Taxonomic considerations

ICTV has agreed [9] to add virus species to the categories of genus, subfamily, family, and order in the universal classification of viruses and has endorsed the following definition of virus species: "A virus species is a polythetic class of viruses that constitutes a replicating lineage and occupies a particular ecological niche" [10]. Inherent in the definition of virus species is the requirement that more than one discriminating character should be considered for distinguishing species. There is no official definition for strain, but it is usually considered that strains are viruses belonging to the same species and having stable and heritable biological, serological, and/or molecular differences.

Strain identification could include, but is not restricted to, a particular symptom descriptor, a different host, a different vector, or a significant genetic difference such as a deletion, repetition, or recombination. In the latter, any combination of letters, numbers, or words could be used to characterize the strain.

An isolate can be used to refer to any virus isolated and can be classified as a strain when sufficient information is available. Because an isolate lacks taxonomic status, any geographical identification; any letter, number, or combination thereof; the year of isolation; or any lab code in use can be used (e.g., East african cassava mosaic virus strain from Malawi, isolate MH; EACMV-MW[MH]).