Classification
Classification of the RNA viruses has proven to be a difficult problem. This is in part due to the high mutation rates these genomes undergo. Classification is based principally on the type of genome (double stranded, negative or positive single strand) and gene number and organisation. Currently there are 5 orders and 47 families of RNA viruses recognised. There are also a number of unassigned species and genera.
Related to but distinct from the RNA viruses are the viroids and the RNA satellite viruses. These are not currently classified as RNA viruses and are described on their own pages.
Read more about this topic: RNA Virus