The Impact of Dryland Salinity and Waterlogging On Mosquito-Borne Disease in Western Australia

Abstract

SAB1-O-04 Introduction: Anthropogenic changes in land use and land cover are primary drivers of ecologic disruption, and have the potential to strongly influence human vulnerability to vector-borne diseases, particularly those carried by mosquitoes. One million hectares in the southwest of Western Australia (5.5% of the region) are currently affected by secondary soil salinization (dryland salinity) and waterlogging caused by extensive clearing of native vegetation, and this is predicted to increase to 5.4 million ha (29%) by 2050. This has led to a steady rise in salt concentration in inland aquatic systems, which progressively compromises ecosystem integrity and reduces aquatic biodiversity. Thus, mosquito species with a high salinity tolerance may be favored over endemic freshwater-breeding species as available freshwater habitat and predator populations decrease. Extensive waterlogging may also increase the overall area of available mosquito breeding habitat. One such salinity tolerant species is Ochlerotatus camptorhynchus, a major vector of Ross River virus (RRV) disease in temperate Australia. The relationship between salinity, mosquitoes, and disease distribution are currently being investigated in the heavily salinised Wheatbelt region of Western Australia. Methods: Mosquito collections were undertaken in regions with varying salinity levels between October 2004 and December 2005 to investigate the seasonal dynamics of the mosquito populations present. Associations were tested using correspondence analysis and non-metric multidimensional scaling (NMDS) methods. All blood-fed mosquitoes collected were tested by direct enzyme-linked immunosorbent assay (ELISA) for blood-meal source identification. Serum neutralization assay testing is currently being carried out to determine the prevalence of IgG antibodies to RRV of residents within these regions. These data will be combined using GIS to analyze the overall impact of dryland salinity on mosquito-borne disease risk. Results: Oc. camptorhynchus breeding was significantly associated with salinity affected sites. The primary bloodmeal source was sheep and marsupials, the latter of which are natural vertebrate hosts for RRV. Results of the serosurvey will also be presented. Discussion and Conclusions: Dryland salinity is significantly associated with breeding of the main mosquito vector for RRV in southwestern Australia. Changes in disease risk in rural communities are currently being evaluated by a concurrent seroprevalence survey. This study indicates the potential impact of environmental degradation on arboviral disease ecology in semi-arid environments. The risk of vector-borne disease in this region of Australia is expected to escalate given the predicted increase in dryland salinity over the next 50 years.