Psittacosis: A Risk During Pregnancy in Horses

An avian zoonosis is infecting equine populations in Australia. The bacteria, which causes abortions in mares, is believed to originate from native parrots. Chlamydia psittaci primarily infects birds, but there are many potential hosts for this zoonosis. Transmission of the avian infection to humans via inhalation is frequently reported, causing flu-like symptoms that often lead to severe respiratory disease and multi-organ failure. Human psittacosis is a significant public health concern. Cattle, goats, sheep, and horses are not spared. Infection in livestock is associated with respiratory, intestinal, or arthritic diseases, as well as a risk of abortion. Until recently, this latter risk factor was not recognized in horses. A new study supplements existing information on the risks to equines, particularly in Australia, by estimating the incidence of psittacosis over the past twenty-five years. To do so, the authors tested 600 samples—collected from material used by veterinarians during abortions in mares in Australia between 1994 and 2019—for the presence of the bacteria using PCR. Results: 6.5% of the samples tested positive, regardless of the year, with prevalence varying by region. C. psittaci has therefore played a significant role in equine reproductive disorders for several decades. Genotyping and phylogenetic analysis showed that the Chlamydia psittaci isolates from abortion cases were grouped within clade 6BC, a classification generally associated with parrots. Australian horses were therefore likely infected by native parrots. These results underscore the importance of implementing measures to protect and perform sterilization on equipment used during abortions in mares.