CLINICAL SIGNS AND MANIFESTATIONS OF Chlamydiosis in koalas

Although the full range of clinical signs and syndromes caused by chlamydial infection in koalas has not been

comprehensively investigated, the ‘classical’ ocular and urogenital diseases are well described (Blanshard and Bodley 2008).

A rhinitis-pneumonia complex has also been associated with chlamydial infection (Wardrop et al. 1999; Mackie et al. 2016). In some koala populations, high rates of C. pecorum infection are seen in the absence of overt signs of disease, suggesting animals may never have developed Chlamydia-associated disease or have recovered from previous clinical disease.

4.1 Ocular disease

Ocular disease may be unilateral or bilateral (Fig. 35.2). Although different disease classification schemes exist (Wan et al. 2011), ocular chlamydiosis can manifest as an acute active inflammatory conjunctivitis, chronic active conjunctivitis or chronic inactive keratoconjunctivitis. Acute infections are often characterised by serous discharge, blepharospasm and hyperaemia of the conjunctiva and sclera. If left untreated, this progresses to a chronic-active conjunctivitis with purulent discharge, conjunctival hyperplasia, chronic-active neutrophilic and lymphocytic keratitis with corneal neovascularisa- tion and fibrosis. End-stage chlamydial ocular disease manifests as a chronic-inactive keratoconjunctivitis, characterised by extensive conjunctival hyperplasia, minimal erythema and mature scarring without exudation. Blindness may occur because of hyperplastic conjunctiva, chronic keratopathy (oedema, scarring, pannus) and in rare cases, severe ophthalmitis and rupture of the globe (Wan et al. 2011; Funnell et al. 2013; Polkinghorne et al. 2013).

4.2 Urogenital tract disease

Urogenital tract (UGT) disease may affect the kidneys, bladder and urethra in both sexes; upper reproductive tract in females and prostate, epididymis and testes in males (Wan et al.

2011; Marschner et al. 2014; Johnston et al. 2015). Affected animals often present with discoloured and urine-soaked fur around the rump and tail (‘dirty tail’ or ‘wet bottom’), caused by incontinence associated with cystitis and urethritis (Fig. 35.3) (Polk- inghorne et al. 2013; Marschner et al. 2014). UGT disease may manifest as an acute or chronic cystitis. Acute cystitis is characterised by pyuria and mild thickening of the bladder wall. In females, there may be suppurative exudation from the common vestibule without reproductive tract involvement. Chronic cases may progress to inactive cystitis with marked thickening of the bladder wall

Fig. 35.2. Clinical manifestation of chlamydial ocular disease in the koala (Phascolarctos cinereus). (a) Acute active inflammatory conjunctivitis with conjunctival hyperaemia, (b) unilateral chronicactive conjunctivitis with conjunctival hyperplasia and (c) severe, end-stage ocular disease with globe rupture and collapse. Photos: (a) and (b) Australia Zoo Wildlife Hospital, (c) Moggill Wildlife Hospital

Fig. 35.3. Clinical manifestation of urogenital tract chlamydial disease in koalas (Phascolarctos cinereus). (a) 'Wet bottom', characterised by discolouration of the fur around the rump and tail, (b) acute cystitis with rump discolouration and mild urinary incontinence and (c) more severe inflammatory cystitis with urinary incontinence and haematuria. Photos: A Gillett, Australia Zoo Wildlife Hospital

without pyuria in both males and females, and ovarian bursal cysts without major structural changes in the uteri in females. Marked structural changes in the bladder, kidneys and/or reproductive tract, with active cytological inflammation (including pyuria), can also occur. Structural changes in the reproductive tract (detectable ultrasonographically) may be associated with infertility in female koalas (Wan et al.

2011; Marschner et al. 2014) and may be present without overt signs of chlamydiosis (Marschner et al. 2014). Chlamydia pecorum may also cause infertility in male koalas through chronic active granulomatous orchitis and epididymitis with interstitial fibrosis, and degeneration of spermatogenic cells (Johnston et al. 2015; Hulse et al. 2020). In males, C. pecorum DNA could be readily detected in both histologically normal samples as well as samples with inflammation, with the highest incidence in the penile urethra, prostate, membranous urethra, and bulbourethral glands. This suggests that chlamydial infections in the reproductive tract of male koalas is more widespread than originally thought and might be a reservoir for persistent chlamydial infections in koala populations (Palmieri et al. 2019).

4.3 Other chlamydial diseases

A syndrome of rhinitis-pneumonia, most commonly associated with C. pneumoniae infections is seen in koalas. Clinical signs include dyspnoea, followed by a coughing and/or sneezing, leading to serous and often purulent oronasal discharge (Wardrop et al. 1999; Blanshard and Bodley 2008). Chlamydia pecorum was detected via PCR from the pulmonary tissue of a juvenile koala that died from pneumonia (Mackie et al.

2016). Clinical disease in that animal was characterised by coughing, with audible respiratory sounds and copious mucopurulent exudate. Severe opacity of the entire right lung field and more than half of the left lung field was evident radiographically (Mackie et al. 2016). This case is the first evidence that C. pecorum is capable of infecting the bronchiolar epithelium of the koala, though other unpublished case records exist. Arthritis affecting one or more joints has been observed in a small number of wild koalas presenting to wildlife hospitals in Qld; however, the exact aetiology of this disease remains unknown. Recent molecular analysis identified C. pecorum in the tarsal tissue and synovial fluid of a male koala, which was in poor body condition, blind, with a swollen right tarsal joint, a skull tumour, chronic dermatitis and exhibiting clinical signs consistent with cystitis (Burnard et al. 2018). This

finding suggests that in addition to livestock, C. pecorum has the potential to cause arthritis in the koala.

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Source: Vogelnest L., Portas T. (Eds.). Current Therapy in Medicine of Australian Mammals. CSIRO,2025. — 848 p.. 2025

CLINICAL SIGNS AND MANIFESTATIONS OF Chlamydiosis in koalas

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