Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2021

Chlamydia psittaci: Not a pathogen to horse around with in Australia (#111)

Susan I Anstey 1 , David Lizárraga 1 , Sharon Nyari 1 , Gareth Chalmers 2 , Joan Carrick 3 , Catherine Chicken 4 , Cheryl Jenkins 5 , Nigel Perkins 6 , Peter Timms 1 , Martina Jelocnik 1
  1. Genecology, University of the Sunshine Coast, Sippy Downs, Queensland, Australia
  2. Science and Engineering, University of the Sunshne Coast, Sippy Downs, Qld, Australia
  3. Equine Specialist Consultng, Scone, NSW, Australia
  4. Scone Equine Hospital, Scone, NSW, Australia
  5. NSW Department of Primary industries, Elizabeth Macarthur Agricultural Institute, Menangle, NSW, Australia
  6. Veterinary School, University of Queensland, Gatton, Qld, Australia

Chlamydia psittaci is traditionally regarded as an avian respiratory pathogen with a global distribution that can occasionally cause zoonotic spill over. However, Australia alone has experienced the unique success of a C. psittaci strain that has resulted in late term abortion in pregnant Thoroughbred mares and novel zoonotic transmission from the infected foetal membranes. To better understand this pathogen and success of this strain in Australia, a longitudinal study followed 228 pregnant mares and their newborn foals from 14 stud farms in Australia. We evaluated equine and avian C. psittaci prevalence and investigated potential risk factors, including EHV-1 co-infection and selected climate change events. Molecular epidemiology explored the relationship between host, strain type and disease.

The longitudinal study group recorded no C. psittaci abortion events yet we detected C. psittaci in 13.2% (30/228; CI:0.094-0.182) of healthy newborn foals. Risk factor analysis found that Winter foaling had a significantly higher risk of C. psittaci foal infection than Spring foaling (Adjusted odds ratio = 15.83; P<0.001). A significant correlation was observed between historical abortion cases and frost events (Spearmans’ rho = 0.44; P = 0.002). However, co-infection with EHV-1, being a maiden mare, absence of prophylactic vaginal suture, interventions in the last trimester and residing on a farm with prior history of C. psittaci abortion posed no higher risk to infection in the newborn.

Molecular epidemiology revealed a clonal strain (ST24) dominates Australian mammalian and avian hosts, but strain diversity does exist. A novel strain was detected in an Australian marsupial for the first time.

This study enables strategies to prevent foal loss and potential zoonosis. In Australia, we advise C. psittaci inclusion in an equine abortion diagnostic panel. Finally, this work recommends a revision of the term psittacosis to chlamydiosis to acknowledge the broad host range and provide a more accurate reference for the modern One Health approach.