Chlamydia psittaci – don’t be embarrassed

Chlamydia psittaci, a gram negative obligate intracellular bacterium, is an avian pathogen that infects birds globally. The organism may undergo successful cross-host transmission to a number of mammalian hosts, resulting in sporadic infection in other species, including sheep, goats, cattle, horses and cats. Infection with C. psittaci has been associated with abortion, pneumonia, polyarthritis and conjunctivitis. In humans, infection with C. psittaci typically results from direct contact with birds (most commonly parrots) or bird excreta and causes a systemic infectious disease, psittacosis, which is characterised by fever, atypical pneumonia, malaise and myalgia. Further, complications of psittacosis may develop in humans, including myocarditis, endocarditis, hepatitis, reactive arthritis and neurological disease [1]. Recently, C. psittaci has emerged as a potential cause of placentitis, abortion or neonatal disease in horses. Further, outbreaks of psittacosis in humans have developed in association with exposure to products of equine abortion [1] or critically-ill equine neonates, reflecting the emergence of a novel source of infection.
Chlamydia psittaci infection in horses
In 2014, a cluster of five human psittacosis cases occurred at a veterinary school in Australia and at a local horse stud. All cases had exposure to grossly abnormal foetal membranes from a mare with placentitis: C. psittaci was subsequently detect from the membranes by PCR [1] and C. psittaci-specific multilocus sequence typing identified an avian-like C. psittaci strain [2]. Subsequently surveillance of equine abortion in New South Wales by the Department of Primary Industries during 2015-2017 has identified over 30 further cases of abortion from which C. psittaci nucleic acid has been detected. Abortion occurs in the last trimester and is often associated with gross changes indicative of placentitis. Histologically, non-suppurative placentitis, foetal pneumonia and non-suppurative hepatitis are typically present. On affected stud farms, C. psittaci-associated abortions can be single or multiple events and may occur over multiple years (J Carrick, personal communication). While serological testing may detect increased serum concentrations of antibodies against C. psittaci in affected mares, increased titres are unpredictable and often short-lived.
In foals, C. psittaci infection has been associated with neonatal acute respiratory distress syndrome (nARDS) and high rates of mortality. Over the 2016-17 foaling season, 13 cases of C. psittaci-associated nARDS were presented to 3 neonatal intensive care units (NICU) in NSW. At the time of presentation to the NICU, foals were 30 minutes to 5 days old. Foals were usually recumbent, inappetent, markedly obtunded and hypothermic. The foals had variable heart rates (40 - 160 bpm) and respiratory rates (4 - 106 brpm). Common abnormalities present in haematological and blood biochemical analyses were leucopenia, hypoglycaemia, hyperlactataemia, azotaemia and increased concentrations of acute phase proteins. Arterial blood gas analysis typically revealed hypoxaemia, hypercapnoea and mixed acidosis. Radiographic examination revealed marked, diffuse interstitial changes to the lungs. Intensive management of all foals was initiated, including administration of parenteral antimicrobial drugs, intravenous fluid therapy, positive inotropes, parenteral nutrition and respiratory support. Most foals demonstrated progressive clinical deterioration despite treatment and died or were subjected to euthanasia within 36 hours of presentation. Only 2 of 13 foals survived to discharge.
Post-mortem examination of non-surviving foals identified diffuse bronchopneumonia, pulmonary congestion and atelectasis in all foals and hepatic congestion and inflammation was also often present. C. psittaci nucleic acid was variably detected from nasal secretions, rectal mucosa, lung tissue and foetal membranes. Six foals were born on farms with a previously history of abortions that were PCR positive for C. psittaci nucleic acid. All foals were negative for EHV-1 infection, and leptospirosis was excluded in all foals that had a post-mortem examination. As an unprecedented event, an outbreak of psittacosis in veterinary staff and students involved in the intensive care of one of the surviving foals occurred, representing a further emerging route for human infection.

These recent experiences in Australia indicate that C. psittaci should be considered as a differential diagnosis for late-term abortion in mares and neonatal foals with signs of severe systemic disease, including nARDS. Further, the emergence of associations between exposure to products of equine abortion and sick equine neonates have important implications for zoonotic disease and prevention and control of psittacosis in these settings. Personnel involved in the reproductive management of foaling/aborting mares and management of critically-ill neonatal foals may be at increased risk of exposure to C. psittaci and development of psittacosis. As such, appropriate use of personal protective equipment should be considered during these high-risk situations. As the equine manifestations of C. psittaci infection represent emerging and poorly understood aspects of this pathogen, it remains uncertain as to whether manifestations of disease will occur in other geographical locations.

References
[1] Chan, J., Doyle, B., Branley, J., Sheppeard, V., Gabor, M., Viney, K., Quinn, H., Janover, O., McCready, M. and Heller, J. (2017) An outbreak of psittacosis at a veterinary school demonstrating a novel source of infection. One Health. 3, 29-33.
[2] Jelocnik, M., Branley, J., Heller, J., Raidal, S., Alderson, S., Galea, F., Gabor, M. and Polkinghorne, A. (2017) Multilocus sequence typing identifies an avian-like Chlamydia psittaci strain involved in equine placentitis and associated with subsequent human psittacosis. Emerg. Microbes Infect. 6, e7.