Veterinary Science Collected Works - Theses
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ItemQ fever in intensively managed dairy goats: Transmission dynamics, production losses and control interventions( 2020)Q fever is a zoonotic disease with a significant impact on public health worldwide. It is caused by the highly infectious bacterium Coxiella burnetii. In humans, Q fever typically manifests as a self-limiting febrile syndrome. C. burnetii infection can also lead to chronic disease presentations and be life-threatening for individuals with underlying risk factors. Australia ranks among the countries with the highest Q fever report rates. Livestock species are the main source of infection for humans and dairy goats have been linked to some of the largest Q fever outbreaks recorded in recent times. In Victoria, Australia, a Q fever outbreak linked to a large dairy goat enterprise occurred in 2012 – 2014. This was the largest farm-associated Q fever outbreak recorded in the country. In the context of a steadily growing dairy goat sector, an improved understating of Q fever dynamics and the efficacy of available control strategies in dairy goats is required. This thesis documents a series of studies designed to better understand factors contributing to the spread of Q fever in this herd and the potential efficacy of different control measures. As a first step, we developed a software prototype for reporting herd performance in intensively managed dairy goat herds. This allowed productivity, reproductive performance, health and mortality to be documented, and enabled the performance of Q fever positive and Q fever negative does to be compared. With this system in place, a panel study was conducted to document the prevalence of C. burnetii shedding at the time of kidding. A heterogeneous C. burnetii shedding pattern was found, characterised by the presence of small numbers of ‘super shedder’ does. Further, does identified as ‘super shedders’ had reduced total lactation milk yields compared with C. burnetii negative does. Demographic data gathered using the herd health software prototype and data on Q fever prevalence from our panel study were used to develop a within-herd transmission model of Q fever. The model was used to assess the expected time to eradication by means of vaccination. In addition, the efficacy of segregation of pregnant does and culling of C. burnetii shedders at the time of parturition or abortion was assessed. Vaccination consistently led to disease eradication, although it required this intervention to be sustained for at least 6.5 (95% CrI: 4.1 to 11.3) years. A combination of vaccination with segregation of pregnant does or culling of C. burnetii shedders at parturition or abortion shortened the median time to eradication. The model was adapted to account for heterogenous shedding patterns and used to test the potential efficacy of a test and remove intervention. We found the removal of super shedders does alone would lead to Q fever eradication. However, tests with a high sensitivity for early detection of super shedders are required for this strategy to be effective.