[Discovery of viroids and possible relationship with human and veterinary medicine]

The researches of DIENER and co-workers and those of the SEMANCIK'S group, have recently established that some plant diseases, such as potato spindle tuber, citrus exocortis disease and chrysanthemum stunt, are caused by a new class of pathogens, named viroids. These are the smallest known agents (they are smaller than viruses) having a molecular weight of ca 10(5) daltons, and composed of a highly structured RNA, rich in guanine-cytosine base pairs without a capsid. Little is known about the origin, replication model and pathogenic mechanism of viroids and until now only speculations are possible on these subjects. Some properties of the unknown agents of slow virus diseases (scrapie, Kuru, Creutzfeldt-Jakob disease and mink transmissible encephalopathy), suggest that these alterations in the central nervous system are caused by a sort of animal viroid.