First Case of Fungal Pyothorax in a Cat Linked to Clavispora lusitaniae

Fungal Empyema Thoracis Associated with Clavispora lusitaniae—First Report in a Domestic Cat

Radka Garnoeva, Velina Dinkova

Background
Empyema thoracis in cats is typically bacterial in origin, and fungal causes are rare, with only a handful of cases reported in the literature. Clavispora lusitaniae, a yeast formerly classified as Candida lusitaniae, is an emerging opportunistic pathogen in immunocompromised humans but has not been previously reported as a cause of feline pyothorax. This report describes the first known case of fungal empyema thoracis due to C. lusitaniae in a domestic cat, detailing the diagnostic and therapeutic approach.

Methods
A 3-year-old male outdoor European shorthair cat with a 7-day history of dyspnea and a 2–3 week period of lethargy and anorexia underwent physical examination, thoracic radiography, thoracentesis, cytology, bloodwork, and microbiological culture. Pleural fluid samples were cultured on standard media and analyzed using Gram staining and MALDI-TOF MS for yeast identification. The treatment included terbinafine antifungal therapy, clindamycin, furosemide, and supportive care, with follow-up evaluations over a 15-day period post-treatment.

Results
Radiographs showed bilateral pleural effusion and lung retraction. Cytology of the pleural fluid revealed lymphocytes, neutrophils, and macrophages. Initial bacterial cultures were negative, but fungal cultures produced white, non-haemolytic colonies, identified as C. lusitaniae via MALDI-TOF MS. Three thoracenteses were performed to evacuate pleural exudate. After a 15-day course of terbinafine, the cat’s clinical condition improved markedly, with normalized respiratory and heart rates, blood counts, and resolution of pleural effusion on imaging. No recurrence was noted at follow-up.

Limitations
The report presents a single case, limiting generalizability. No antifungal susceptibility testing was performed, and long-term monitoring beyond 15 days post-treatment was not detailed. A definitive source of infection was not identified, although environmental exposure was suspected.

Conclusions
This is the first documented case of feline pyothorax caused by Clavispora lusitaniae. Timely diagnosis using advanced microbial identification techniques and targeted antifungal therapy led to full clinical recovery. The report underscores the importance of considering fungal pathogens in atypical pyothorax presentations and highlights the potential zoonotic implications of emerging fungal agents in companion animals.

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