Swamp cancer: a case of human pythiosis and review of the literature

Pythiosis is an infection caused by the aquatic oomycete Pythium insidiosum. Commonly known as 'swamp cancer' in veterinary pathology, pythiosis is now considered an emerging human disease associated with significant morbidity and mortality. However, because clinical information is limited, many healthcare providers, including dermatologists, are unfamiliar with this diagnosis. To increase awareness of this life-threatening infection, a case of cutaneous pythiosis is presented. We describe a middle-aged man with acute myeloid leukaemia who presented with necrotizing haemorrhagic plaques on his thighs after a weekend of freshwater boating. Histological examination of a biopsy specimen showed invasive fungal hyphae associated with dense perivascular inflammation and vessel damage. Diagnostic testing on tissue culture revealed growth of P. insidiosum. Despite multiple debridements and antifungal therapy, the patient died within 2 weeks of presentation. There are four clinical presentations reported in human pythiosis. Pythium insidiosum infection should be considered in any patient with a suggestive exposure history and fungal elements found on histological examination or in culture. Identification of the organism can be difficult, so polymerase chain reaction and serological assays can be useful in making a diagnosis. To improve clinical outcomes, early combination therapy with antifungals and surgery is needed.