Identification of Polish RHDVa subtype strains based on the analysis of a highly variable part VP60 gene

In order to determine the genetic variability of Polish RHD virus strains and to confirm the presence of genetic variant (RHDVa) subtype the partial nucleotide sequences of capsid protein gene, including two highly variable regions C and E, were examined. Phylogenetic analyses of 15 viral strains obtained over 18 years revealed the presence of three genetic groups. The oldest RHDV strains exhibit very close amino acid sequence similarity (98-99%) to the German FRG89 reference strain and most of European strains of the same period, as well as Chinese isolate from 1984. The HA-negative strains and isolates with variable reactivity in the HA test belong to the second subgroup and exhibit an intermediate level of variability (about 3%) in the analysed VP60 gene fragment. The most genetically variable strains (6-7%) clustered to RHDVa subtype. The analysis of nucleotides and amino acid sequences demonstrated three pairs of well conserved RHDV strains, isolated over 3, 6 and 10-year period.