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Infection & disease

Keratitis in free-ranging koalas (Phascolarctos cinereus) on Magnetic Island, Townsville

Hirst, LW, Brown, AS, Kempster R, Hall, J & Woolcock, JB 1992, Journal of Wildlife Diseases, vol. 28, no. 3, pp. 424-427.

Investigation of 70 free-ranging koalas from Magnetic Island, Queensland revealed that unilateral keratitis was present in 12 koalas and bilateral keratitis in a further 10 koalas. No Chlamydia psittaci was detected in any of the animals and disregarding various other medical conditions such as nasal discharge, there appeared to be no indication of ocular chlamydial infection.

  Ocular examination of the captured koalas was conducted using a hand light and slit lamp with any abnormalities recorded photographically. Analysis of serum was then performed from collected blood samples. The appearance of the keratitis (corneal inflammation) in affected animals was uniform with a central scar along the cornea but an unaffected corneal periphery. Crossing of blood vessels into the stromal scar was occasionally visible. Overall, inflammation was not obvious on the cornea. Further inspection revealed eye discharge in 16 koalas and nasal discharge in five. Additionally, 17 eyes involved some discharge but with no apparent keratitis. All animals were found negative for antibodies of Chlamydia psittaci but eight were Pseudomonas pseudomallei antibody positive on serum analysis.

  The current study was conducted in an attempt to describe an endemic eye disease previously reported in koalas on Magnetic Island. Although 33% of captured koalas had some eye abnormalities, none had corneal changes characteristic of chlamydial infection. Furthermore, 16 incidences of keratitis in one of the two eyes were recorded, this being particularly uncommon for Chlamydia psittaci caused conditions. The lack of noted acute corneal abnormalities makes an endemic infective mechanism unlikely, with a possible explanation being a prior infectious epidemic that abruptly diminished or even another disease entirely. As there was no detection of anti-chlamydial antibodies, the primary cause of the corneal changes is not likely due to Chlamydia psittaci. This further suggests an alternative disease cause. The majority of koalas on the island seemed to be surviving in their habitat despite high opacity of both corneas of the eyes. The authors deduced that koalas with impaired vision as well as chlamydial infection may experience reduced survivability due to the disease and not the visual impairment.

  This study has documented a previously undescribed eye disease that has a high frequency in the population of Magnetic Island, and that does not resemble chlamydial disease. Future studies should aim to investigate the cause and pathology of this disease.

 

Summarised by Alexander Murdoch

 

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