Sporotrichosis: A brief review

Sporotrichosis is a chronic mycotic infection caused by dimorphic fungus Sporothrix schenckii, a common saprophyte of soil and plant detritus. According to recent phylogenetic studies, it is a complex of at least six cryptic species with distinct biochemical properties, geographical distribution, virulence, disease patterns, and therapeutic response. S. globosa is the commonest isolated strain in India and evidently responsible for most cases of treatment failure. The disease is endemic in tropical/subtropical regions with occasional large breakouts. In India most cases have been reported along the sub-Himalayan regions. The characteristic cutaneous and subcutaneous infection follows traumatic inoculation of the pathogen. Zoonotic transmission attributed to insect/bird bites, fish handling, and bites of animals is perhaps because of wound contamination from infected dressings or indigenous/herbal poultices and so is human-to-human spread. Progressively enlarging papulo-nodule(s) at the inoculation site develop(s) after a variable incubation period which will evolve into fixed cutaneous sporotrichosis or lymphocutaneous sporotrichosis. Primary pulmonary sporotrichosis following inhalation of conidia and osteoarticular sporotrichosis due to direct inoculation are rare forms. Persons with immunosuppression (HIV, immunosuppressive and anticancer therapy) may develop disseminated cutaneous sporotrichosis or systemic sporotrichosis particularly involving central nervous system. Clinical suspicion is the key for early diagnosis and histologic features remain variable. The demonstration of causative fungus in laboratory culture is confirmatory. Oral itraconazole is the currently recommended treatment for all forms of sporotrichosis but saturated solution of potassium iodide is still used as first-line treatment for uncomplicated cutaneous sporotrichosis in resource poor settings. Terbinafine has been found effective in the treatment of cutaneous sporotrichosis in few studies. Amphotericin B is used initially for the treatment of severe or systemic disease, during pregnancy and in immunosuppressed patients until recovery, and follow-on therapy is with itraconazole until complete (mycological) cure. Posaconazole and ravuconazole remain understudied while echinocandins and voriconazole are not effective.