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An Examination of Disease in Captive Australian Koalas ( Phascolarctos cinereus ) and Potential Links to Koala Retrovirus ( KoRV )
| Content Provider | Semantic Scholar |
|---|---|
| Author | Pye, Geoffrey W. Johnson, Rebecca N. Greenwood, Alex D. |
| Copyright Year | 2014 |
| Abstract | Koalas (Phascolarctos cinereus) are known to suffer from a range of neoplastic and immunodeficiency-related disorders but the importance of these conditions to captive koala populations has not previously been thoroughly examined. This study aimed to improve our understanding of disease in captive koalas by conducting a detailed questionnaire survey across most facilities that house koalas in Australia. Responses were received from 16 facilities across five Australian states that resulted in disease information for a total of 264 koalas. The collated data indicated that neoplasia is the major type of diagnosed disease affecting captive koalas, with lymphoma clearly the most common (c. 40%). A variety of other disorders were reported including bone marrow disease (especially leukaemia), cryptococcosis and dermatitis, the latter of which was the only condition reported from all five states. These data suggest a higher incidence of disease in facilities in Queensland and New South Wales, which are predominantly comprised of northern koalas. Mortality records spanning up to 28 years were received from six of the surveyed facilities which indicated that of 303 deceased captive koalas, 32% of deaths were attributable to the diseases mentioned above. It is likely that the prevalence of disease reported here is an underestimate due to the lack of, or inconsistent application of, appropriate diagnostic investigations amongst facilities from all states. Given that previous research suggests that northern koalas are ubiquitously infected with koala retrovirus (KoRV) and that they have higher viraemic loads than their southern counterparts, there may be a link between KoRV and the higher disease expression among northern koalas postulated here. Further research is required to determine if there is a causal link between KoRV and the predominant diseases among captive koalas reported in this study. Gillett, Amber K. 2014. An examination of disease in captive Australian koalas (Phascolarctos cinereus) and potential links to koala retrovirus (KoRV). In The Koala and its Retroviruses: Implications for Sustainability and Survival, ed. Geoffrey W. Pye, Rebecca N. Johnson and Alex D. Greenwood. Technical Reports of the Australian Museum, Online 24: 39–45. Wild koala (Phascolarctos cinereus) populations are found across a broad geographic range in eastern and south-eastern Australia and occur in the states Queensland (QLD), New South Wales (NSW), Australian Capital Territory (ACT), Victoria (VIC) and South Australia (SA) (Martin & Handasyde, 1999). Koalas are generally referred to as either “northern” or “southern”, a description which is largely determined by state borders. Northern koalas are distributed from north QLD to south of the NSW/VIC border and southern koalas are distributed through most of VIC and SA (Carrick, 2013). Variations in appearance between northern and southern koalas are evident and most notably include longer fur length and larger size in southern compared to northern koalas. In many parts of the species range, populations of wild koalas are declining at alarming rates and local extinctions have already occurred across considerable areas. Declines are largely attributed to habitat loss, trauma (road and domestic/wild dog attacks) and disease within populations (principally chlamydiosis). A further potential threat to koalas that is receiving increased scientific attention 40 Technical Reports of the Australian Museum, Online (2014) No. 24 is koala retrovirus (KoRV). Koala retrovirus (KoRV) has become endogenized in koalas and appears to be 100% prevalent in wild (and captive) QLD and NSW koalas and its presence is being increasingly identified amongst wild koalas in the southern states of Australia VIC and SA (ÁvilaArcos et al., 2013). Retroviruses are known to affect many vertebrate species and can lead to immunosuppression and in some cases neoplasia such as leukaemia and lymphoma (Rosenberg, 2011). These conditions are prevalent in wild and captive koalas and there is speculation that KoRV may play a role in inducing neoplastic and immunosuppressive disorders in koalas. While KoRV appears to be widespread in koalas, the circulating viral load may be of greatest importance in understanding the virus’ impacts in koalas. An association appears to be evident between the presence of high circulating levels of KoRV and immunodeficiency and neoplastic disorders in both wild and captive koala populations throughout Australia (Hanger et al., 2000; Tarlinton et al., 2005). Further research is currently being conducted to better understand the role of KoRV and virus load upon infected individuals, and the potential management implications for captive animals. The most recent tally of captive koalas in Australian facilities from the Zoo and Aquarium Association (ZAA) identified 514 northern koalas and 112 southern koalas currently