J. Barnwell

Bio: J. Barnwell is an academic researcher. The author has contributed to research in topics: Chlamydia psittaci & Psittacosis. The author has an hindex of 1, co-authored 1 publications receiving 16 citations.

Molecular evidence to suggest pigeon-type Chlamydia psittaci in association with an equine foal loss.

Abstract: Chlamydia psittaci is an important avian pathogen with spillover from infected wild and domesticated birds also posing a risk to human health. We recently reported a case of C. psittaci equine placentitis associated with further spillover to humans. Molecular typing of this case revealed it belonged to the 6BC clade of C. psittaci, a globally distributed highly virulent set of strains, typically linked to infection spillover from parrots. Equine chlamydiosis associated with C. psittaci infection has previously been reported elsewhere in countries where parrots are not endemic, however, raising questions over the identity of infecting C. psittaci strains and the potential infection reservoirs. In this study, we describe the detection and molecular characterization of C. psittaci in a case of equine abortion in southern Queensland. Equine placenta and fresh liver and lung tissue from the necropsied foetus were positive by C. psittaci-specific qPCR. Chlamydia psittaci-specific multilocus sequence typing and ompA genotyping were used to further characterize the detected equine strains and an additional strain obtained from a dove from a different geographic region presenting with psittacosis. Molecular typing of this case revealed that the infecting equine strains were closely related to the C0sittaci detected in dove, all belonging to an evolutionary lineage of C. psittaci strains typically associated with infections of pigeons globally. This finding suggests a broader diversity of C. psittaci strains may be detected in horses and in association with reproductive loss, highlighting the need for an expansion of surveillance studies globally to understand the epidemiology of equine chlamydiosis and the associated zoonotic risk.

Seventy Years of Chlamydia Vaccine Research - Limitations of the Past and Directions for the Future.

Abstract: Chlamydia is a major bacterial pathogen that infects humans, as well as a wide range of animals, including marsupials, birds, cats, pigs, cattle and sheep. Antibiotics are the only treatment currently available, however, with high rates of re-infection, there is mounting pressure to develop Chlamydia vaccines. In this review, we analysed how Chlamydia vaccine trials have developed over the past 70 years and identified where future trials need to be focused. There has been a strong bias towards studies targeting C. muridarum and C. trachomatis within mice and a lack of studies matching chlamydial species to their end target host. Even though a large number of specific antigenic targets have been studied, the results from whole-cell vaccine targets show slightly more promising results overall. There has also been a strong bias towards systemic vaccine delivery systems, despite the finding that mucosal delivery systems have shown more promising outcomes. However, the only successful vaccines with matched chlamydial species/infecting host are based on systemic vaccine delivery methods. We highlight the extensive work done with mouse model trials and indicate that whole cell antigenic targets are capable of inducing an effective response, protecting from disease and reducing shedding rates. However, replication of these results using antigen preparations more conducive to commercial vaccine production has proven difficult. To date, the Major Outer Membrane Protein (MOMP) has emerged as the most suitable substitute for whole cell targets and its delivery as a combined systemic and mucosal vaccine is most effective. Finally, although mouse model trials are useful, differences between hosts and infecting chlamydial strains are preventing vaccine formulations from mouse models to be translated into larger animals or intended hosts.

An epizootic of Chlamydia psittaci equine reproductive loss associated with suspected spillover from native Australian parrots.

