Sporotrichosis 

Sporotrichosis is a subacute or chronic infection caused by the soil fungus Sporothrix schenckii. Although only one species of Sporothrix was classically identified, modern phylogenetic studies suggest the geographic distribution of multiple distinct Sporothrix species.^[1] The characteristic infection involves suppurating subcutaneous nodules that progress proximally along lymphatic channels (lymphocutaneous sporotrichosis). Primary pulmonary infection (pulmonary sporotrichosis) is rare, as is direct inoculation into tendons, bursae, or joints. Osteoarticular sporotrichosis is caused by direct inoculation or hematogenous seeding. In rare cases, disseminated S schenckii infection (disseminated sporotrichosis) occurs, characterized by disseminated cutaneous lesions and involvement of multiple visceral organs; this occurs most commonly in persons with AIDS.

Infection with the dimorphic soil fungus S schenckii is usually acquired through cutaneous inoculation. See the image below.

The initial reddish, necrotic, nodular papule of cutaneous sporotrichosis generally appears 1-10 weeks after a penetrating skin injury. The lesion is a suppurating granuloma that consists of histiocytes and giant cells, with neutrophils that accumulate in the center and that are surrounded by lymphocytes and plasma cells.

The S schenckii infection spreads from the initial lesion along lymphatic channels, forming the chain of indolent nodular and ulcerating lesions typical of lymphocutaneous sporotrichosis.

Other tissues are involved by direct extension and, less often, by hematogenous dissemination. The most common extracutaneous infection sites are in the bones, joints, tendon sheaths, and bursae. Hematogenous dissemination—particularly in immunocompromised hosts—results in widely disseminated cutaneous and visceral infection, including meningitis.

A rare form of sporotrichosis appears to result from inhalation of the organism. This form is characterized by a chronic cavitary pneumonia that is clinically and radiographically indistinguishable from tuberculosis and histoplasmosis. This form of sporotrichosis is most common in individuals with severe underlying chronic obstructive pulmonary disease (COPD). Sporotrichal infection of the larynx and paranasal sinuses has also been described.

Frequency

United States

The incidence of sporotrichosis is not precisely known but is estimated at 1-2 cases per million population. An estimated 200-250 cases occur per year.

International

Sporotrichosis occurs worldwide, with focal areas of hyperendemicity. The global incidence is unknown. In the highlands of Peru, the incidence of sporotrichosis is approximately 1 case per 1000 people.^[2] China is a serious endemic region.^[3]

Mortality/Morbidity

• Spontaneous resolution of cutaneous and lymphocutaneous forms of sporotrichosis has been documented.
• The prognosis is excellent for complete recovery after therapy, although the response to therapy may vary.
• Pulmonary sporotrichosis may contribute to declining pulmonary function in patients with COPD.
• Osteoarticular sporotrichosis may result in significant morbidity in the form of chronic osteomyelitis and arthritis with significant loss of joint function and deformity.
• Disseminated sporotrichosis is associated with significant morbidity and, possibly, mortality in immunocompromised hosts.

Race

Sporotrichosis has no known racial predilection.

Sex

Sporotrichosis is slightly more common in males than in females, presumably due to an increased exposure risk rather than to a difference in susceptibility.

Age

In developed nations, sporotrichosis is most common among adults. However, in tropical regions and in areas of hyperendemicity, sporotrichosis may be more common in children and adolescents. For more on pediatric sporotrichosis, see the article Sporotrichosis in eMedicine’s Pediatric: General Medicine volume.