Disseminated and fatal infection by Schizophyllum commune in a harbor seal (Phoca vitulina) kept under human care in Brazil

Abstract

Schizophyllum commune is an environmental basidiomycete increasingly recognized as an opportunistic pathogen in humans and domestic animals, whereas infections in wildlife remain rarely reported. In marine mammals, fungal infections involving the central nervous system and respiratory tract are uncommon and may pose diagnostic challenges. A captive 5-year-old female harbor seal (Phoca vitulina) from Brazil developed progressive neurological abnormalities over approximately 11 months, initially characterized by cervical dystonia and head deviation, followed by respiratory distress, tremors, opisthotonos, hyperthermia, and apnea. Despite supportive treatment, the animal died. Histopathological examination revealed severe pyogranulomatous encephalitis involving the cerebral cortex and severe multifocal to coalescing pyogranulomatous pneumonia, both associated with extensive necrosis and numerous intralesional hyaline, pauciseptate fungal hyphae measuring approximately 2–4 μm in diameter, with irregular branching at angles ranging from 30° to 90°, highlighted by Grocott’s methenamine silver staining. Molecular investigation was performed using panfungal PCR targeting the D1/D2 domain of the 28 S rDNA and the internal transcribed spacer (ITS) region. Sequence analysis, particularly of the ITS region, identified the fungus as S. commune, with phylogenetic analysis further supporting its placement within the S. commune clade. To the authors’ knowledge, this is the first report of disseminated S. commune infection involving the central nervous system and lungs in a harbor seal. The case highlights S. commune’s potential to cause severe systemic disease in wildlife and emphasizes the value of integrating histopathological examination with molecular and phylogenetic analyses for accurate identification of fungal pathogens.