Ross River Virus Disease Clusters and Spatial Relationship with Mosquito Biting Exposure in Redland Shire, Southern Queensland, Australia

Abstract

The spatial heterogeneity in the risk of Ross River virus (family Togaviridae, genus Alphavirus, RRV) disease, the most common mosquito-borne disease in Australia, was examined in Redland Shire in southern Queensland, Australia. Disease cases, complaints from residents of intense mosquito biting exposure, and human population data were mapped using a geographic information system. Surface maps of RRV disease age-sex standardized morbidity ratios and mosquito biting complaint morbidity ratios were created. To determine whether there was significant spatial variation in disease and complaint patterns, a spatial scan analysis method was used to test whether the number of cases and complaints was distributed according to underlying population at risk. Several noncontiguous areas in proximity to productive saline water habitats of Aedes vigilax (Skuse), a recognized vector of RRV, had higher than expected numbers of RRV disease cases and complaints. Disease rates in human populations in areas which had high numbers of adult Ae. vigilax in carbon dioxide- and octenol-baited light traps were up to 2.9 times those in areas that rarely had high numbers of mosquitoes. It was estimated that targeted control of adult Ae. vigilax in these high-risk areas could potentially reduce the RRV disease incidence by an average of 13.6%. Spatial correlation was found between RRV disease risk and complaints from residents of mosquito biting. Based on historical patterns of RRV transmission throughout Redland Shire and estimated future human population growth in areas with higher than average RRV disease incidence, it was estimated that RRV incidence rates will increase by 8% between 2001 and 2021. The use of arbitrary administrative areas that ranged in size from 4.6 to 318.3 km2 has the potential to mask any small scale heterogeneity in disease patterns. With the availability of georeferenced data sets and high-resolution imagery, it is becoming more feasible to undertake spatial analyses at relatively small scales.

Is There an Association between Dryland Salinity and Ross River Virus Disease in Southwestern Australia?

“…They conducted the analyses over a range of scales and, with the dense population and large numbers of RRV notifications in the region, were able to utilize a maximum resolution of a 0.25 km 2 grid. They demonstrated clearly that ''the use of arbitrary administrative boundaries for spatial analyses has the potential to mask any small-scale heterogeneity in disease patterns'' (Ryan et al, 2006). This is also equally true for the environmental data.…”

“…Despite the large number of cases included in the analysis, the authors recognized that a spatial analysis at the broad LGA scale could only provide a general indication of disease patterns across the state. Ryan et al (2006) conducted a spatial analysis of RRV cases in Redland Shire, a densely populated urban region in coastal southeast Queensland. They conducted the analyses over a range of scales and, with the dense population and large numbers of RRV notifications in the region, were able to utilize a maximum resolution of a 0.25 km 2 grid.…”

Proximity to Mosquito Breeding Habitat and Ross River Virus Risk in the Peel Region of Western Australia

“…One often neglected outcome of such urban expansion is heightened disease risk as human populations encroach closer to natural mosquito breeding habitats. For example, an increased risk of malaria in Africa (Staedke et al 2003, Midega et al 2012 and Asia (Haque et al 2009) has been demonstrated with decreasing distance to mosquito breeding habitats; living in a residence located within 100 meters from one or more tree hole breeding sites was demonstrated to be associated with almost four times greater risk of La Crosse encephalitis infection in eastern Tennessee (Erwin et al 2002); and areas in southeast Queensland with a greater proportion of wetlands and native vegetation and levels of adult mosquito activity have been associated with higher rates of Ross River virus (RRV; Togaviridae: Alphavirus) (Muhar et al 2000, Ryan et al 2006, Hu et al 2010. These studies exemplify the risks associated with living in proximity to sources of vector populations.…”

Ross River virus infection in a traveller returning from northern Australia

“…The incidence of RRV infection oscillates annually, but RRV has spread into urban areas in the past [8]. In southern Queensland, it was estimated that RRV incidence rates will increase by 8% between 2001 and 2021 [9]. In southwest Western Australia, anthropogenic salinization of the Wheatbelt increased the zoonotic potential for RRV transmission by facilitating abundance of halophilic A. camptorhynchus, the principal mosquito vector [10].…”

“…It is thus likely to see more travel-related RRV infections in the future and a notiWcation system in countries where the disease is not endemic should then be discussed. Targeted control of adult A. vigilax in southern Queensland could potentially reduce disease incidence by an average of 13.6% locally [9]. Although there is substantial expenditure for vector control programs each year, the need to examine how to undertake such programs more eYciently still exists [11].…”