Veterinary Biosciences - Theses
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ItemCharacterising the prevalence of Coxiella burnetii in Victorian wildlife( 2018)Coxiella burnetii (C. burnetii) is an intracellular gram-negative bacterium, which is the causative agent of the widespread zoonotic disease Q fever. Q fever infection in humans can cause flu-like symptoms and sometimes develop into chronic Q fever, possibly leading to endocarditis. Animals infected by C. burnetii often show no clinical signs, although some may develop reproductive problems such as stillbirth and abortion in cattle, sheep, and goats. Worldwide, investigations into the prevalence of C. burnetii in wildlife have been conducted, and results indicate that free-ranging animals could be potential reservoirs of this bacterium, although the role of wildlife in C. burnetii transmission is unclear. Australian marsupials, such as kangaroos, wallabies and bandicoots have also been found to be carriers of C. burnetii. Nevertheless, there has not been a study investigating the prevalence of C. burnetii in Victorian wildlife. Immunodetection and molecular detection are commonly used to diagnose infection with C. burnetii. However, with the discovery and study of Coxiella-like bacteria (CLB), many PCR genes targeted in routine molecular detection assays were found to also be present in CLB. Thus, it is not possible to distinguish between C. burnetii and CLB based on assays targeting these genes. Immunogenicity tests are commonly used for detection of antibodies against C. burnetii in wildlife species. ELISA is a preferred test due to its performance, objective interpretation, and capacity in high-throughput screening. There is, however, no validated ELISA test for detection of C. burnetii antibodies across Australian wildlife species. This project therefore aimed to: a) differentiate C. burnetii from CLB; b) study the prevalence of C. burnetii in Victorian wildlife using PCR/qPCR methods; and c) investigate the possibility of developing an ELISA to detect serum antibodies in a wide range of wildlife species. An overall prevalence of 3.4% (95% CI 1.7 - 5.2%) of C. burnetii was detected in 406 Victorian wildlife samples by qPCR, indicating that Victorian wildlife may act as potential reservoirs of C. burnetii. The highest prevalence of C. burnetii was found in eastern grey kangaroos (Macropus giganteus) at 7.9% (95% CI 3.2 - 12.6%). Other wildlife samples were found to be positive for Coxiella, but the species remained undetermined. These samples may represent samples that are positive for CLB. Three out of the four C. burnetii proteins selected (CBU0109, CBU0612, CBU0891, and CBU1910) as antigen candidates for ELISA development were expressed and purified. Immunogenicity tests were applied to three antigen candidates using C. burnetii positive and negative goat serum samples by Western blotting and indirect ELISA. The results revealed that none of the antigen candidates were suitable for ELISA development as all reacted with C. burnetii negative goat sera. Findings from this project address the importance of appropriate molecular methods used for the detection of C. burnetii. Future investigations into C. burnetii in wildlife should aim to perform the tests on a larger population of animals and wider range of species. The cross-reactivity between antigen candidates and C. burnetii negative goat sera indicates the necessity of validation for immunological methods when they are applied to a new species.