Ross River virus

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 debilitating tropical disease known as Ross River fever, previously termed 'epidemic polyarthritis'. The virus is suspected to be enzootic in populations of various native Australian mammals, and has been found on occasion in horses. Taxonomically, Ross River virus belongs to the virus genus Alphavirus, which is part of the family Togaviridae. The alphaviruses are a group of small enveloped single-strand positive-sense RNA viruses. RRV belongs to a subgroup of 'Old World' (Eurasian-African-Australasian) alphaviruses, and is considered closely related to Sagiyama virus. The virions (virus particles) themselves contain their genome in a protein capsid 700 Å in diameter. They are characterised by the presence of two glycoproteins (E1 and E2) embedded as trimeric dimers in a host-derived lipid envelope. Because RRV is transmitted by mosquitos, it is considered an arbovirus, a non-taxonomic term for viruses borne by arthropod vectors. In 1928, an outbreak of acute febrile arthritis was recorded in Narrandera and Hay in New South Wales, Australia. In 1943, several outbreaks of arthralgia and arthritis were described in the Northern Territory, Queensland and the Schouten Islands, off the northern coast of Papua New Guinea. The name epidemic polyarthritis was coined for this disease. In 1956, an epidemic occurred in the Murray Valley which was compared to 'acute viral polyarthritis' caused by Chikungunya virus. The Australian disease seemed to progress in milder fashion. In 1956, serological testing suggested an unknown new species of alphavirus (group A arbovirus) was the likely culprit. In July and August 1956 and 1957, a virus recovered from mosquitoes collected near Tokyo, Japan, and was dubbed Sagiyama virus. This was considered a separate species for a time, but now is considered conspecific with Ross River virus. In 1959, a new alphavirus was identified in mosquito (Ochlerotatus vigilax) samples trapped near Ross River, near Townsville, Queensland, Australia. Further serological testing showed that patients who had suffered 'epidemic polyarthritis' in Queensland had antibodies to the virus. The new virus was named Ross River virus, and the disease Ross River fever. The virus itself was first isolated in 1972 using suckling mice. It was found that RRV isolated from human serum could kill mice. However, the serum containing the virus that was used had come from an Aboriginal boy from Edward River, North Queensland. The child had a fever and a rash but no arthritis making the link between RRV and Ross River fever less than concrete.