains of MV isolated in Spain between the years 1992 and 1995 from wide ranging geographic locations and which had been previously graded for virulence by experimental infection of rabbits. RESULTS: The findings reported here show the analysis of 16 genomic regions accounting for approximately 10% of the viral genomes. Of the 20 genes analysed 5 (M034L, M069L, M071L, M130R and M135R) were identical in all strains and 1 (M122R) contained only a single point mutation in an individual strain. Four genes (M002L/R, M009L, M036L and M017L) showed insertions or deletions that led to disruption of the ORFs. CONCLUSIONS: The findings presented here provide valuable tools for strain differentiation and phylogenetic studies of MV isolates and some clues as to the reasons for virus attenuation in the field.

Structural and functional analysis of virus factories purified from Rabbit vesivirus-infected Vero cells.

Rabbit vesivirus infection induces membrane modifications and accumulation of vesicular structures in the cytoplasm of infected Vero cells. Crude RaV replication complexes (RCs) have been purified and their structural and functional properties have been characterized. We show that calnexin, an ER-resident protein, RaV non-structural proteins 2AB-, 2C-, 3A-, 3B- and 3CD-like as well as viral RNAs co-localize within membranous structures which are able to replicate the endogenous RNA templates. The purified virus factories protected their viral RNA contents from microccocal nuclease degradation and were inaccessible to exogenously added synthetic transcripts. In addition, we have shown that RCs can be used to investigate uridylylation of native endogenous VPg. In contrast to the observation that the virus factories were inaccessible to RNAs, RCs were accessible to added recombinant VPg which was subsequently nucleotidylylated. Nevertheless no elongation of an RNA chain attached to native or recombinant VPg could be demonstrated.