A cluster of cases of a respiratory illness in staff and students at a rural veterinary school in Australia was traced back to their exposure to the infected fetal membranes from a mare.
A report on the 2014 outbreak has just been published in the journal One Health, highlighting the emergence of an unusual source of psittacosis infection.
Psittacocis is a systemic infectious disease caused by Chlamydia psittaci, which can trigger fever, malaise, muscle pain and atypical pneumonia. Complications can include inflammation and infection around the heart, liver problems, reactive arthritis, and neurological abnormalities.
Birds are the major reservoir, but outbreaks have occurred without direct bird exposure.
In November 2014, health authorities in New South Wales were told of the cluster of respiratory illness at the veterinary school in Wagga Wagga. Inquiries identified another case at a local horse stud.
All cases were traced back to exposure to the equine fetal membranes of the mare in question. Samples of this tissue subsequently tested positive for C. psittaci.
It was determined that nine people were exposed to the infected fetal membranes. Of these, five cases of psittacosis were identified. Two required hospital admission.
Four of the five cases were among staff and students at the veterinary school. The affected staff worked in the veterinary reproduction unit where students were undertaking a rotation at the time.
The identification of the further case in a person at a local equine stud provided a vital lead in determining the source of the infection, with investigators establishing a common exposure to the equine fetal membranes of the mare.
People who had direct contact with the abnormal fetal membranes were more likely to develop disease, the researchers found.
Jocelyn Chan and her colleagues, in their report on the case cluster, said the mare in question was normally kept at a farm in Goulburn, New South Wales. She was transferred to a stud farm in Wagga Wagga three weeks before foaling.
She foaled on November 5, 2014, with two stud staff present. A third stud staff member examined the membranes and stored them in a porous plastic feed bag later in the morning.
The membranes were grossly abnormal, with dark red to black discolouration.
The foal died a week later. The cause of death was not further investigated by stud staff.
The membranes were taken to the university by one of the staff members at the stud, who was also a student at the university. The membranes were examined by two academic staff and three students for teaching purposes.
The next day, a technical staff member from the university transferred the bagged membranes into a watertight bag and stored them in a freezer.
All cases reported fever, fatigue, headache and clinical signs of pneumonia, as identified by doctors.
The onset dates of illness ranged from November 9-17, pointing to an incubation period between 5 and 14 days, and a likely point-source exposure between November 3 and 5, consistent with the exposure to the fetal membrane.
The likely modes of transmission from infected fetal membranes to humans were either via the airborne route or direct inoculation of the eyes or nose.
“The emergence of an association between equine fetal membranes and psittacosis in humans has important implications for disease prevention and control,” the authors said.
The authors noted that, in veterinary medicine, equine fetal membranes were routinely examined for completeness and for signs of disease.
“To prevent infection in at risk groups, the US Compendium of Measures to Control Chlamydophila psittaci Infection recommends the donning of personal protective equipment (PPE) when handling potentially infected birds, and using a biological safety cabinet and other strategies to prevent aerosolisation of infectious particles, when performing necropsies of potentially infected birds.
“We recommend the use of PPE for the examination of abnormal equine fetal membranes to protect veterinarians and other staff involved in the handling of horses.”
They continued: “While previous studies have demonstrated the presence of C. psittaci infection in horses, horses have not previously been considered an important source of infection.”
Further research was required to learn more about its prevalence in horses and other non-avian sources, they added.
The study team comprised Chan, Bridget Doyle, James Branley, Vicky Sheppeard, Melinda Gabor, Kerri Viney, Helen Quinn, Orly Janover, Michael McCready, and Jane Heller, from a range of organisations and institutions.
An outbreak of psittacosis at a veterinary school demonstrating a novel source of infection
Jocelyn Chan, Bridget Doyle, James Branley, Vicky Sheppeard, Melinda Gabor, Kerri Viney, Helen Quinn, Orly Janover, Michael McCready, and Jane Heller.
One Health Volume 3, June 2017, Pages 29–33 https://doi.org/10.1016/j.onehlt.2017.02.003