From traumatic oral fibroma to fatal pneumonia: a multidisciplinary postmortem investigation in a long-term monitored Indo-Pacific bottlenose dolphin (Tursiops aduncus)

BACKGROUND: An Indo-Pacific bottlenose dolphin (Tursiops aduncus) in the coastal waters of Jeju Island, Republic of Korea, exhibited an oral mass and mandibular deformity over a documented 6-year period, including 3 years of intensive longitudinal monitoring by our research team. A multidisciplinary approach combining imaging, pathology, microbiology, and omics analyses was used to assess the dolphin. RESULTS: Post-mortem computed tomography confirmed a mandibular fracture at the oral mass site. Histopathological examination of the oral mass revealed prominent fibroblast proliferation and collagen deposition. Fibropapillomas and desmoid tumors were excluded based on viral detection assays and β-catenin accumulation analysis, supporting a diagnosis of trauma-induced fibroma. Transcriptomic analysis of the tumor tissues identified highly expressed genes associated with extracellular matrix remodeling, myofibroblast activation, and epithelial differentiation, supporting a reactive fibrotic rather than malignant phenotype. Gross necropsy revealed multiple suppurative pulmonary lesions, abundant foamy fluid within the respiratory tract, and diatoms within the pulmonary tissue. Metagenomic sequencing revealed a polymicrobial infection, with Parvimonas micra as the predominant organism. Collectively, these findings are most consistent with aspiration pneumonia, with severe secondary pulmonary infection considered a major contributor to death. In addition, analysis of halogenated organic contaminants revealed accumulation levels consistent with those typically observed in aged individuals, and no evidence was identified indicating a direct causal role in the terminal disease process. CONCLUSIONS: To the best of our knowledge, this is the first study to characterize the pathological features and proposed pathogenic mechanism of traumatic fibroma in a marine mammal, and the first confirmed case of pulmonary abscessation associated with Parvimonas micra infection in this taxonomic group. Overall, these findings provide valuable baseline data for the health monitoring and conservation of marine mammal populations.