Authors: Begg Angela P, Carrick Joan, Chicken Catherine, Blishen Anna, Todhunter Kristen, Eamens Kieran, Jenkins Cheryl
Journal: Veterinary pathology
Summary
Between 2015 and 2019, researchers examined fetoplacental tissue from 46 equine abortion cases and neonatal losses that tested positive for *Chlamydia psittaci*, representing approximately 10% of all abortion investigations during this period; seven were abortions, 26 premature births, and 13 neonatal deaths. Quantitative PCR and immunohistochemistry (IHC) confirmed *C. psittaci* as the primary cause of loss in 83% of cases (38/46), with characteristic lymphohistiocytic inflammation of the placenta, umbilical cord, amnion, and foetal tissues; lesions were most severe at the umbilical vessel insertion and cervical pole, with hepatitis occurring in half the affected cases and pneumonia in 68%. The organism loads were highest in pooled placental tissue, and whilst qPCR and IHC showed good agreement (83% congruence), IHC had a practical detection limit of approximately 200 gene copies, meaning subclinical or early infections may be missed by histopathology alone. For equine practitioners, these findings underscore *C. psittaci* as a significant reproductive pathogen that warrants diagnostic consideration in abortion clusters and neonatal mortality cases; a multi-tissue sampling approach using qPCR, particularly of placental material, is essential for reliable confirmation and should be coupled with histopathology for optimal case characterisation.
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Practical Takeaways
- •When investigating equine abortion, premature birth, or neonatal death, C. psittaci should be included in differential diagnoses and submitted for qPCR testing of placental tissue, as it accounts for a significant proportion of reproductive losses
- •Characteristic placental pathology includes lymphohistiocytic inflammation of the amnion, chorioallantois, and umbilical cord vasculature—recognition of these lesions should prompt specific testing for Chlamydia
- •Placental tissue is the most reliable sample for detecting and quantifying C. psittaci infection in reproductive loss cases; diagnostic protocols should prioritize intact placental submission with qPCR confirmation
Key Findings
- •C. psittaci was the primary cause of reproductive loss in 83% of cases (38/46 equine pregnancies) based on qPCR confirmation and pathological findings
- •Lymphohistiocytic placentitis with vasculitis was present in 36/38 primary infection cases, affecting amnion, umbilical cord, and chorioallantois
- •Pneumonia occurred in 26/38 cases and hepatitis in 19/38 cases with primary C. psittaci infection
- •qPCR and IHC had 83% congruence, with highest bacterial load detected in pooled placental tissues