Chlamydiae from Down Under: The Curious Cases of Chlamydial Infections in Australia

Abstract

In Australia, the most researched and perhaps the most successful chlamydial species are the human pathogen Chlamydia trachomatis, animal pathogens Chlamydia pecorum and Chlamydia psittaci. C. trachomatis remains the leading cause of sexually transmitted infections in Australians and trachoma in Australian Indigenous populations. C. pecorum is globally recognised as the infamous koala and widespread livestock pathogen, whilst the avian C. psittaci is emerging as a horse pathogen posing zoonotic risks to humans. Certainly not innocuous, the human infections with Chlamydia pneumoniae seem to be less prevalent that other human chlamydial pathogens (namely C. trachomatis). Interestingly, the complete host range for C. pecorum and C. psittaci remains unknown, and infections by other chlamydial organisms in Australian domesticated and wildlife animals are understudied. Considering that chlamydial organisms can be encountered by either host at the human/animal interface, I review the most recent findings of chlamydial organisms infecting Australians, domesticated animals and native wildlife. Furthermore, I also provide commentary from leading Australian Chlamydia experts on challenges and future directions in the Chlamydia research field.

Undiagnosed Cases of Human Pneumonia Following Exposure to Chlamydia psittaci from an Infected Rosella Parrot

“…Pets or wild psittacine birds are a major zoonotic reservoir of C. psittaci , with organisms excreted in the faeces and nasal discharge of clinically and sub-clinically infected birds [ 20 ]. As Australia is home to many wild bird species, direct as well as indirect contact with birds is well established and is considered a common risk factor for human psittacosis [ 21 ]. Most humans usually become infected after inhaling C. psittaci which has been aerosolised from dried faeces, feather dust, or respiratory secretions (e.g., sneezed droplets) of infected birds.…”

“…In light of the development of severe respiratory illness in two employees within 10 days after exposure to a clinically ill Adelaide Rosella, confirmed by nucleic acid detection to be infected by C. psittaci , psittacosis is the most probable cause of pneumonia in Employees A and B, despite inconclusive serological testing. Molecular characterisation of the Adelaide Rosella C. psittaci strain resolved ST24/ omp A genotype A type strain, which is commonly found in Australian parrots, horses, humans, and widely associated with zoonotic events and pathogenicity [ 21 ]. In addition to confirmatory laboratory testing of the affected bird, post-mortem observations of emaciation, renomegaly, and hepatomegaly with green discolouration were consistent with avian chlamydiosis.…”

The Koala Immune Response to Chlamydial Infection and Vaccine Development—Advancing Our Immunological Understanding

“…Traditionally identified and studied in birds, cattle, guinea pigs, sheep and humans [ 1 ], continued research has expanded the list of chlamydial hosts to include insects, amphibians, molluscs, arachnids, reptiles, fish, and amoeba, as well as mammals like pigs, goats, deer, cats, bats, possums, and koalas [ 2 ]. Chlamydial disease in the koala, Phascolarctos cinereus , has been particularly well studied, given the devastating toll it has taken on this iconic Australian marsupial ( Figure 1 ) [ 3 , 4 ]. Chlamydial infection in koalas is dominated by the species Chlamydia pecorum .…”

“…Chlamydial infection in koalas is dominated by the species Chlamydia pecorum . These infections lead to ocular and urogenital/reproductive diseases comparable to Chlamydia trachomatis infections in humans, which include keratoconjunctivitis and scarring in the eye leading to blindness and cystitis/nephritis and reproductive cysts in the urogenital and reproductive tracts, respectively, leading to severe pain and infertility [ 3 , 4 ]. In both humans and koalas, vaccination has been identified as the most promising avenue of control for this pathogen [ 5 ].…”

Real-time fluorometric and end-point colorimetric isothermal assays for detection of equine pathogens C. psittaci and equine herpes virus 1: validation, comparison and application at the point of care

“…C. psittaci ( C. psittaci ) has recently emerged as an equine abortigenic pathogen causing significant losses to the Australian Thoroughbred industry [ 3 – 5 ]. Furthermore, this zoonotic pathogen has attracted attention due to the apparent transmission of C. psittaci from equine placental membranes to humans causing severe respiratory illness [ 6 , 7 ]. Equine herpesvirus-1 (EHV-1) also causes equine abortion as well as morbidity and mortalities in neonatal foals.…”