Dryland Salinity and the Ecology of Ross River Virus: The Ecological Underpinnings of the Potential for Transmission

Abstract

Alterations in transmission of vector-borne zoonoses are often linked to environmental change. However, ecological processes that determine variability in potential for transmission are generally not well understood. Ross River virus (RRV, Togoviridae: Alphavirus) is a mosquito-borne zoonosis in Australia with a significant human disease burden. The inland southwest (Wheatbelt) of Western Australia (WA) is substantially affected by an anthropogenic salinization of agricultural land (dryland salinity). Aedes camptorhynchus Thomson (Diptera: Culicidae) is the dominant vector of RRV in southwest WA and is halophilic. As such, dryland salinity may influence potential for RRV transmission by influencing interactions between Ae. camptorhynchus and mammalian hosts. We surveyed areas of the Wheatbelt with varying salinity impacts and found Ae. camptorhynchus was more abundant in saline areas, whereas sheep Ovis aries (Linnaeus 1758, Bovidae) declined with increasing salinity. We used a deterministic model to examine interactions between Ae. camptorhynchus and mammals, and we assessed potential for RRV transmission. We found variation in potential for RRV transmission was positively related to increasing salinity and abundance of Ae. camptorhynchus and negatively associated with increasing abundance of Macropus fuliginosus (Desmarest 1817, Macropodidae). Abundance of Ae. camptorhynchus determined more variation in potential for RRV transmission than other variables. Accordingly, dryland salinity increases the zoonotic potential for RRV transmission primarily by facilitating abundance of Ae. camptorhynchus. Human RRV notifications do not currently reflect the salinity-RRV transmission potential in the Wheatbelt but appear to be associated with RRV activity in the enzootic coastal zone. We speculate dryland salinity is a determinant of potential for RRV transmission but not activity. Dryland salinity is predicted to expand two- to four-fold by 2050. Preservation and restoration of freshwater ecosystems may ameliorate the potential for transmission of RRV and possibly incidence of human disease.

A model for the dynamics of Ross River Virus in the Australian environment

“…We have chosen parameters β mk = β km = 1/2, γ k = 1/6 and b k = .000822, since these are estimated from data obtained in the field (Carver, Spafford, Storey, & Weinstein, 2009;Mayberry, Maloney, Mawson, & Bencini, 2010). is unstable for small b m , as discussed in (7), and is therefore denoted with a dashed line in Figure 2(a).…”

Prioritising wetlands subject to secondary salinisation for ongoing management using aquatic invertebrate assemblages: a case study from the Wheatbelt Region of Western Australia

“…Other social costs relate to the increased incidence of disease. For example, the Ross River virus (RRV) mosquito vector Aedes camptorhynchus (Thomson, 1868) was found to be more abundant in saline areas of the Wheatbelt, and importantly, the potential for transmission of RRV, a debilitating human viral infection, was positively correlated with both increasing salinity and abundance of A. camptorhynchus (Carver et al 2009). It was concluded that the preservation and/or restoration of freshwater Wheatbelt habitats may reduce the potential for transmission of the RRV disease (Carver et al 2009).…”

“…For example, the Ross River virus (RRV) mosquito vector Aedes camptorhynchus (Thomson, 1868) was found to be more abundant in saline areas of the Wheatbelt, and importantly, the potential for transmission of RRV, a debilitating human viral infection, was positively correlated with both increasing salinity and abundance of A. camptorhynchus (Carver et al 2009). It was concluded that the preservation and/or restoration of freshwater Wheatbelt habitats may reduce the potential for transmission of the RRV disease (Carver et al 2009). Secondary salinisation also has implications for the ecology of wetlands, including reducing diversity of aquatic invertebrates (Pinder et al 2005), changing aquatic invertebrate assemblage composition , and altering habitat such as the loss of aquatic and fringing vegetation (Froend 1987).…”

Dryland salinity and vector-borne disease emergence in southwestern Australia

“…Transmission of the mosquito-borne disease Ross River virus (RRV) has been noted as a potential adverse human health outcome in salinity-affected regions because the principal vector, Aedes camptorhynchus, is salt tolerant and thrives preferentially in such systems (Carver et al 2009c;Jardine et al 2008a, b;Lindsay et al 2007). RRV disease develops in at least 20% of infected individuals and is characterised by rheumatic joint manifestations, rash, constitutional effects and other presentations including splenomegaly, haematuria, glomerulonephritis, paraesthesia, headache, neck stiffness and photophobia.…”