Ross River virus (RRV) is a small encapsulated single-strand RNA Alphavirus endemic to Australia, Papua New Guinea and other islands in the South Pacific. It is responsible for a type of mosquito-borne non-lethal but extremely debilitating tropical disease known as Ross River fever, previously termed "epidemic polyarthritis". There is no known cure, and it can last in the system of the host for up to 20 years. The virus is suspected to be enzootic in populations of various native Australian mammals, and has been found on occasion in horses.