In 2010, a variant of the rabbit haemorrhagic disease virus (RHDV) belonging to a new GI.2 genotype was identified in France and rapidly spread worldwide. Due to antigenic difference, new vaccines including G1.2 strains have been developed to confer adequate protection. An increase in the pathogenicity of the circulating strains was recently reported. The objective of this experimental study was to characterise the infection with a highly pathogenic GI.2/RHDV2/b isolate (2017) and assess the efficacy of Filavac VHD K C+V vaccine (Filavie) against this strain. Four and 10-wk-old specific pathogen-free rabbits were inoculated with a recommended dose of vaccine. After 7 d, controls and vaccinated rabbits were challenged and clinically monitored for 14 d. All animals were necropsied and blood, organs and urine were sampled for quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis. In adult groups, regular nasal and rectal swabbing were performed, and faeces were collected after death to monitor RNA shedding. In control groups, the challenge strain induced acute RHD between 31 and 72 h post-inoculation, with a mortality rate of 100% for kits and 89% for adult rabbits. Except for a shorter mean time to death in kits, similar clinical signs and lesions were observed between age groups. The vaccination significantly prevented all mortality, clinical signs, detection of viral RNA in serum and gross lesions in kits and adult rabbits. In adult groups, we also demonstrated that vaccine significantly protected from detectable RNA shedding via naso-conjunctival and rectal routes. Two weeks after challenge, RNA copies were not detected by PCR in the liver, spleen, lungs, kidneys, faeces and urine of vaccinated adult rabbits. The findings for kits were similar, except that very low levels of RNA were present in the liver and spleen of a few rabbits. These data show that immunisation prevented any significant viral multiplication and/or allowed a rapid clearance. We concluded that, despite the quick evolution of GI.2/RHDV2/b strains, the protection conferred by the vaccine remains adequate. In the context of coexistence of both GI.1 and GI.2 genotypes in some countries, with the circulation of multiples recombinant viruses, the vaccination should be based on the association of strains from both genotypes.

To report PCR results and vaccination status of rabbits with rabbit haemorrhagic disease following an investigation into sudden or unexpected death. Materials and MethOds: PCR testing for RHDV2 and RHDV1 was performed on rabbit liver samples at two laboratories. Laboratory A reported results as positive or negative; Laboratory B reported results quantitatively as RNA copies per mg liver, categorised as negative, inconclusive or positive. The vaccination status of rabbits with both histopathological features of rabbit haemorrhagic disease and positive PCR test results were collated. results: PCR results matched histopathological findings in 188 of 195 (96%) cases. Seven individuals showed equivocal results, all of which had histopathological features of RHD but three tested PCRnegative and four results conflicted between laboratories. RHDV2 was the serotype detected in all PCR-positive cases. Histological features of rabbit haemorrhagic disease and PCR test results were positive in 125 rabbits; 51 unvaccinated, 56 in-date with Nobivac Myxo-RHD and 13 vaccinated against RHDV2-although nine of these were vaccinated within 10 days of death. clinical significance: PCR testing complements histopathology in cases of sudden death in rabbits by confirming the diagnosis and identifying virus serotype, but there can be false negatives. Although RHDV2 is currently prevalent in UK pet rabbits, vaccination against both RHDV1 and RHDV2 is recommended. Failures of RHDV2 vaccine are infrequent.

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