Viruses within the Coronaviridae family show variations within their genome sequences, especially within the major structural protein, the Spike (S) glycoprotein gene. Therefore, many different antigenic forms, serotypes, or variant strains of avian coronaviruses (AvCoV) exist worldwide. Only a few of them, the so called protectotypes, cross protect against different serotypes. New serotypes arise by recombination or spontaneous mutations. From time to time, antigenic virus variants appear which differ significantly from known serotypes. The result of this variability is an inconsistent nomenclature and classification of virus strains. Furthermore, there are currently no standard classification methods defined.

Within the framework of the COST Action FA1207 “Towards control of avian coronaviruses: strategies for diagnosis, surveillance, and vaccination” (working groups “Molecular virology” and “Epidemiology”), we aimed at defining and developing a unified and internationally standardized nomenclature and classification of AvCoVs. We recommend the use of “CoV Genus/AvCov/host/country/specimen id/year” to refer to AvCoV strains.