Chlamydia spp., Bordetella bronchiseptica, and Phascolarctid Gammaherpesvirus 1 and 2 Infections in Koalas (Phascolarctos cinereus) in South East Queensland, Australia: Detection in Healthy Individuals and Those with Signs of Respiratory or Other Disease.

The decline in koala (Phascolarctos cinereus) populations has been significantly driven by infectious diseases, with chlamydial disease contributing to this trend. Chlamydia pecorum is often codetected with viruses such as phascolarctid gammaherpesvirus 1 and 2 (PhaHV-1 and PhaHV-2). Koalas can also be infected with other bacteria, including Bordetella bronchiseptica, which causes sporadic respiratory disease outbreaks. Respiratory infections and respiratory disease in koalas remain under-investigated. This study reports the detection of C. pecorum, Chlamydia pneumoniae, Chlamydia psittaci, B. bronchiseptica, PhaHV-1, and PhaHV-2 in 102 samples from 49 koalas that presented to veterinary facilities in South East Queensland, Australia from 2018 to 2023. The koalas included seemingly healthy individuals (n=21), koalas with respiratory disease (n=18), and koalas with other diseases (n=10). Overall, C. pecorum was detected in 37% of koalas, C. pneumoniae in 2%, C. psittaci in 0%, B. bronchiseptica in 18%, PhaHV-1 in 41%, and PhaHV-2 in 6%. Coinfections with three agents were common, particularly in koalas with signs of disease. Among the 18 koalas with respiratory disease, one was coinfected with four agents (B. bronchiseptica, C. pecorum, PhaHV-1, and PhaHV-2), and four were coinfected with three agents (B. bronchiseptica, C. pecorum, and PhaHV-1). Additionally, six koalas had coinfections involving two agents: two with C. pecorum and PhaHV-1, two with B. bronchiseptica and PhaHV-1, one with B. bronchiseptica and C. pecorum, and one with PhaHV-1 and PhaHV-2. Analysis of the genetic diversity of infecting chlamydial strains detected in koalas with respiratory and other diseases, based on the full-length ompA gene, identified previously characterized C. pecorum and C. pneumoniae ompA genotypes, as well as a unique C. pecorum ompA genotype. This study highlights the need for incorporating these infectious agents into koala respiratory diagnostics and emphasizes the need for continued research to investigate the complexities of these infections.