Ross River virus disease (Ross River Fever) is a common and important cause of arthritis in Australia and the South Pacific Islands. The virus was first isolated from mosquitoes trapped along the Ross River at Townsville. The infection is acquired through mosquito-bite. It may be acquired in many parts of Australia, but the highest individual risk of infection occurs in the tropical regions of Western Australia, the Northern Territory and Queensland. Most people infected with Ross River virus do not show clinical signs or symptoms and so these infections go unnoticed. Symptomatic infection occurs most commonly in adults from 20 to 50 years of age.
The incubation period (time between the bite by a mosquito carrying the virus and start of symptoms of infection) is 7-9 days on average but may range between 3 and 21 days. The usual symptoms are joint and muscle pain, fever and in some cases a rash, headache and fatigue. The fever may be mild and go unnoticed. The rash involves the chest, back and limbs. The joints of the legs and hands are most often affected and back pain is also relatively common.
At least half of patients with the disease are well enough to return to work within a month of the onset of symptoms and about one in ten may be still suffering with joint pain after three months. The illness tends to subside over time with occasional relapses of joint pain and fatigue. The good news is that the virus does not cause permanent damage to joints and that eventually the symptoms will stop.
Most cases of infections occur in coastal regions which have salt-marsh habitats with large populations of the mosquitoes that can carry the virus but cases are occasionally reported in inland areas of Australia. In northern and central Queensland, Ross River virus is active throughout the year, in other states, disease presence follows spring and summer rains because carrier mosquitoes are more likely to breed under wet conditions.
Ross River virus infection in humans is largely a biological accident as humans are not preferred host for the virus. Common hosts for the virus are wallabies, kangaroos, possums, wombats and occasionally dogs, horses, cattle, pigs and humans.
The symptoms of the disease are similar to those of the Barmah Forest virus disease. The similarities of between the Ross River virus illness and those of the Barmah Forest virus indicate the need to confirm that the correct diagnosis has been made using laboratory tests.