Cutaneous and Respiratory Lesions in Bushfire-Affected Koalas

SIMPLE SUMMARY: In the summer of 2019–2020, multiple states of Australia experienced catastrophic bushfires, with koalas being the main wildlife species rescued. Many suffered burns which affected all parts of their body, but particularly their footpads. It can be more difficult to assess the severity of burns in animals than in humans due to the variation in their foot morphology (footpads, hooves, paws), and because fur covers the majority of their body. Here, we describe the clinical and microscopic findings of burns in koalas, following biopsies obtained from animals that were euthanised on welfare grounds after rescue from bushfire. We also describe microscopic findings in the lungs of koalas due to smoke inhalation. These findings will assist veterinarians involved with triaging koalas affected by burns and help predict if they are candidates for rehabilitation or if their prognosis is too poor. ABSTRACT: In the wake of increasingly frequent bushfires emerging as a threat to wildlife worldwide, koalas have notably been the most rescued species in Australia. However, our understanding of burns and their severity in koalas is limited; hence, this study investigated the histopathological features and depth of burns in koala skin, as well as the presence of smoke-induced respiratory tract damage. In four bushfire-affected koalas that had been euthanised on welfare grounds, skin burns in various body regions were scored based on clinical appearance as superficial, partial thickness, or full thickness. Histological sections of affected regions of skin were assessed as Grades I–IV and showed that furred regions on the ear margins and dorsum were histologically more severe, at Grade III, compared with the clinical score. There was a similar finding for footpad burns, which were the most common body region affected. In the respiratory tract, pulmonary oedema and congestion were evident in all koalas. Overall, the results highlight that cutaneous burn lesions on furred and palmar/plantar surfaces can have higher severity based on the burn depth than is clinically apparent. Therefore, there is a need to consider this when developing treatment plans and establishing prognosis for burnt koalas at triage, as well as that a high likelihood of pulmonary oedema exists.