Rabbit haemorrhagic disease (RHD) was first recognized in China in 1984. In Europe, the disease appeared in 1986 in Italy, and in the following years RHD was observed in many other European countries, including Poland in 1988. The disease is caused by RHD virus (RHDV), classified as a representative of the Lagovirus genus within the Caliciviridae family. Lagoviruses include the non-pathogenic rabbit calicivirus (RCV) and the European brown hare syndrome virus (EBHSV). There are three basic variants (subtypes) of pathogenic RHD viruses: classic (RHDV) and antigenic subtypes RHDVa and RHDV2 (RHDVb), distinguished on the basis of epidemiological characteristics, infectious properties and antigenic and genetic modifications. Phylogenetic analysis of RHDV revealed the presence of five genogroups (G1-G5) with similar time of isolation, regardless of the place of occurrence. RHDVa strains are genetically more variable than RHDV, and all RHDVa strains belong to genogroup G6. RHDV2 was diagnosed for the first time in 2010 in domestic and wild rabbits in France, and later in the Iberian Peninsula, and it was called RHDVb. Like the previously identified variants of the RHD virus, RHDV2 spreads to other regions of the world, and in 2011-2016 it was diagnosed in many European countries, North America, Africa and Australia. Strains of RHD2 form a separate, uniform phylogenetic group and are more similar to the non-pathogenic rabbit calicivirus than to pathogenic RHDV and RHDVa. Infections with different variants of RHD viruses are a serious epidemiological, diagnostic and immunological problem. Advanced antigenic changes in RHD viruses limit the usefulness of standard RHD vaccines in controlling the disease.
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