Epidemic polyarthritis acquired in Fiji

Ross River virus and Barmah Forest virus infections: a review of history, ecology, and predictive models, with implications for tropical northern Australia

The purpose of the present article is to present a review of the Ross River virus (RRV) and Barmah Forest virus (BFV) literature in relation to potential implications for future disease in tropical northern Australia. Ross River virus infection is the most common and most widespread arboviral disease in Australia, with an average of 4,800 national notifications annually. Of recent concern is the sudden rise in BFV infections; the 2005-2006 summer marked the largest BFV epidemic on record in Australia, with 1,895 notifications. Although not life-threatening, infection with either virus can cause arthritis, myalgia, and fatigue for 6 months or longer, resulting in substantial morbidity and economic impact. The geographic distribution of mosquito species and their seasonal activity is determined in large part by temperature and rainfall. Predictive models can be useful tools in providing early warning systems for epidemics of RRV and BFV infection. Various models have been developed to predict RRV outbreaks, but these appear to be mostly only regionally valid, being dependent on local ecological factors. Difficulties have arisen in developing useful models for the tropical northern parts of Australia, and to date no models have been developed for the Northern Territory. Only one model has been developed for predicting BFV infections using climate and tide variables. It is predicted that the exacerbation of current greenhouse conditions will result in longer periods of high mosquito activity in the tropical regions where RRV and BFV are already common. In addition, the endemic locations may expand further within temperate regions, and epidemics may become more frequent in those areas. Further development of predictive models should benefit public health planning by providing early warning systems of RRV and BFV infection outbreaks in different geographical locations.

Possible genetic determinants in epidemic polyarthritis caused by Ross River virus infection

HLA D locus-related (DR) antigens and Gm phenotypes were determined in 30 patients with epidemic polyarthritis following Ross River virus (RRV) infection and contrasted with those in comparison series of 119 (DR) and 1220 (Gm) normal subjects. HLA DR7 (46.7% cf. 21.0%) and the heterozygous Gm phenotype a+x+b+ (33.3% cf. 15.3%) were significantly increased in the patients, with relative risks of 3.3 and 2.8 respectively. The occurrence of Gm a+x+b+ was independent of DR7, and conferred a relative risk of 4.3 in DR7-negative patients. Differences found in clinical features, specific lymphocyte proliferative responses and antibody titres did not reach significant levels. The association with DR7 was inversely related to age in residents of an area of moderate endemic risk, and to levels of natural cell-mediated immunity (natural killer cell activity). These correlations point to possible mechanisms by which genetic traits might influence the occurrence or consequence of RRV infection.

Epidemic polyarthritis in South Australia 1979-1980

During the past season, a further outbreak of Ross River epidemic polyarthritis occurred in South Australia. Significant differences in the epidemiology occurred, which support the hypothesis that the virus is brought to the area by wild birds.

Incubation time of epidemic polyarthritis

The incubation time of epidemic polyarthritis was estimated in 20 patients with evidence of Ross River virus infection after spending less than three weeks in areas of risk. The smallest estimate consistent with all cases was a range of seven to nine days.