Veterinary Science Collected Works - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemCoxiellosis on Commercial Dairy Goat Farms in Australia: Prevalence, Risks Factors, Risk Assessments, and Surveillance( 2022-12)Coxiella burnetii is the causative agent of coxiellosis in animals and Q fever in humans. Multiple animal species can acquire coxiellosis. Being highly infectious and resilient, C. burnetii is a threat to both animals and humans. Clinical signs of coxiellosis rarely occur in animals except for reproductive disorders such as abortion, stillbirths, weak offspring, reduced milk yields and mastitis. Infected domestic small ruminants can excrete C. burnetii from their milk, urine, faeces and birthing products, therefore being a crucial source of human infections. Once excreted outside the host animal, C. burnetii takes its small cell variant (SCV) form, which can withstand high temperatures and disinfectants, and travel long distances as airborne particles. In 2012, the largest Australian farm-related Q fever outbreak was reported in an intensive dairy goat farm in Victoria. This thesis aims to improve the understanding of C. burnetii status among commercial dairy goat farms in Australia and attempt to establish a framework of a program to minimise the possibility of C. burnetii infection among commercial dairy goat farms. This aim was achieved by a series of studies on the prevalence of C. burnetii among commercial dairy goat farms, risk perceptions among commercial dairy goat farmers and an evaluation of different surveillance methods. A cross-sectional study (Chapter 2) was conducted to quantify the prevalence of C. burnetii infections among commercial dairy goat farmers in Australia and identify risk factors associated with farm positivity. The apparent herd prevalence was 10% (95% CI: 4, 22) and the true herd prevalence estimated to be 3% (95% CI: 0, 18). Samples from herds with >900 milking goats were 6.75 (95% CI: 1.65, 27.7) times more likely to return a C. burnetii positive result compared with farms with no less than 900 milking does. Farms with an increased dairy goat density had higher odds of BTM sample positivity, increasing by a factor of 2.53 (95% CI: 1.51, 4.22) for each order of magnitude increase in the number of goats per acre. In the following chapter (Chapter 3), a study was conducted to identify the pattern of C. burnetii Com1 PCR results in bulk tank milk (BTM) samples as well as production factors that may affect testing results. This longitudinal BTM test study found that Com1 PCR tests fluctuate in positivity. C. burnetii DNA concentration in BTM was associated with the season, farm and fat concentration of the BTM sample. These findings are important for informed decisions when making BTM surveillance plans for C. burnetii infection in dairy goat herds. Based on the findings from Chapter 3, risk perceptions of farmers from test-negative farms for C. burnetii introduction into their herds were investigated and comprehensive risk assessments were undertaken (Chapter 4). Participants perceived Q fever as an important risk but their self-efficacy level was ambiguous. Medium overall risk of C. burnetii introduction was reported by four out of seven participating farms. The introduction of infected goats was perceived to be the most important introduction route, followed by transmission on fomites, introduction from neighbouring domestic animals and spillovers from wildlife. An evaluation of different surveillance methods for detecting C. burnetii infections for herds with different starting probabilities of freedom was conducted in Chapter 5. Seven surveillance strategies were constructed from three candidate surveillance system components, and their performance was evaluated quantitatively. The results show that the most efficient combination of surveillance system components depends on a good understanding of initial herd C. burnetii status and the probability of introduction of infection. Collectively, the findings of this thesis identify, at the time of writing, a relatively low C. burnetii prevalence among commercial dairy goat farms in Australia. However, the risk factors for detecting C. burnetii infection on a farm were related to farm size/intensity and the industry is undergoing change in this regard. Overall, this thesis presents many elements of a framework for developing a market assurance program to achieve confidence in C. burnetii freedom and maintain such status