Abstract: Chlamydia psittaci is an avian pathogen capable of spill-over infections to humans. A parrot C. psittaci strain was recently detected in an equine reproductive loss case associated with a subsequent cluster of human C. psittaci infections. In this study, we screened for C. psittaci in cases of equine reproductive loss reported in regional New South Wales, Australia during the 2016 foaling season. C. psittaci specific-PCR screening of foetal and placental tissue samples from cases of equine abortion (n = 161) and foals with compromised health status (n = 38) revealed C. psittaci positivity of 21.1% and 23.7%, respectively. There was a statistically significant geographical clustering of cases ~170 km inland from the mid-coast of NSW (P < 0.001). Genomic analysis and molecular typing of C. psittaci positive samples from this study and the previous Australian equine index case revealed that the equine strains from different studs in regional NSW were clonal, while the phylogenetic analysis revealed that the C. psittaci strains from both Australian equine disease clusters belong to the parrot-associated 6BC clade, again indicative of spill-over of C. psittaci infections from native Australian parrots. The results of this work suggest that C. psittaci may be a more significant agent of equine reproductive loss than thought. A range of studies are now required to evaluate (a) the exact role that C. psittaci plays in equine reproductive loss; (b) the range of potential avian reservoirs and factors influencing infection spill-over; and (c) the risk that these equine infections pose to human health.

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.

A comprehensive review on avian chlamydiosis: a neglected zoonotic disease

Abstract: Avian chlamydiosis is one of the important neglected diseases with critical zoonotic potential. Chlamydia psittaci, the causative agent, affects most categories of birds, livestock, companion animals, and humans. It has many obscured characters and epidemiological dimensions, which makes it unique among other bacterial agents. Recent reports on transmission from equine to humans alarmed the public health authorities, and it necessitates the importance of routine screening of this infectious disease. High prevalence of spill-over infection in equines was associated with reproductive losses. Newer avian chlamydial species are being reported in the recent years. It is a potential biological warfare agent and the disease is an occupational hazard mainly to custom officers handling exotic birds. Prevalence of the disease in wild birds, pet birds, and poultry causes economic losses to the poultry industry and the pet bird trade. Interestingly, there are speculations on the ‘legal’ and ‘illegal’ bird trade that may be the global source of some of the most virulent strains of this pathogen. The mortality rate generally ranges from 5 to 40% in untreated cases, but it can sometimes be higher in co-infection. The intracellular lifestyle of this pathogen makes the diagnosis more complicated and there is also lack of accurate diagnostics. Resistance to antibiotics is reported only in some pathogens of the Chlamydiaceae family, but routine screening may assess the actual situation in all pathogens. Due to the diverse nature of the pathogen, the organism necessitates the One Health partnerships to have complete understanding. The present review focuses on the zoonotic aspects of avian chlamydiosis with its new insights into the pathogenesis, transmission, treatment, prevention, and control strategies. The review also briefs on the basic understandings and complex epidemiology of avian chlamydiosis, highlighting the need for research on emerging one health perspectives.

Detection of a range of genetically diverse chlamydiae in Australian domesticated and wild ungulates.

Abstract: Chlamydiae are globally widespread obligate intracellular bacteria, which several species are a well-recognized threat to human and animal health. In Australia, the most successful chlamydial species are the infamous koala pathogen C. pecorum, and C. psittaci, an emerging pathogen associated with zoonotic events. Little is known about infections caused by other chlamydial organisms in Australian livestock or wildlife. Considering that these hosts can be encountered by humans at the animal/human interface, in this study, we investigated genetic diversity of chlamydial organisms infecting Australian domesticated and wild ungulates. A total of 185 samples from 129 domesticated (cattle, horses, sheep, and pigs) and 29 wild (deer) ungulate hosts were screened with C. pecorum and C. psittaci species-specific assays, followed by a screen with pan-Chlamydiales assay. Overall, chlamydial DNA was detected in 120/185 (65%) samples, including all ungulate hosts. Species-specific assays further revealed that C. pecorum and C. psittaci DNA were detected in 27% (50/185) and 6% (11/185) of the samples, respectively, however from domesticated hosts only. A total of 46 "signature" 16S rRNA sequences were successfully resolved by sequencing and were used for phylogenetic analyses. Sequence analyses revealed that genetically diverse novel as well as traditional chlamydial organisms infect an expanded range of ungulate hosts in Australia. Detection of the C. psittaci and C. pecorum in livestock, and novel taxa infecting horses and deer raises questions about the genetic make-up and pathogenic potential of these organisms, but also concerns about risks of spill-over between livestock, humans, and native wildlife.