Medicine (RMH) - Theses
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ItemA 25-year retrospective study of equine abortion in Australia( 2020)Horses (Equus caballus, a subspecies of Equus ferus) have many roles in Australian society and several equine industries contribute greatly to the Australian economy. A recognised major welfare and economic issue to the equine industry is abortion in mares which may be due to infectious or non-infectious causes. Although equine herpesvirus 1 (EHV-1) is considered as a principal cause of infectious abortion in horses, other infectious agents including Chlamydia psittaci, Coxiella burnetii, Toxoplasma gondii, and Leptospira spp. have also been identified as a cause of abortion. Additionally, some of the abortigenic infectious agents are zoonotic, with implications for both human and animal health. The present study investigated abortigenic pathogens in equine abortion cases in Australia using qPCR and metagenomic deep sequencing methods. Using qPCR the prevalence of EHV- 1, C. psittaci, C. burnetii, Leptospira spp. and T. gondii was determined in 600 aborted equine foetal tissues that were submitted from 1994 to 2019 to the diagnostic laboratories at the University of Melbourne.The overall prevalence of C. psittaci and C. burnetii was 6.5% (39/600, 95% CI: 4.7 – 8.8%) and 4% (21/600, 95% CI: 2.2 – 5.3%) respectively. None of the samples were positive for Leptospira spp. and T. gondii. C. psittaci and C. burnetii positive cases were detected in most years that were represented in this study. The prevalence of C. psittaci in Victoria, New South Wales, and South Australia was 7.6% (30/395, 95% CI: 5.4 – 10.6%) and 3.9% (7/182, 95% CI: 1.9 – 7.7%) and 15.4% (2/13, 95% CI: 4.3 – 42.2%) respectively. The prevalence of C. burnetii in Victoria and New South Wales was 3% (10/395, 95% CI: 1 – 5%) and 6% (11/182, 95% CI: 3 – 11%) respectively. These findings highlight the abortigenic potential of these agents in horses across wide geographical regions in Australia and underscore the importance of strict adherence to personal protection and biosecurity measures when dealing with cases of equine abortion. Genotyping and phylogenetic analysis performed on the archived C. psittaci positive samples, as well as samples from recent cases of equine reproductive loss in Victoria, revealed that the C. psittaci detected in the equine abortion cases clustered with the parrot-associated 6BC clade (Genotype A/ST24). The findings suggest that infection of horses may be due to spill-over from native Australian parrots. DNA from a total of 49 equine aborted foetal tissues and 8 placentas from normal deliveries were sequenced using next-generation sequencing (NGS) technology. Several potential abortigenic pathogens including Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Streptococcus equi subspecies zooepidemicus, Pantoea agglomerans, Acinetobacter lwoffii, Acinetobacter calcoaceticus, and Chlamydia psittaci were identified at a high level of relative abundance in a number of the abortion cases. No novel potential abortigenic pathogens were identified. Although NGS offers enhanced diagnostic capability, the findings suggest that existing diagnostic methods to detect known pathogens may be appropriate for identifying infectious causes of equine abortion in Australia given some of the current NGS limitations. Improvements in NGS technologies are likely to facilitate the use of NGS for diagnostics in the future. Greater awareness of the different pathogens causing equine abortions in Australia may assist diagnostic accuracy, reduce human infections and limit disease spread and further losses.