Naming lagoviruses

The emergence and discovery of new genotypes and strains of Lagovirus has resulted in nomenclature that varies between papers and is still evolving. This can pose problems for those people who read and write about RHDV.

Genotype, serotype, variant or strain?

Genotype refers to the genetic composition of a virus. Serotype refers its antigenic structure based on the ability to react with antibodies. This is important when it comes to immunity and vaccination.

Viruses can mutate so there are genetic changes. Variants are the result. A viral strain is a genetically stable variant of the genotype.

After the discovery of RHDV2, the term ‘variant’ was often used because the virus was believed to be a new strain of RHDV. Genetic studies have shown that it is a different genotype (and serotype) of lagovirus rather than a variant of RHDV1.

Classification of Lagoviruses

Nomenclature of lagoviruses may be based on the position of the strain within the phylogenetic tree or on its antigenic properties. Qualifiers may be added to the name to signify its genotype (e.g. G1-G6) or the continent in which the strain was discovered e.g. RCV-A (Australia), RCV-E (Europe). For example, RHDV-K5 is a Korean strain of RHDV that is particularly lethal and is still deliberately released in Australia and New Zealand to kill wild rabbits.

Proposed unified classification system

As a result of the confusion surrounding nomenclature of lagoviruses, a unified classification system was proposed in 2017 (Le Pendu et al. 2017) in order to standardise the terms that are used. A condensed version of this system, only showing the way RHD viruses are named, is given below:

Family: Calicivirus

Genus: Lagovirus

Species: Lagovirus Europaeus

Genogroup:    GI (RHDV- like viruses)

                           GII (ESBHSV-like viruses)

Genotype:     GI.1 (RHDV)

                           G1.2 (RHDV2)

Variant:          G1.1a

                           G1.1b etc.

Under this system, the two pathogenic genotypes of RHDV are called Lagovirus europaeus GI.1 and Lagovirus europaeus GI.2. and these terms are used by virologists, epidemiologists and other authors of current scientific papers about lagoviruses.

Commonly used names for the pathogenic serotypes: RHD1 and RHD2

From a veterinary clinician’s perspective, lagovirus nomenclature is somewhat esoteric and, clinically, the serotype rather than the strain of RHDV is most important. In general practice, the two pathogenic serotypes are usually called RHDV1 and RHDV2 and the diseases they cause are referred to as RHD1 and RHD2. These terms commonly appear in vaccine datasheets and in laboratory reports and therefore they are used in this article.