Unmasking Prototheca wickerhamii: A rare case of cutaneous infection and its implications for clinical practice

Prototheca, an opportunistic pathogenic algae widely found in nature, has emerged as a potential public health concern. Most cases occur in immunocompromised individuals, with infections in immunocompetent patients being relatively rare. Due to their non-specific clinical presentation and limited awareness among clinicians, Prototheca infections are often misdiagnosed, resulting in delayed treatment. Recent advances in species identification and antifungal susceptibility testing have provided important tools for diagnosis and therapy. Here, we report a case of recurrent facial infection in a 76-year-old immunocompetent man. Skin biopsy revealed an infectious granuloma, and fungal culture identified yeast-like colonies. Fluorescence staining and scanning electron microscopy revealed abundant spores, while metagenomic sequencing confirmed the infection as Prototheca wickerhamii. The patient was successfully treated with long-term itraconazole and dipotassium glycyrrhizinate capsules. This case highlights the importance of early and accurate diagnosis in the management of Prototheca skin infections and reviews the therapeutic strategies used.