2. Sporothrix schenkii

Sporothrix species are dimorphic, saprophytic fungi widely distributed in the environment, primarily in soil, plant debris, wood, and the thorns of shrubs, most commonly rose bushes. Human infection typically occurs through minor skin trauma, such as puncture wounds from thorns or splinters, leading to direct inoculation of the fungus. For this reason, sporotrichosis has traditionally been considered an occupational disease, mainly affecting gardeners, agricultural workers, and individuals engaged in outdoor activities. Sporotrichosis occurs worldwide; however, most reported cases originate from tropical and subtropical regions of the Americas. In recent decades, zoonotic transmission has emerged as an important route of infection. Large outbreaks involving cat-to-human transmission, mainly caused by Sporothrix brasiliensis, have been documented in Brazil, highlighting the increasing epidemiological significance of animal reservoirs.

The most prevalent clinical manifestation of sporotrichosis is lymphocutaneous disease, accounting for approximately 75% of reported cases. This form is characterized by nodular and ulcerative lesions that develop at the site of inoculation and subsequently spread along lymphatic channels, producing the classic “sporotrichoid” pattern. Less common clinical forms include fixed cutaneous, disseminated cutaneous, mucocutaneous, primary pulmonary, and systemic sporotrichosis. Fixed cutaneous sporotrichosis presents as localized, crusted, or verrucous lesions that may heal spontaneously with residual scarring, most often affecting the face or trunk. Disseminated cutaneous sporotrichosis results from hematogenous spread or multiple inoculation sites and is almost exclusively observed in patients with impaired immune function, particularly patients with HIV infection.

The clinical presentation of sporotrichosis may mimic several infectious diseases, complicating diagnosis. The differential diagnosis includes atypical mycobacterial infections, especially Mycobacterium marinum, nocardiosis, tuberculosis, leishmaniasis, cat-scratch disease, anthrax, and other fungal infections such as chromoblastomycosis. Histopathological examination usually reveals granulomatous inflammation, while fungal elements are scarce and often undetectable. Therefore, tissue culture remains the diagnostic gold standard. The fungus exhibits dimorphism, growing as a mold on Sabouraud agar after 5–7 days of incubation at 25–30 °C. Microscopically, it shows delicate hyphae with numerous small ovoid conidia arranged in rosette-like clusters at the tips of conidiophores, resembling flower petals. Incubation on brain–heart infusion agar or broth at 37 °C for seven days results in the production of ovoid yeast cells, many of which display a characteristic “cigar” shape.

Molecular methods, including nested PCR targeting the calmodulin gene and sequencing of the rDNA internal transcribed spacer (ITS) region, allow reliable species-level identification and are particularly useful in cases with negative cultures or non-diagnostic histopathology. Two cryptic species pathogenic to humans, S. brasiliensis and S. globosa, have been distinguished from S. schenckii based on CAL gene sequencing, sugar assimilation profiles, and morphology. In the present case, molecular analysis identified an AFLP B-type S. schenckii strain, a genotype previously described in Colombia and Peru and associated with various clinical forms.

Treatment of sporotrichosis depends on the clinical form, host immune status, and species involved. Itraconazole is the first-line therapy for cutaneous disease. Terbinafine or potassium iodide are alternative options, whereas severe or disseminated infections require amphotericin B. Although sporotrichosis is rare in Europe and usually imported, heightened clinical awareness remains essential.

[Case editor: M. Drogari-Apiranthitou, Infectious Diseases Research Laboratory, 4th Dept of Internal Medicine, National and Kapodistrian University of Athens, published in Br J Dermatol, 2015. doi: 10.1111/bjd.13558]

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