Introduction
Background
Sporotrichosis is a subcutaneous or systemic infection caused by Sporothrix schenckii, a rapidly growing dimorphic fungus. The organism derives its name from R B Schenck, who first reported the infection in 1898. Sporothrix species typically exist as a saprophytic mold on vegetative matter in humid climates worldwide. A dimorphic fungus, the organism exhibits mycelial forms at 25°C and a yeast form at 37°C.1,2,3
Cutaneous infection often results from a puncture wound involving infected cats, thorns or other plant matter. Other more unusual reported causes include insect stings, squirrel bites, and trauma induced by liposuction.4,5 Any compromise of the skin barrier with subsequent seeding could potentially cause infection. Sporotrichosis usually occurs sporadically as isolated cases. Occasionally, groups of individuals are infected after being exposed to the organism.6,7,8
Since approximately the beginning of the 21st century, an outbreak of increasing numbers of cases has been occurring in Rio de Janeiro, Brazil. From 1998-2004, 759 culture-proven cases have been identified and treated, predominantly among women at a median age of 39 years and predominantly among those with domiciliary or professional contact with infected cats.6
An outbreak in the United States in 1988 affected 84 people who handled sphagnum moss.8 An unusually large outbreak occurred in Africa in the 1940s in more than 3000 miners who had frequent physical contact with wood timber supports. This contributed significantly to the current understanding of Sporothrix schenckii, its growth patterns, and its mechanisms of dissemination.2,3
Pathophysiology
Sporotrichosis infections can be either cutaneous or extracutaneous. Cutaneous infections are most common and are subclassified into fixed cutaneous and lymphocutaneous. A few authors refer to a rarely included third subclass of cutaneous sporotrichosis in which diffuse cutaneous involvement occurs.
Fixed cutaneous infections occur at the site of inoculation and remain confined entirely to the skin. Lymphocutaneous disease results from lymphangitic spread of an infection. Satellite lesions develop along the path of the lymphatic vessels (sporotrichoid spread) and associated lymphadenopathy occurs. Extracutaneous, or disseminated sporotrichosis, can present as pyelonephritis, orchitis, mastitis, synovitis, meningitis, or osseous infection.1,2,3,9
Sporotrichosis can cause a monoarthritis, typically involving the knee.10,11 Many affected individuals are immunosuppressed by alcoholism or HIV infection.12,13,14 Pulmonary involvement is rare.2,3
Under study is the mechanism of pathogen-host interaction, including a 70-kd (Gp70) glycoprotein from the cell wall of S schenckii, which is involved in fungal adherence to the dermal extracellular matrix.15 This protein shows promise as a possible target for passive immunity therapies.16
Frequency
United States
The incidence of sporotrichosis is unknown. As an unreported, sporadic disease, its incidence is difficult to estimate. The mold itself is endemic to the Missouri and the Mississippi River Valleys.2,3
International
Sporotrichosis is the most common subcutaneous mycosis in South America. Most reported cases occur in Mexico, followed by the remaining Americas, Australia, Asia, and Africa. Sporotrichosis is rare in Europe.2,3
Mortality/Morbidity
The morbidity of cutaneous infections is generally low, although therapy can be prolonged and can have potentially serious adverse effects. Scarring can result at ulcerated sites.1 Systemic infections can be life threatening, especially in the immunocompromised host.2,12,13,14
Sex
In the past, males were affected more often than females due to occupational-related risks for puncture wounds. With the 1998 outbreak in Rio de Janeiro, Brazil, women with exposure to infected cats currently account for the predominant number of new cases.2,3
Age
Sporotrichosis may occur in any age, but it typically affects adults, reflecting their more frequent participation in veterinary care, gardening, woodworking, and occupational situations in which puncture wounds may occur.2,3,6,7,8
Clinical
History
Most patients relate a history of a recent prick injury at the site of infection. Clinical disease usually becomes apparent within 3 weeks of injury; however, the interval from injury to apparent infection may be as long as 6 months. The injuries are attributed to a variety of causes, including rose thorns, hay, sphagnum moss, conifer needles, mine timbers, and infected cats. The characteristic skin lesion is a dermal or subcutaneous nodule that may ulcerate. As the infection spreads along the regional lymphatic chain, satellite nodules develop along with associated regional lymphadenopathy. The infection may disseminate to cause systemic disease.1,2,3
Physical
Lymphocutaneous sporotrichosis is the most common presentation. Symptoms usually arise within 3 weeks of injury. A subcutaneous nodule develops at the site of inoculation and may ulcerate as the result of central abscess formation. Satellite lesions form along the associated lymphatic chain and lymphadenopathy subsequently develops.1,2,3,6,7
Close-up of an ulcerated nodule reveals the satellite lesions characteristic of lymphangitic (sporotrichoid) spread.
Fixed cutaneous disease also is known as nonlymphatic sporotrichosis. This appears as a scaly, acneform, verrucous or ulcerative nodule that remains localized. Satellite lesions and lymphadenopathy do not occur in this form of sporotrichosis. