Veterinary Science Collected Works - Theses
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ItemCoxiella burnetii environmental contamination from a large multi-site goat farm and its spatial risk profile( 2022)Coxiella burnetii is a zoonotic bacterial pathogen that can infect multiple animal species. Animals rarely develop clinical disease from infection with C. burnetii. When infection occurs in animals, C. burnetii can be found in relatively high concentrations in the reproductive tract and are released into the environment during parturition. Intensively managed small ruminant farms can play an important role in the epidemiology of C. burnetii due to the potential for abundant release of the bacteria into the environment when large numbers of animals give birth during synchronized kidding/lambing events. Outside the host, C. burnetii can attach itself to dust particles and travel by the wind to places distant from the site of disposition. Human infection, Q fever, manifests itself as clinical disease in about 40% of cases and has the potential to be fatal if not treated. Q fever is endemic in Australia, with 2 cases per 100,000 population notified annually and Q fever seroprevalence in Australia is (at the time of writing) the second highest in the world. However, the knowledge of its spatial transmission from infected sources and validated methods to detect C. burnetii in the environment are limited. This thesis assesses the level of C. burnetii environmental contamination in and around a known infected intensively managed multi-site dairy goat farm in Victoria, Australia. The overarching aim of this work was to improve understanding of the environmental epidemiology of C. burnetii using as a case example the geographic distribution of contamination around a known C. burnetii-positive source. As a first step in addressing this aim, a systematic review (Chapter 3) was conducted to identify the main environmental substrate types, sampling, and testing methods available. Critical appraisal of the available evidence showed that a variety of factors play a role in the ability to detect the organism during field sampling and laboratory testing. Chapter 3 concludes with a framework that can be used by future researchers as a guide for environmental field sampling to detect C. burnetii. Given that the primary mode of transmission of C. burnetii is inhalation, determining the level of bacteria circulating in air is important when considering environmental contamination. In Chapter 4, three air sampling devices were compared and validated in a laboratory-based experiment to determine their ability to detect known concentrations of C. burnetii. This chapter showed that the air samplers performed similar at detecting aerosolized C. burnetii and provided detection and quantitation limits for each sampler with the PCR protocol validated in the study. Chapters 5 and 6 were field sampling studies centred around the dairy goat farm in which coxiellosis was endemic. In Chapter 5, an understanding of the level of environmental contamination in and around the kidding sheds was obtained while standardizing laboratory testing methods for different environmental substrates. Chapter 5 served as an assessment of the feasibility and assisted in the design of the larger-scale geospatial field study presented in Chapter 6. The field study found that C. burnetii soil positivity was higher closer to rivers and creeks. The detected association could be due to either contamination of the environment arising from wildlife preferentially aggregating around waterways or runoff of deposited material on topsoil accumulating in and around waterways. Considering the findings of this thesis and previous work in this field, it is evident that C. burnetii environmental contamination is context specific, depending on many factors including but not limited to the source of bacterial release, surrounding terrain and weather conditions. Overall, the work presented in this dissertation serves as a guiding model for research on C. burnetii geospatial contamination elsewhere.
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ItemAn investigation into the role Toxoplasma gondii may play in the health of the southern brown bandicoot (Isoodon obesulus obesulus) and an assessment of environmental contamination with T. gondii( 2020)The southern brown bandicoot (Isoodon obesulus obesulus), a small, ground-dwelling marsupial, is listed as ‘endangered’ under the Australian Environment Protection and Biodiversity Conservation Act 1999. While many factors contributing to population decline are understood, in particular predation and loss of high-quality, connected habitat, there is a lack of knowledge about other threatening processes, including disease, which has contributed to declines in other small mammal species. Toxoplasma gondii, a protozoan intracellular parasite, excreted into the environment by cats, has been shown to cause clinical disease, including death, in many small and medium sized captive and free-ranging marsupials, including the eastern barred bandicoot (Perameles gunnii). Little is known of its effect on southern brown bandicoot populations. This study aimed to investigate the significance of T. gondii to the health of southern brown bandicoot populations on the northern hinterland of Western Port, Victoria and methods of predicting probability of infection with environmental T. gondii. A series of necropsies was performed on 33 southern brown bandicoots collected opportunistically over a five-year period. The causes of death were identified as motor vehicle trauma (22); predation (4); ejected pouch young (2); drowning (1); pyometra (1); possible toxicity and stomach bloating through lentil ingestion (1) and unknown (2). Real-time qPCR was performed on tissues from 30 cases, all of which were negative for the presence of T. gondii DNA. A range of helminths and ectoparasites were collected and identified, most of which had been previously been reported in this species. However, a metastrongyloid helminth species, found by histopathology in the lungs, is reported for the first time in a southern brown bandicoot. To assess environmental contamination with T. gondii, two sites with different cat densities were compared. Seroprevalence of antibodies to T. gondii (n=24) using the Modified Agglutination Technique was performed on trapped southern brown bandicoots. No evidence of infection with T. gondii was found at either site. Molecular (qPCR) methods were used to measure T. gondii oocyst presence in soil samples (n= 594) and prevalence of T. gondii in tissues of rabbits (n=118) and mice (n=267). All tests were negative across both sites except for the presence of T. gondii in one rabbit (prevalence 0.85%). These results suggest that rabbits and mice may have the potential to be reliable sentinel species and inform conservation management of the probability of infection with T. gondii in small marsupials. The results from this study are consistent with the concept that opportunistic necropsy is a valuable strategy for passive disease and cause of death surveillance in native wildlife. No evidence was found that T. gondii was impacting the health of southern brown bandicoots, however, further longitudinal health surveys are necessary to determine the true prevalence of disease and causes of mortality. Further studies are recommended to confirm the effectiveness of mice and rabbits as potential sentinel species in a range of ecosystems, including those environments which have higher levels of contamination with T. gondii.