Conjunctivitis Associated with Chlamydia pecorum in Three Koalas (Phascolarctos cinereus) in the Mount Lofty Ranges, South Australia

Chlamydiosis is one of the most significant infectious diseases of koalas (Phascolarctos cinereus). High prevalence of infection and disease has been documented in wild populations in Queensland and New South Wales (Polkinghorne et al., 2013). Chlamydia pecorum is the most prevalent species in koala populations; Chlamydia pneumoniae has a lower prevalence and is associated with milder clinical disease. Common clinical manifestations of Chlamydia infection in koalas include keratoconjunctivitis and urogenital inflammation (Griffith et al., 2013).

Koalas were introduced to the Mount Lofty Ranges in the 1960s from Kangaroo Island (Australia and New Zealand Environment and Conservation Council, 1998). This population has experienced a series of genetic bottlenecks, with small populations of koalas from mainland Victoria historically translocated to French Island and subsequently to Kangaroo Island (Martin and Handasyde, 1999). Population densities in the Mount Lofty Ranges have been estimated at 2.4–8.9 koalas per hectare (TSSC, 1999) with these densities likely to increase (Natural Resource Management Ministerial Council, 2009). Chlamydiosis has not previously been reported in koalas in South Australia and some have considered this population Chlamydia-free (Lawrence et al., 1992). In a South Australian government report, PCR and serology detected Chlamydia in six clinically healthy animals in this population in 1996–1997 (Houlden and St. John, 2000). In 2012 three wild koalas from the Mount Lofty Ranges presented with clinical signs consistent with chlamydiosis.

Koala 1, a male from Greenhill (138°41′S, 34°57′W, Fig. 1), approximately 4–7 yr with a condition score of 3 out of 5 (1 = emaciated to 5 = excellent), presented with severe bilateral conjunctivitis. Circulating antibodies to Chlamydia spp. were detected by complement fixation (titer 1∶32). Conjunctival swabs were positive for C. pecorum (Table 1) by quantitative PCR (qPCR; Wan et al., 2011). Another set of swabs were collected for qPCR testing after 10 days of treatment, demonstrating the persistence of a moderate- to high-grade C. pecorum infection. Seven weeks after presentation the animal was diagnosed with oxalate nephrosis and was euthanized; qPCR showed persistent, low-level shedding of C. pecorum at this time (Table 1). Postmortem examination revealed bilateral, moderate, chronic-active neutrophilic and lymphocytic keratitis with corneal neovascularisation consistent with ocular chlamydiosis (Wan et al., 2011). There was mild prostatic cystic glandular dilation with mild hyperplasia and fibrosis; mild chronic nonsuppurative and rarely neutrophilic urethritis; and bilateral renal lesions characterized by segmental tubular ectasia, tubular epithelial degeneration, mild intratubular inflammation, ghosts of crystal rosettes formed by finely radiating spicules, and mild interstitial fibrosis consistent with oxalate nephrosis (Speight et al., 2012). Conjunctivae were not examined histologically. There were no significant gross or microscopic findings in the bladder.

The underlying cause of the chronic-active urethritis was not evident in the sections examined; however, similar lesions have been associated with chlamydiosis in male koalas (Hemsley and Canfield, 1997), and C. pecorum was detected in the cloacal swab from this koala.

Koala 2, a dependent juvenile female from McLaren Vale (138°32′S, 35°13′W, Fig. 1) with a condition score of 2 out of 5, presented with bilateral purulent conjunctivitis and a serous nasal discharge. Treatment commenced at a private veterinary practice and continued at a wildlife park. Conjunctival swabs were qPCR-positive for C. pecorum (Table 1). Conjunctivitis had resolved clinically by the time qPCR results were received. The animal was not suitable for release and was euthanized due to the potential risk to the captive population. Necropsy revealed very mild nonsuppurative, rarely eosinophilic, perivascular to interstitial conjunctivitis of the right eye. There was mild pigmentary incontinence in the superficial dermis of the left lower eyelid, consistent with previous inflammation at the site, but no active inflammation was observed. There were no significant gross or microscopic findings in the urogenital tract or other tissues.

Koala 3, a male from Highbury (138°41′S, 34°51′W, Fig. 1) approximately 20 mo old using head measurement relationships, with a condition score of 2 out of 5, presented with severe bilateral conjunctivitis, a swollen face and neck, and ulcerated oral mucosa. A conjunctival swab was negative by the Chlamydia-specific, solid-phase direct antigen detection test (Clearview test; Unipath, Bedford, Bedfordshire, UK). The urethra and conjunctivae were swabbed for qPCR. The animal deteriorated rapidly and was euthanized. The animal was not available for necropsy. Subsequently, qPCR revealed high levels of C. pecorum (Table 1).

It is unclear whether these three clinical cases reflect a continuing low level of hitherto unreported disease in the Mount Lofty Ranges or whether the incidence of chlamydiosis is increasing in South Australia. There are anecdotal reports of South Australian koalas being found positive for Chlamydia using the Clearview antigen-detection test, reported to have very high specificity in koalas, and six healthy koalas have previously been found positive by PCR (Houlden and St. John, 2000). The relationship of C. pecorum strains in South Australian koalas to those in other states remains to be determined.

There is some evidence that infection with Chlamydia can progress to clinical disease in response to environmental stressors such as overcrowding and poor nutrition (TSSC, 2011). The Mount Lofty population is subject to fragmentation of habitat, motor vehicle injury, predation by dogs, urbanization, limited genetic diversity, and a high incidence of renal disease (Speight et al., 2012). The koala retrovirus has been reported in the Kangaroo Island population in South Australia (Simmons et al., 2012). The presence of retrovirus in the Mount Lofty population is yet to be established but historical links between these populations make its presence likely. Despite these pressures, the incidence of chlamydiosis in South Australian koalas has been apparently low (Polkinghorne et al., 2013). Chlamydia is considered one of the key threatening processes affecting koala populations in Queensland and New South Wales, and it has been suggested that Chlamydia may become an increasingly important disease in Victorian and South Australian populations. Considering the lack of recorded clinical cases, the prevalence of the disease in South Australia is unknown. Further monitoring of both koala abundance and the incidence of Chlamydia in the Mount Lofty Ranges is warranted.

We thank Diana McGregor and Kim Thompson of Fauna Rescue, Kerry Machado of the Australian Marine Wildlife Research and Rescue Organization, and Cleland Wildlife Park for providing care for the koalas in this report. Adelaide Hills Animal Hospital provided initial assessment and treatment of Cases 1 and 3. Ian Hough provided advice on the treatment and management of Case 1. Aaron Machado performed the gross necropsy for Case 1. The McLaren Vale Veterinary Clinic provided initial assessment and treatment of Case 2. We thank Martina Jelocnik and Charles Wan for qPCR testing. Complement fixation was performed by the Elizabeth MacArthur Agricultural Institute. The Clearview ELISA test, hematology, and biochemistries were performed at Gribbles Veterinary Pathology, Glenside, South Australia.