Epidemiologic, Entomologic, and Virologic Factors of the 2014–15 Ross River Virus Outbreak, Queensland, Australia

Abstract

Australia experienced its largest recorded outbreak of Ross River virus (RRV) during the 2014–15 reporting year, comprising >10,000 reported cases. We investigated epidemiologic, entomologic, and virologic factors that potentially contributed to the scale of the outbreak in Queensland, the state with the highest number of notifications (6,371). Spatial analysis of human cases showed that notifications were geographically widespread. In Brisbane, human case notifications and virus detections in mosquitoes occurred across inland and coastal locations. Viral sequence data demonstrated 2 RRV lineages (northeastern genotypes I and II) were circulating, and a new strain containing 3 unique amino acid changes in the envelope 2 protein was identified. Longitudinal mosquito collections demonstrated unusually high relative abundance of Culex annulirostris and Aedes procax mosquitoes, attributable to extensive freshwater larval habitats caused by early and persistent rainfall during the reporting year. Increased prevalence of these mosquitoes probably contributed to the scale of this outbreak.

Spatial and temporal patterns of Ross River virus in South East Queensland, Australia: identification of hot spots at the rural-urban interface

“…annulirostris and Ae. procax in Brisbane following high rainfall (17). Many of the implicated vectors share similar or overlapping habitat types and have broad host-feeding behaviours (25).…”

Epidemic Alphaviruses: Ecology, Emergence and Outbreaks

“…Recently, around 5000 cases of RRV infection were reported yearly in the country, from 1991 to 2001 [329]. From 2000 to 2016, the mean of reported cases was 4541 per year [330], with emphasis on the 2014-2015 season, when 10,074 RRV cases were reported and constituted the highest number of RRV notifications ever recorded [330,331].…”

“…Addressing this issue is definitely challenging, though of utter importance to improve our knowledge about the RRV dynamics and its epidemic potential. Additionally, among climate variables, local rainfall is probably the most important factor that supports RRV spreading in endemic locations, as increased rainfall may increase the abundance and survival of adult vector mosquitoes [328,330]. However, given the high complexity of RRV ecology, it is imperative to analyze these factors at the local level in order to better predict and control RRVD epidemics [328].…”

Spatial and temporal patterns of Ross River virus in South East Queensland, Australia: identification of hot spots at the rural-urban interface

“…Historically considered a rural disease, cases have increasingly been observed in metropolitan areas of Perth, Brisbane, Sydney and Melbourne since the 1990s [11][12][13][14][15][16]. The largest recorded Australian RRV epidemic occurred from late 2014, and continued through 2015, culminating in a record annual total of 9,544 cases in 2015 [1,17]. Sixty-ve percent of these cases (6,193) were from Queensland, with 4,388 reported from the capital, Brisbane -a ve-fold increase compared with the previous 4 years [18].…”

“…RRV is known to have been transmitted across both urban and peri-urban areas of Brisbane since at least the 1990's, although the speci c determinants of outbreaks remain uncertain [28,29]. Studies of two large outbreaks in Brisbane indicated a wide distribution of cases across the city [14,17], although increased risk has also been associated with living in proximity to freshwater bushland and wetland environments [29,32]. We explored the contemporary distribution and epidemiological characteristics of RRV in SEQ between 2001 and 2016.…”