**Background:** The 2019/20 Australian megafires were unprecedented in scale, burning 12.6 million hectares and severely impacting koala populations. Hundreds of koalas were rescued and rehabilitated, but there was no uniform approach to releasing them—some were returned to burnt habitats, others translocated to unburnt areas. The health consequences of returning rehabilitated koalas to burnt landscapes were unknown. This study aimed to compare health parameters (body condition, chlamydial shedding, blood biochemistry, haematology) among rehabilitated koalas released into burnt habitat, non-rescued resident koalas in burnt habitat, and non-rescued resident koalas in unburnt habitat over 12–16 months post-fire.
**Methods:** The study was conducted in the Snowy Monaro Shire, NSW. Thirty-one koalas rescued from fire grounds (January–March 2020) were rehabilitated; 12 were selected for post-release GPS monitoring (rehabilitated group). Twenty-five non-rescued resident koalas were captured: 9 from burnt habitat (Peak View) and 16 from unburnt habitat (Numeralla, ~4 km from fire ground). Health checks occurred at rescue (rehabilitated only), pre-release (5–9 months post-fire), and recapture (12–16 months post-fire). Body condition was scored 1–5 via scapular palpation. Blood was collected for haematology (PCV, TPP, haemoglobin, erythrocytes, MCV, MCHC, MCH, platelets, leukocytes, neutrophils, lymphocytes, monocytes, eosinophils, basophils, NRBCs) and serum biochemistry (urea, creatinine, AST, ALP, GGT, bilirubin, phosphate, ALT). Ocular and urogenital swabs were tested for Chlamydia pecorum by qPCR. Genetic analysis (whole genome sequencing) was performed on 20 koalas. Statistical analyses used linear mixed models with individual as random effect; pairwise comparisons via emmeans.
**Key Results:** Body condition of rehabilitated koalas improved significantly from rescue (mean 1.3 ± 0.14 out of 5) to pre-release and recapture (p < 0.001), and at recapture all groups had similar body condition (p > 0.05). Chlamydia pecorum shedding was detected in 59% of koalas (31/56), predominantly urogenital; only 3 had ocular shedding (all asymptomatic juveniles). No koalas developed clinical chlamydial disease during the study. Most biochemical and haematological parameters were within published reference ranges. Notable differences: urea was higher in rehabilitated and burnt-resident koalas at pre-release compared to unburnt residents (p = 0.005 and p = 0.016, respectively). AST was higher in rehabilitated koalas at rescue vs. pre-release (p = 0.003). ALT was lower at recapture vs. pre-release in both resident groups (p = 0.008 and p = 0.025). Neutrophils were above reference range in nearly half of burnt residents at pre-release but normal at recapture. Lymphocytes were lower in burnt residents vs. unburnt residents at pre-release (p = 0.011) and recapture (p = 0.05). No significant differences in survival were found except a tentative negative association with log ALT (p < 0.05). Genetic analysis showed minimal population structuring and heterozygosity similar to other koala populations (observed 0.172–0.174).
**Clinical Implications:** This is the first study to demonstrate that rehabilitated koalas released into burnt habitats can achieve and maintain body condition comparable to non-rescued residents in both burnt and unburnt areas within 4–16 months post-fire. The lack of clinical chlamydial disease and normal blood parameters suggest that wildfire and rehabilitation did not exacerbate disease or compromise health in this population. These findings support the practice of returning rehabilitated koalas to burnt habitats when adequate food resources (e.g., epicormic regrowth) are available, reducing the need for translocation and associated risks. However, the study was limited to one region and a relatively small sample; further research is needed to confirm these patterns across other koala populations and fire regimes.