<P> An RNA virus is a virus that has RNA (ribonucleic acid) as its genetic material . This nucleic acid is usually single - stranded RNA (ssRNA) but may be double - stranded RNA (dsRNA). Notable human diseases caused by RNA viruses include Ebola hemorrhoragic fever, SARS, Rabies, common cold, influenza, hepatitis C, West Nile fever, polio and measles . </P> <P> The International Committee on Taxonomy of Viruses (ICTV) classifies RNA viruses as those that belong to Group III, Group IV or Group V of the Baltimore classification system of classifying viruses and does not consider viruses with DNA intermediates in their life cycle as RNA viruses . Viruses with RNA as their genetic material which also include DNA intermediates in their replication cycle are called retroviruses, and comprise Group VI of the Baltimore classification . Notable human retroviruses include HIV - 1 and HIV - 2, the cause of the disease AIDS . </P> <P> Another term for RNA viruses that explicitly excludes retroviruses is ribovirus . </P> <P> RNA viruses can be further classified according to the sense or polarity of their RNA into negative - sense and positive - sense, or ambisense RNA viruses . Positive - sense viral RNA is similar to mRNA and thus can be immediately translated by the host cell . Negative - sense viral RNA is complementary to mRNA and thus must be converted to positive - sense RNA by an RNA - dependent RNA polymerase before translation . As such, purified RNA of a positive - sense virus can directly cause infection though it may be less infectious than the whole virus particle . Purified RNA of a negative - sense virus is not infectious by itself as it needs to be transcribed into positive - sense RNA; each virion can be transcribed to several positive - sense RNAs . Ambisense RNA viruses resemble negative - sense RNA viruses, except they also translate genes from the positive strand . </P>

Viruses that have rna as their genetic material