Understanding the epidemiology of Chlamydia psittaci in Thoroughbred mares and their newborn foals
Creators: name: Anstey, Susan
Publisher: name: University of the Sunshine Coast, Queensland
Year: 2022
Subjects: subject: Chlamydia psittaci
subject: equine
subject: foetal loss
subject: Microbiology
subject: FOS: Biological sciences
subject: Veterinary sciences
subject: FOS: Veterinary sciences

description: Chlamydia psittaci (C. psittaci) poses a threat to the Australian Thoroughbred industry with reproductive loss and a zoonotic risk to veterinarians and farm workers. The aim of this work was to reduce pregnancy losses in the Australian Thoroughbred industry by conducting a study on the epidemiology of C. psittaci infection and disease, focussing on two key aspects of this disease: C. psittaci-infected mare and/or foal; and the potential avian reservoirs of C. psittaci infection. Over two consecutive foaling seasons (2019 – 2020), mares and their foals from several studs in the Hunter Valley, NSW were followed to describe infection dynamics of this challenging pathogen in vivo. This thesis evaluated host and environmental risks that could be associated with these infections. Molecular typing methods were used to characterise C. psittaci strains detected in foetal loss cases. Furthermore, typing platforms were compared to provide confidence for future field epidemiological studies. Finally, C. psittaci was assessed in an alternate intensive production industry, the dairy industry, to better understand prevalence and the risk factors associated with chlamydial infections.
description: This study demonstrated that acute C. psittaci foetal loss occurs yearly in both equine C. psittaci endemic as well as non-endemic regions throughout Australia. In a foaling season, chlamydial foetal loss can occur as an acute event(s) on a single or more farms, as well as an outbreak affecting the whole region. Subclinical C. psittaci infections in healthy equines are also common, however the impact on the equine of low-load infections with no clinical signs, remains unknown. Of particular importance is the novel detection of chlamydial infections in healthy foals. Studies should consider chlamydial co-infection in foals presenting with respiratory disease because C. psittaci requires specific diagnostics and therapy.
description: This study found no investigated risk factors for C. psittaci infection related to the pregnant mare. However, modelling from this study with foal infection as the outcome found that foals being born in winter was a significant predictor of C. psittaci infection. Understanding the temporal influence will have downstream implications to improve prevention strategies. Molecular analyses of infecting strains revealed that clonal C. psittaci ST24 strains continue to be readily detected in samples from foetal loss, including placentae, and to a lesser extent in the aborting mares. The same strains are readily detected in psittacine birds, further supporting the spillover of the pathogen from birds to horses. In addition to horses and birds, these strains are commonly found in human zoonotic events. Ongoing molecular characterisation of the foetal loss strains is important to monitor for the emergence of any novel C. psittaci genotypes that may cause another epizootic. This research has provided valuable information to determine the most effective diagnostic and management strategies to improve pregnancy outcome and mitigate a zoonotic event.