Current status and future directions of Chlamydia pecorum research: a scoping review (2010-2025)

Chlamydia pecorum is globally recognised as an important pathogen of both agricultural and conservation concerns, contributing to significant production losses in livestock and debilitating disease in koalas (Phascolarctos cinereus). This scoping review evaluates the current C. pecorum research trends and identifies critical knowledge gaps. A systematic literature search across six major databases yielded 2,099 records. Following screening and eligibility assessment using the PRISMA-ScR framework, supplemented with the Joanna Briggs Institute Manual for Evidence Synthesis: Scoping Reviews, 194 studies were included and categorised into seven thematic areas: diagnostics and surveillance (n = 56), genotyping (n = 32), genomics (n = 14), co-infections (n = 28), vaccines and therapeutics (n = 39), cell biology (n = 14), and literature reviews (n = 11). While the literature is dominated by studies on diagnostics and molecular epidemiology of livestock and koala infections, C. pecorum genomic data remain sparse, with only seven complete genomes available. The significance of C. pecorum infections in non-koala marsupials, wildlife and other domestic animals remains unclear. Similarly, the contributions of bacterial, viral, and protozoal co-pathogens to disease outcomes across hosts are still poorly defined. Functional cell biology studies are similarly underrepresented and rely on a narrow range of livestock and koala strains. Vaccine trials in koalas and sheep, while promising, have shown limited protection, with current formulations failing to achieve sterilising immunity. Overall, this review highlights the substantial progress in diagnostic and surveillance research while emphasising the urgent need for expanded genomic resources, broader isolate biobanks, and integrated, multidisciplinary approaches, to advance our understanding of C. pecorum cell biology, evolution, transmission, and host-pathogen interactions.