Viruses Down Under

Abstract & Commentary

Synopsis: Ross River and Barmah viruses are causes of febrile illness often associated with severe joint symptoms, which may persist for months.

Source: Ross River/Barmah Forest Viruses—Australia (NSW). ProMED.

Warnings were sent to tourists to the new South Wales Far North Coast of Australia because of an outbreak of infections due to Ross River virus and, possibly, Barmah Forest virus. At the time of the warning, 370 cases had been identified in the affected area.

Comment by Stan Deresinski, MD, FACP

Ross River and Barmah Forest viruses are each mosquito-borne alphaviruses.

Almost 5000 cases of Ross River virus infection are reported annually in Australia, with most cases occurring in the northern states and in coastal areas. Infections occur throughout the year, peaking during the wet season from late November to the end of April. This virus is also present in areas of Indonesia, Papua New Guinea, and the Western Pacific islands of New Caledonia, Fiji, American Samoa, the Solomon Islands, and the Cook Islands. It is transmitted by some species of both Culex and Aedes mosquitoes. Mammals in Australia, most likely wallabies and kangaroos, appear to be natural hosts of the virus.

The incubation period is usually 7-14 days. Infection is often asymptomatic. Among those who develop symptoms, the illness is generally mild, with transient fever, but may often be associated with severe and prolonged joint symptoms, an occurrence that has led to the appellation of "epidemic polyarthritis." Joint involvement is usually acute in onset and symmetrical, with ankles, fingers, wrists, knees, and metacarpophalangeal joints most commonly affected.1 Approximately one-half of patients develop a rash, usually maculopapular, primarily involving the limbs and trunk. Myalgia is common and lymphadenopathy may occur. Joint pain and fatigue may persist for months.1,2 Treatment is symptomatic, with nonsteroidal anti-inflammatory agents often providing significant relief.

Infections due to Barmah virus have been identified much less frequently and, as a consequence, the epidemiological and clinical picture is less well described.3 In general, it causes disease similar to that caused by Ross River virus infection, but with less-frequent arthritis and more prominent rash.4 Analysis of 47 laboratory-confirmed cases that occurred in Victoria over the first 5 months of 2002 found that 95% complained of arthralgias, 90% complained of lethargy, and 73% had a maculopapular rash.5


1. Harley D, et al. Ross River virus disease in tropical Queensland: Evolution of rheumatid manifestations in an inception cohort followed for six months. Med J Aust. 2002;177:352-355.

2. Mylonas AD, et al. Natural history of Ross River virus-induced polyarthritis. Med J Aust. 2002;7:356-360.

3. Lindsay MAD, et al. Emergence of Barmah Forest virus in Western Australia. Emerg Infect Dis. 1995;1: 22-26.

4. Flexman JF, et al. A comparison of the diseases caused by Ross River virus and Barmah Forest virus. Med J Aust. 1998;169:159-163.

5. Passmore J, et al. An outbreak of Barmah Forest virus disease in Victoria. Commun Dis Intell. 2002;26: 600-604.

Dr. Derenski is Clinical Professor of Medicine, Stanford; Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center.