Wasting disease in the koala, Phascolarctos Cinereus
Degabriele, R 1989, Perspectives in Biology and Medicine, vol. 32, no. 3, pp. 414-418.
This article provides a hypothesis for wasting disease in koalas. Some symptoms of wasting disease are weight loss and death in a coma with no indication of infection. Wasting disease is most common among very young, old and weak koalas, and particularly during winter or after droughts. In addition, a full stomach is often seen to accompany wasting disease.
Koalas consume Eucalyptus leaves which are broken down and selectively retained in the digestive tract. Koalas obtain energy mainly from cell contents of Eucalyptus leaves; hence, koalas’ teeth need to efficiently grind down the leaf for the cell contents to be released. When teeth become worn, koalas end up with larger leaf particles in their stomachs. Despite this, older koalas with worn teeth are still able to selectively retain fine particles of leaves in the digestive tracts by eating more and increasing the rate of food movement through the digestive tract. As no new leaves are grown in winter or droughts and existing leaves become tougher to digest, however, koalas may increase their consumption of leaves to allow a sufficient supply of fine particles in the digestive tract. Weak koalas with reduced physiological ability to digest leaves may increase intake of leaves but without an associated increase in the rate of movement of food through the digestive tract. As well, the teeth of very young koalas are not sufficiently developed to masticate tougher leaves. Since young koalas’ teeth will continue to develop surfaces for efficient chewing, young koalas may possibly recover from wasting disease if better leaf becomes available. Weak koalas with efficient dentition may also recover from wasting disease with the provision of more variety and amount of leaves. Old koalas, however, are less likely to recover as their teeth have been worn to a point which prohibits the digestion of tougher leaves. Older koalas may starve during winter and droughts or become malnourished to a point where their immune system is compromised, leading to a secondary cause of death by disease.
An implication of this hypothesis is that with a decrease in species variety in Eucalyptus forests and even in captivity, wasting disease may become more frequent. The author of this article, therefore, proposes for captive environments to have their own diverse Eucalyptus foliage instead of obtaining leaves from surrounding trees to prevent competition for food between captive and wild koalas. In summary, the author of this article suggests that to conserve koalas, their habitats should be conserved first.
Summarised by Millie Thng
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