Evaluation of the usefulness of laboratory diagnostic methods in RHD outbreak

The field outbreak of RHD that occurred late summer 2012 on a small-scale rabbit-rearing operation in Poland and the usefulness of techniques for RHD virus diagnosis are described. During the epizootic, the overall mortality rate of rabbits older than two months was 77%. Eight liver specimens collected from dead unvaccinated rabbits (aged 3-5 months) underwent virological examinations. RHDV specific antigen was detected in two out of eight liver homogenates by haemagglutination (HA) test and ELISA, one of the two being negative in HA assay. However the presence of genetic material of RHD virus was confirmed by RT-PCR and real-time RT-PCR in all liver samples tested. Based on antigen reactivity in ELISA and sequencing of PCR amplicons of the VP60 gene, the RHDVa subtype strain was identified as the cause of infection. The partial genome sequence of a field isolate (STR 2012), comprising the C-terminus of the polymerase gene and the full capsid protein gene, revealed 91% nucleotide homology to reference FRG89 RHDV isolate and 97% to strain Triptis representing the RHDVa variant. Serological evidence of an RHD outbreak in the STR rabbit-rearing operation was confirmed in a serum sample collected from an unvaccinated surviving rabbit. A cross-reactivity examination of RHDV positive serum revealed a decrease in HI titre against the STR 2012 field antigen, and a decrease in the RHDVa control antigen as compared to classic RHDV.