Abstract
Chlamydia psittaci is an avian pathogen capable of spill-over infections to humans. A parrot C. psittaci strain was recently detected in an equine reproductive loss case associated with a subsequent cluster of human C. psittaci infections. In this study, we screened for C. psittaci in cases of equine reproductive loss reported in regional New South Wales, Australia during the 2016 foaling season. C. psittaci specific-PCR screening of foetal and placental tissue samples from cases of equine abortion (n = 161) and foals with compromised health status (n = 38) revealed C. psittaci positivity of 21.1% and 23.7%, respectively. There was a statistically significant geographical clustering of cases ~170 km inland from the mid-coast of NSW (P < 0.001). Genomic analysis and molecular typing of C. psittaci positive samples from this study and the previous Australian equine index case revealed that the equine strains from different studs in regional NSW were clonal, while the phylogenetic analysis revealed that the C. psittaci strains from both Australian equine disease clusters belong to the parrot-associated 6BC clade, again indicative of spill-over of C. psittaci infections from native Australian parrots. The results of this work suggest that C. psittaci may be a more significant agent of equine reproductive loss than thought. A range of studies are now required to evaluate (a) the exact role that C. psittaci plays in equine reproductive loss; (b) the range of potential avian reservoirs and factors influencing infection spill-over; and (c) the risk that these equine infections pose to human health.
Highlights
Chlamydia psittaci, a member of the Chlamydiaceae family, is an obligate intracellular pathogen with a broad host range
C. psittaci equine reproductive loss associated with a subsequent zoonotic event[3, 22, 23], we found that the C. psittaci strain associated with this case belonged to an evolutionary lineage of this pathogen found in parrots, leading to the suggestion that spill-over from Australian parrots was responsible for this equine infection
In a previous study from Germany, C. abortus and C. suis were detected by Quantitative PCR (qPCR) in horse placental samples[19]; when a subset of 20 C. psittaci negative samples from the equine reproductive loss cases in this study was screened for the presence of other Chlamydia spp., no positives were detected[24]
Summary
A member of the Chlamydiaceae family, is an obligate intracellular pathogen with a broad host range. Birds are the major reservoir for this species with nearly 500 hundred avian species known to be susceptible to infection and disease, the latter commonly referred to as psittacosis[1]. While there have been rare reports of human-tohuman transmission of C. psittaci[5, 6], contact with infected birds[7] or substrates contaminated with bird excreta[3, 8, 9] appears to be the major route of exposure and potential transmission. Despite its obligate requirement for a host during the replicative phase of its lifecycle, C. psittaci elementary bodies are known to persist in soil and water following shedding from infected birds[10]
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