The environmental and ecological determinants of elevated Ross River Virus exposure in koalas residing in urban coastal landscapes

Abstract

Koala populations in many areas of Australia have declined sharply in response to habitat loss, disease and the effects of climate change. Koalas may face further morbidity from endemic mosquito-borne viruses, but the impact of such viruses is currently unknown. Few seroprevalence studies in the wild exist and little is known of the determinants of exposure. Here, we exploited a large, spatially and temporally explicit koala survey to define the intensity of Ross River Virus (RRV) exposure in koalas residing in urban coastal environments in southeast Queensland, Australia. We demonstrate that RRV exposure in koalas is much higher (> 80%) than reported in other sero-surveys and that exposure is uniform across the urban coastal landscape. Uniformity in exposure is related to the presence of the major RRV mosquito vector, Culex annulirostris, and similarities in animal movement, tree use, and age-dependent increases in exposure risk. Elevated exposure ultimately appears to result from the confinement of remaining coastal koala habitat to the edges of permanent wetlands unsuitable for urban development and which produce large numbers of competent mosquito vectors. The results further illustrate that koalas and other RRV-susceptible vertebrates may serve as useful sentinels of human urban exposure in endemic areas.

Prediction of Ross River Virus Incidence Using Mosquito Data in Three Cities of Queensland, Australia

“…The reservoir hosts, a key element in the RRV transmission cycle, were not included in this study due to a lack of host population distribution data in the relevant geographical areas. The population and distribution of the reservoir hosts, such as koalas [45], and their RRV exposure can be valuable in the context of disease prediction. At present, data available for analysing the mosquito-host associations are also limited.…”

Mosquito bloodmeals can be used to determine vertebrate diversity, host preference, and pathogen exposure in humans and wildlife

“…This is of particular relevance for the investigation of complex zoonoses like RRV where potential hosts are myriad or unknown. The PRNT has been adapted for screening RRV antibodies from the small volumes of blood present in mosquito abdomens 21 and can be used for all vertebrates 23,24 . In tandem with DNA barcoding of the vertebrate origin of the bloodmeal, the adapted PRNT can give a measure of vertebrate host exposure to RRV using mosquitoes.…”