being held across six of Australia’s seven states. All northern animals, except four, are held in QLD, NSW and WA facilities and almost 80% of the southern animals are listed in VIC and SA. Captive populations originated from wild gene pools of both southern and northern koalas but now captive breeding for zoological collections is commonplace throughout Australia. Captive koalas are also routinely moved between Australian zoos and even exported from Australia to international zoological institutions. Occasionally, wild animals are also incorporated (through government-approved species management programs) into established captive colonies within Australia to use as display animals or in captive breeding programs. Wild koalas approved for such placements have often sustained injuries deeming them not fit to return to the wild, are orphaned hand-raised individuals that have not demonstrated wild instincts or are infertile due to Chlamydia-related reproductive disease. In the latter case, certain state governments prohibit the rerelease of infertile koalas to the wild so after chlamydial treatment and ovariohysterectomy, to remove the diseased reproductive tract, these koalas can be placed in a captive management situation for display and education purposes. Across the facilities that house captive koalas there are increasing reports of neoplastic and potential immunodeficiency disorders. Previous investigations of some captive populations have identified as many as 55% of deaths were attributable to lymphoid neoplasia (Hanger, 1999). Lesions appear to be more frequently reported in the northern koalas and include leukaemia, myelodysplasia, tumours (Fig. 1) and immunodeficiency-like syndromes that tend to include generalized dermatitis and/or stomatitis/ oral ulceration (Fig. 2). Anecdotal reports of recognized patterns in the above syndromes from one generation of captive koala to the next have also been observed, with some facilities having seen more than three generations succumb to the same form of neoplastic diseases (leukaemia and lymphoma) at similar ages (M. Panayiotou, pers. comm.). Other conditions such as cryptococcosis are also encountered in captive populations as an opportunistic infection likely related to immunosuppression (Hanger et al., 2003) and overwhelming environmental load of the organism (Krockenberger et al., 2002). To date, very limited information has been available on the prevalence of specific neoplastic and immunodeficiencylike syndromes in captive koalas throughout Australia. The aim of this manuscript was to collate detailed information on the prevalence of specific neoplastic and potential immunosuppressive disorders within these facilities, examine currently employed diagnostic techniques and discuss the potential role of KoRV in the expression of identified diseases. Materials and methods A questionnaire survey was developed to elicit detailed information from relevant captive koala facilities on the type and prevalence of neoplastic and potential immunosuppression-related syndromes in captive koalas. The survey was electronically distributed to veterinary and wildlife network email server lists including the Australian Wildlife Health Network (AWHN), Wildlife Disease Association (WDA) Australasian section and ZAA (Australasian section). As such, the survey should have been received by representatives of all 39 Australian facilities that house captive koalas and are members of the ZAA. The survey was also directly emailed to individual veterinarians, curators and other wildlife facilities known to the author. The audience captured by this approach was in the order of 750 people/facilities (500 AWHN, 158 WDA, 82 ZAA and 10 personal contacts). Questionnaire recipients were asked a series of questions regarding captive koalas at their facility. Firstly, they were asked the total number of captive koalas currently at their facility and if they had acquired wild koalas for display or breeding purposes. Participants were then asked to state the number of koalas affected by leukaemia, myelodysplasia, erythroid dysplasia, chronic dermatitis or other signs of immunosuppression (including chronic ill thrift, recurrent or persistent stomatitis, oral ulceration and severe debilitating chlamydiosis), cryptococcosis, osteochondroma, lymphoma or other neoplasia. For ease of reporting in this manuscript, leukaemia, myelodysplasia and erythroid dysplasia have been categorized as “bone marrow conditions”, dermatitis, stomatitis and signs of immunosuppression are categorized as “AIDS-like conditions”, cryptococcosis remained as “cryptococcosis” and osteochondroma, lymphoma, and other neoplasia are categorized as “tumours”. Finally, participants were asked if they had recognized any of the mentioned syndromes in multiple generations of the same genetic lineage, and what procedure/s they routinely perform when examining an koala ill from an unspecified cause (survey options included blood smear, bone marrow, abdominocentesis or none at all). Once all data regarding the diseas |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://australianmuseum.net.au/uploads/journals/30985/1612_complete.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
