Coxiella burnetii is the causative agent of the zoonotic disease, Q fever. The disease Q fever is diagnosed globally, however Australia, and in particular Queensland, has the highest rates of notifications in the world.
This study is the first comprehensive investigation of Q fever in Queensland, with a special focus on paediatric infections. At the time of commencement, very limited data were available on the incidence of Q fever in Queensland, the risk factors associated with infection, and the presentation of the disease in children.
Analysis of 6,797 notified Queensland Q fever cases, confirmed the disease to be mainly confined to rural populations, yet there were a noteworthy number of cases reported from urban and non-rural communities. Alarmingly there were 235 notifications from children in Queensland. Globally, Q fever is considered to be under-reported and therefore a seroprevalence study was performed to truly assess the rate of exposure in the Queensland population.
This seroprevalence study highlighted a wider exposure to the organism, with a substantial number of people being exposed from non-rural communities, along with an increased prevalence in children. Further investigations were performed to identify the sources of exposure, especially in “low risk” populations using PCR. This study identified a number of potential sources of infection to humans including domestic pets, flying foxes and dust.
Q fever is an infectious disease presenting with a wide variety of symptoms which may obscure the clinician’s diagnostic approach and treatment. This thesis investigated specific cases of Q fever in both children and adults where there were unusual presentations, including whole families infected, and a serve case in which the patient had complete organ failure. These cases showed the need for greater understanding and awareness of the disease and also demonstrated that indirect transmission of infection from a family member working in a high risk occupation, to other family members may occur.
Prevention of Q fever in the population through vaccination is highly desirable. To ensure adequate vaccine coverage, genotypic characterisation of the Coxiella strains circulating in the population is necessary. This study determined the range of different genotypes detected, and found new, novel genotypes circulating in Queensland, as well as genotypes that were unique to Australia.
Q fever is a vaccine preventable disease in Australia and has had Federal Government funding to protect workers in high risk occupations. Yet the data generated in this thesis highlighted the need for the vaccine strategy to be revised so that children and family, members of at risk workers are included. The current vaccine has many limitations, including that it requires extensive pre-screening procedures to prevent previously exposed subjects from having an adverse reaction upon vaccination. The vaccine can induce a hyper-sensitised reaction in some subjects, eliciting symptoms of Q fever.
As part of this thesis a cell mediated immunity assay was developed to enable vaccine candidates to be screened for previous exposure without having to be re-exposed to the bacteria in the widely applied skin test. This pre-screening tool will allow children to be screened without the potential for an adverse hypersensitive reaction to occur, and should facilitate the wider administration of the vaccine to this younger age group.
In summary, the results presented in this Thesis, address the knowledge gap regarding the epidemiology and clinical impact of Q fever in the Queensland population. It presents evidence of other populations at risk, which may help to formulate an improved vaccination strategy for Queenslanders, and help shape the Public Health approach to the management of this serious disease.