Review of pathology records for koalas that died in North America (1976–2016; n=204) and Europe (1987–2017; n=77) yielded 222 records that included necropsy and histopathology reports. Mortality in immature koalas (<1.3 years old; n=68) was most often either not reported or undetermined, influenced heavily by early loss of pouch young. For the North American immature koalas with an established cause of death, bone marrow dysplasia (22%), malnutrition (16%), and pneumonia (14%) were the top disorders identified.
The leading cause of mortality in mature koalas (≥1.3 years old; n=154) differed between North America and Europe. The leading cause of mortality in mature koalas in North America was neoplasia (33%), with 67% of the neoplasias being lymphoid in origin. Other notable mortality categories include: 12% musculoskeletal disorders (12%; dominated by degenerative joint disease); respiratory disease (9%); and gastrointestinal disease (8%).
The leading causes of mortality in mature koalas in Europe were infection (22%) and neoplasia (22%). Infection cases were 65% bacterial (most commonly involving the gastrointestinal and respiratory systems), 17.5% fungal, and 17.5% protozoal. Similar to the North American population, the majority (59%) of neoplasias were lymphoid in origin in Europe.
Koala retrovirus (KoRV) infection is a significant health concern for koalas, both in the wild and in human care. Koala retrovirus is thought to be responsible for an innate immunosuppression and neoplastic induction. While several categories of disease listed above are likely related to KoRV infection (specifically lymphoid neoplasia, bone marrow dysplasia, and opportunistic infections), direct evidence of causation is lacking.
This presentation would not have been possible without the participation of the following persons: Dr Karin Lemberger (Vet Diagnostics, Lyon, France), Dr Eva Martinez Nevado (Zoo Aquarium, Madrid, Spain), Dr Sally A. Nofs (Baylor College of Medicine/Houston Zoo, Houston, TX, USA), Dr Kerstin Jurczynski (Zoo Duisburg, Duisburg, Germany), Dr Hanna Vielgrader (Tiergarten Schönbrunn, Vienna, Austria), Dr Klemens Alton (InHisto Praxis für Tierpathologie, Korneuburg, Austria), Dr Rui Bernardino (Jardim Zoologico, Lisbon, Portugal), Dr Geoff Pye (Disney’s Animal Kingdom, Orlando, FL, USA), Dr Endre Sòs (Budapest Zoo, Budapest, Hungary), and Dr Francis Vercammen (Planckendael Zoo, Malines, Belgium).