Sporothrix schenckii and Sporotrichosis

Abstract

Sporotrichosis, which is caused by the dimorphic fungus Sporothrix schenckii, is currently distributed throughout the world, especially in tropical and subtropical zones. Infection generally occurs by traumatic inoculation of soil, plants, and organic matter contaminated with the fungus. Certain leisure and occupational activities, such as floriculture, agriculture, mining, and wood exploitation, are traditionally associated with the mycosis. Zoonotic transmission has been described in isolated cases or in small outbreaks. Since the end of the 1990s there has been an epidemic of sporotrichosis associated with transmission by cats in Rio de Janeiro, Brazil. More than 2,000 human cases and 3,000 animal cases have been reported. In humans, the lesions are usually restricted to the skin, subcutaneous cellular tissue, and adjacent lymphatic vessels. In cats, the disease can evolve with severe clinical manifestations and frequent systemic involvement. The gold standard for sporotrichosis diagnosis is culture. However, serological, histopathological, and molecular approaches have been recently adopted as auxiliary tools for the diagnosis of this mycotic infection. The first-choice treatment for both humans and cats is itraconazole.

Fig. 1.

Identification key for Sporothrix species of clinical interest, based on morphological and phenotypic tests described by Marimon and collaborators (152). PDA, potato dextrose agar; CMA, corn meal agar.

Fig. 2.

Cultures of pus from lesions of S. schenckii-infected patients. Most strains become visible after 4 days of growth on Sabouraud dextrose agar, presenting no visible dark pigment at this stage (tube at left), whereas others are melanized since the beginning of growth (tube at center). When transferred to brain heart infusion agar and cultured at 37°C, strains undergo dimorphism, presenting creamy white to tan yeast colonies after 7 days of growth (tube at right).

Fig. 3.

Glucose concentration-dependent increase of melanin synthesis. The concentration of glucose (%, wt/vol) in each culture is indicated by the numbers on the agar plates. S. brasiliensis strain 17307, grown at 22°C (A), and S. schenckii strain 23250, grown at 37°C (B), are representative isolates showing enhancement of melanization with increasing glucose amounts.

Fig. 4.

Melanin ghosts of S. schenckii 18782 strain under several culture conditions. (A) Cultures on minimal medium at 25°C yield melanin ghosts only from dematiaceous conidia. (B) When l-DOPA is added to minimal medium, both hyphae and conidia are melanized. (C) Yeast S. schenckii cells can also produce melanin in culture medium free of phenolic compounds or when l-DOPA is added. Bars, 10 μm.

Fig. 5.

Direct examination of clinical specimens for diagnosis of sporotrichosis. (A) KOH mount of a tissue fragment from a cat with sporotrichosis, showing cigar-shaped (arrow) and budding (dashed arrow) S. schenckii yeast cells. Note the high fungal burden in the specimen. (B) Direct examination (10% KOH) of the pus from a lesion of a human patient with sporotrichosis, showing nonspecific budding yeast cells. Bars, 10 μm. (Courtesy of Rosani Santos Reis.)

Fig. 6.

Geographic distribution, by country, of scientific production on sporotrichosis in the 21st century according to the type of publication.