The ecology of eastern grey kangaroos, Macropus giganteus, and their potential to be a source of human pathogens in Sydney's water supply catchment

A clean water supply is of fundamental importance to human health. In July to September 1998, Cryptosporidium and Giardia were detected at levels of concern within Sydney's raw drinking water supply. Cryptosporidium and Giardia are parasitic protozoa that cause gastrointestinal illness and are commonly transmitted via faecal contamination. Illness is typically short-lived, but infection in immunocompromised hosts can become persistent and mortality can result. During the 1998 contaminated water supply incident, neither the source nor the genotypes of these pathogens were determined. -- Following the commissioning of the Sydney Catchment Authority (SCA) and the prioritisation of research aimed at protecting the quality of Sydney's drinking water, the potential sources of Cryptosporidium and Giardia in the catchment were identified. The primary sources were bypasses from sewage treatment plants in high rainfall periods; livestock with unrestricted access to creeks and rivers, and feral and native animals residing adjacent to the water supply. Of these native animals, eastern grey kangaroos (Macropus giganteus) were found to harbour Cryptosporidium and Giardia at similar frequencies to the other potential sources. Populations within the inner catchment (adjacent to Warragamba Dam) were unmanaged, which highlighted the need to determine the extent to which this species was transmitting these pathogens to the water supply. -- In this study, I aimed to quantify the ecology of eastern grey kangaroos to evaluate the risk of disease transmission from this species to Sydney's potable water supply. The specific aims of this research in relation to eastern grey kangaroos were to: 1) confirm the presence of zoonotic pathogens (e.g. Cryptosporidum and Giardia); 2) quantify the population density of the species and its influence on pathogen load calculation; 3) enumerate faecal deposition by the species in watershed habitats; 4) assess seasonal habitat use and movement patterns and 5) measure changes in the demography of the species. Inferences on the potential for the transmission of these diseases to humans via the potable water supply were drawn from the ecological data collected. The field surveys for this study took place between March 2004 and December 2007. -- Eastern grey kangaroos harboured zoonotic strains of Cryptosporidium and Giardia. Preliminary analysis revealed the presence of both C. parvum and C. hominis (species known to be infective to humans) and faecal samples were positive for human-infective Giardia duodenalis: assemblage A and B. In addition, the analysis of serum revealed that the population of eastern grey kangaroos were host of zoonotic strains of Leptospira and Toxoplasma. A simple risk assessment concluded that the presence of Cryptosporidium and Giardia in eastern grey kangaroos posed the largest risk to humans via their transmission to the potable water supply, whereas Leptospira and Toxoplasma were considered a lower risk due to different modes of transmission of these two diseases. Previous epidemiological studies conducted in 2002, had found that this population harboured only marsupial specific Cryptosporidium strains, making the results derived during the current study potentially very significant. -- The population densities of eastern grey kangaroos in the Wollondilly River region were among the highest reported for this species (101 - 688 kangaroos per square kilometre). Previous risk assessments of waterborne disease transmission used lower density estimates of 200 kangaroos per square kilometre. Therefore, past assessments used density estimates less than half those typically present and kangaroo densities actually parallel the densities of other species that are considered important sources of pathogens, including livestock animals. Furthermore, because drought conditions were prevalent across the entire sampling period, population densities were presumably lower than in more favourable conditions.