Sara Pagliarani, PhD Candidate, Mid-Candidature Review Seminar, “Pathology of Chlamydiosis and characterisation of immune cells in the reproductive tract of koalas”
Sara’s advisors are A/Prof Chiara Palmieri, A/Prof Stephen Johnston, Dr Ken Beagley, Prof Hayden Homer.
Several factors are contributing to the decline of the koala (Phascolarctos cinereus), a wild arboreal herbivorous marsupial, currently experiencing dramatic declines across its free-living populations in Australia (McAlpine et al., 2015). Infection with the obligate intracellular bacteria Chlamydia pecorum is one of the major contributing factors to this decline, causing severe ocular and urogenital tract disease. Acute and/or persistent exposure to the pathogen can result in blindness, cystitis and infertility. Although histological studies have provided insight in the inflammatory processes affecting the female genital tract (Blanshard, W., Bodley, 2008; Hemsley and Canfield, 1997; Obendorf D, Handasyde KA, Lee AK, 1990), describing the cystic lesions of the ovarian bursa as a sequela of previous inflammation and fibrotic reactions, understanding the ovarian function in affected animals has been limited. A major contributor to the poor outcomes for female koalas with ovarian bursal cysts is the fact that many animals are euthanised shortly after diagnosis of chlamydial infection (Vogelnest, L., Woods, R. (Eds.), 2008). As there is currently no grading system for koala ovarian function that correlates histological findings to fertility, it means that it is difficult to accurately determine an individual koala’s prognosis or breeding potential. The same scenario applies to the male where a poor understanding of the pathogenesis of chlamydiosis has made difficult to understand the route of testicular infection as haematogenous or ascending, and whether the presence of Chlamydia infection has any impact on semen quality. While C. pecorum is well known to cause urethritis and prostatitis in the male koala, only recently a chronic-active granulomatous inflammation of the testis and epididymis due to this bacterium been described (Johnston et al., 2015).
Furthermore, our understanding of the koala immune response to infectious diseases is limited, mainly because of a lack of species-specific immune reagents. Thanks to the development of immune reagents and advances in the genomic field, several studies have underlined the ability of the koala in producing a strong and long-lasting humoral and cell-mediated immune response against the Chlamydial antigens (Kollipara et al., 2012; Mathew et al., 2014, 2013; Morris et al., 2014). While little is still known about the immune response to the disease, studies on humans infected by Chlamydia trachomatis have highlighted that cytokines responses at the mucosal surfaces are leading to a strong T-cell response to the infection (Mangar et al., 2016; Morris et al., 2014)
Due to the recent availability of genomic data and reagents, further studies need to be conducted to understand the immune-pathogenesis of chlamydiosis in koalas and the role of macrophages in chronic infection.
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