An RNA virus is a virus that has RNA as its genetic material. Human diseases caused by RNA viruses include Ebola hemorrhoragic fever, SARS, influenza, hepatitis C, West Nile fever, polio, and measles. The 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 but that 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.