Viroid Taxonomy

The International Committee on Virus Taxonomy (ICTV) is the organization responsible for establishing the rules to classify viroids into species, genera, and families, and ultimately to endorse viroid taxonomy. The ICTV recently called for more stringent rules to create new virus and viroid species, which must be based on at least two independent criteria. This chapter discusses the resulting implications and presents an updated viroid classification scheme that takes into account the identification of new viroids by next-generation sequencing and bioinformatics tools, which ICTV may finally accept as new species.