viroid /vī″roid/ , a small infective segment of nucleic acid, usually ribonucleic acid (RNA). It is not translated and is replicated by host cell enzymes. Viroids include segments that are complementary to introns and may bind to intron RNA. Viroids are responsible for several plant diseases. Although they have not been associated with animal diseases, viroid-like DNA has been found in cancer cells, and some authorities believe that viroids can evolve into infectious animal viruses. See also intron, plasmid, transposon.
