Linking patterns of ecological change and emerging infectious disease in the Australasian region

Abstract

The rise in emerging infectious diseases (EIDs) over the last 4 decades is concurrent with dramatic changes in global ecology. The two are likely to be associated, given that zoonoses, particularly those of wildlife origin, make up the majority of these disease. EIDs of animals (and invertebrates and plants) are also reported. The objective of my research is to understand how human and animal EIDs in the Australasian and neighbouring South East Asian and East Asian regions are influenced by ecological change. To achieve these objectives the total reported human and animal EIDs, the diversity and characteristics of hosts of zoonotic EIDs and the relationship between major periods of land-use change and infectious disease emergence have been examined. A case study on Hendra virus emergence in eastern Australia has enabled consideration of these and additional interacting variables, including that of virus, host and climatic factors. Source data regarding EIDs were obtained by systematic review of data bases SCOPUS, CABI and Web of Knowledge. Ancillary data were obtained from the IUCN Red List, vegetation, primary production, land-use, rainfall and temperature, Hendra disease outbreak sites, flying fox camp locations and horse distribution. Historical data on disease, development and environmental change in Australia were also sourced from literature. 104 human, 53 livestock and 23 wildlife EIDs are reported for the Australasian-Asian region,1973-2010. Of the human EIDs, 67% are zoonoses, 63% of these are from wildlife, almost exclusively from wild mammals. Novel zoonoses are reported exclusively from bats. Wild mammal hosts of EIDs are more likely to be associated with human-modified land-uses (OR = 15.02; 95 % CI 5.87 - 38.41), here described as synanthropic. Hosts are also likely to be of low conservation risk (OR = 8.56; 95 % CI 3.04 - 24.08). In a continent-wide study of human and animal EIDs in Australia, the country with the greatest EID literature in the region, land-use change is temporarily and biologically plausibly associated with 22% of the total 90 EIDs reported. Queensland is the most frequent location for these. The current decades of accelerated infectious disease emergence are also examined in an historical context. For Hendra virus, the natural hosts are 4 species of increasingly synanthropic fruit bats for which natural habitat loss has been dramatic, and recent, particularly in the state of Queensland. For the 1994-2010 outbreaks, proximity to roost camps of flying foxes in urban and rural residential areas is an important risk factor, here calculated as the odds of outbreaks in postal areas containing fruit bat camps (OR = 40.5, 95% CI (5.16 - 317.52). All outbreaks have occurred within the nightly feeding range of flying fox camps. Despite the strong seasonality of outbreaks (p = 0.013, 95% CI 0.57-0.98), no climatic or vegetation signatures are evident. Recent, dramatic, anthropogenic ecological change, particularly land-use change, puts pressure on wild species to adapt or perish. It is hypothesised that synanthropic species have become an important new source of pathogens for humans through this process.