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WASTING DISEASE IN THE KOALA, PHASCOLARCTOS CINEREUS ROBERT DEGABRIELE* "At Higashiyami Zoo, Nagoya, a koala which died from acute pneumonia was found sitting at the base of his tree, legs wrapped around the trunk. His stomach was full, indicating he was force fed" [I]. This pathetic statement says more about human hysteria and ignorance than it does about koala medicine. The facts are that a koala died from pneumonia and had a full stomach. The inference is that he was force-fed, and one is left wondering about the possible consequences ofthat forced feeding. As one of the Australian biologists who originally advised the government to allow the export of koalas to foreign zoos [2], I feel bound to set the record straight. In the process I also want to demonstrate how irrational and deeply emotional is the perception of the koala by the general public and, I suspect, some biologists. The koala referred to above probably died as a consequence of wasting disease—which is consistent with the reported facts. While the "bug of the month" among koala veterinarians is undoubtedly Chlamidia, which has been implicated in a range of illnesses and deaths, another syndrome that has been mentioned in passing and in an inconclusive way is termed wasting disease. The symptoms of wasting disease include animals becoming emaciated and dying in a coma for no apparent pathological antemortem or postmortem reason [3]. The disease is most prevalent among very young, old, or "weaker" [sic] koalas [4], especially during winter [5] or following a period of drought [6]. Curiously, a full stomach is also observed [3]. The data needed for an explanation of wasting disease exist, yet such an explanation is yet to emerge. I believe there are two possible reasons for this state of affairs. First, the widespread emotional attachment to ?School of Nursing and Health Studies, Macarthur Institute of Higher Education, Campbelltown, N.S.W. 2560, Australia.© 1989 by The University of Chicago. All rights reserved. 0031-5982/89/3203-0635$01 .00 414 I Robert Degabriele ¦ Wasting Disease in the Koala the koala may be hindering rational analysis; the newspaper article containing the statement quoted earlier is but one example of the strength of that attachment. Second, my colleagues have become so specialised in their research focus that they may have lost sight of the big picture. In fact, my hypothesis relies entirely on findings published by others, who might consider themselves to be ecologists, nutritional physiologists, dental morphologists, or veterinarians. I may not have been in a position to formulate the hypothesis myself except for the fact that my current focus on humankind has left me somewhat detached, both scientifically and emotionally, from the koala. What I am proposing, then, is a hypothetical explanation for wasting disease, and I invite my colleagues to test it. The koala is possibly the most specialised arboreal folivore among the Australian marsupials. It feeds almost exclusively on a fibrous, abrasive diet ofEucalyptus leaves throughout life with no obvious dietary changes with age [7]. It has an extremely well-developed hindgut region, especially the proximal colon and caecum, which can be four times body length [8]; this is said to be "the greatest instance of caecal development in the Mammalia" [9]. In addition, the koala selectively retains the solute phase (including fine particles) of the digesta in the caecum and proximal colon, so that mean retention time is 213 hours for the solute phase and 99 hours for the particulate phase [10, 1 1]. Despite these long retention times, total volatile fatty acid production (a measure of microbial fermentation) provides only 9 percent of digestible energy intake, and only 60-70 percent ofthat comes from the digestion ofcell wall [10, 12]. In fact, nonstructural carbohydrate and lipid (i.e., cell contents) are the koala's main source of energy [10, 13]. This means that the efficiency of the teeth in releasing cell contents is critical. The koala's reliance on plant cell contents is reflected in its tooth morphology and mode of occlusion [14]. The molars are selenoid or subselenodont; that is, they have crescent-shaped ridges. They accentuate a shearing action by having high, tightly interlocking cusps with long...


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