Equine Psittacosis and the Emergence of Chlamydia psittaci as an Equine Abortigenic Pathogen in Southeastern Australia: A Retrospective Data Analysis.

Simple Summary: Infectious diseases that spread from animals to humans pose a risk to both human and animal health. In recent years, the bacteria Chlamydia psittaci has been identified as an important cause of equine reproductive loss in Australia and has also resulted in human disease following contact with infected horses or horse tissue. This is different from the traditional pathway of transmission from birds to humans. Despite the importance of this bacteria to both horse and human health, infections in horses are incompletely understood, and risks to human and horse health remain. These risks may be exacerbated by the incomplete awareness of Chlamydia psittaci among Australian horse owners and others working in the equine industry. This study sought to identify the total number of cases of equine reproductive loss due to Chlamydia psittaci in Australia between 2018 and 2022 and thus contribute data to our growing understanding of Chlamydia psittaci infection in horses. A total of 31 cases were identified. These were geographically restricted to Victoria and New South Wales and were more commonly detected in the winter and spring. The results show that cases of equine reproductive loss due to Chlamydia psittaci remain consistent and ongoing and highlight the need for further studies. Chlamydia psittaci is an important zoonotic pathogen. Although primarily a pathogen of birds, from which infection can spillover into humans and other mammalian hosts, the importance of C. psittaci as a cause of equine reproductive loss and the risk of infection to humans in contact with infected horses are increasingly being recognised in Australia and elsewhere. Despite the risks to both human and equine health, C. psittaci infection in horses is incompletely understood. This study aimed to update and summarise cases of equine psittacosis in Australia in the period 2018–2022, thus addressing a knowledge gap relating to recent cases in this country. These cases were identified from the examination of records held by state and federal veterinary authorities and from a review of published cases. A total of 31 cases were identified. Spatial and temporal trends were identified, with cases being more prevalent in winter and spring and geographically restricted to Victoria and New South Wales. The results show that cases of equine reproductive loss due to C. psittaci are consistent and ongoing and demonstrate the importance of routinely considering C. psittaci in diagnostic investigations. The need for ongoing study to better understand this important zoonotic pathogen is evident. [ABSTRACT FROM AUTHOR]