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Infection & disease

Morbidity and Mortality in the Koala (Phascolarctos cinereus)

Backhouse, TC & Bolliger, A 1961, Australian Journal of Zoology, vol. 9, no.1, pp. 24-37.

Of 28 koalas autopsied in 1960, pneumonia was the leading cause of death in this mortality study, which also presented as a comorbidity with trauma. Other significant causes of death were hepatitis, yeast infections of the species Cryptococcus neoformans, leukaemia and anaemia. Ovarian cysts were observed in a number of the koalas, but it was only the cause of death for koalas whose cysts had become infected. Finally, senility-associated diseases such as cardiac failure were seen at a low level.

  The authors of this paper autopsied koalas to determine cause of death and identify any other health conditions. Six koalas had pneumonia, although with varying degrees of severity and presentation, making it the leading cause of death. Three koalas had hepatitis, as evidenced by inflammation and necrosis of liver tissue. Two had blood diseases, one leukaemia and the other anaemia. A further three animals were found to have infections of Cryptococcus neoformans, all of which were female and so had adverse effects on their reproductive tracts. Six out of the ten female koalas autopsied had ovarian lesions or cysts, which were implicated in the deaths of four. Senility was the primary cause of death in only three of the koalas, suggesting that many are not surviving long enough for senility to pose an issue.

  To draw general conclusions about the significant threats facing koala populations, a larger study would need to be undertaken; however, several noteworthy observations were made that contrasted previous research. Cryptococcus neoformans had only been recorded in humans in Australia, with no previous reporting of cases in animals, yet it was found forming advanced lesions in three of the koalas in the study. This observation suggests that Cryptococcus neoformans may be an emerging threat for the koala. Furthermore, of the female koalas studied, most had ovarian cysts or lesions, and a significant portion of these cysts were infected and/or ruptured, contrasting with humans in which ovarian cysts are rarely become infected.

  An understanding of the causes of death of koalas allows for informed action to be taken in their conservation. Small studies such as this serve to identify directions of interest for larger studies, with this study suggesting that the risk of Cryptococcus neoformans infection in koalas is worthy of further investigation.


Summarised by Laura Wait


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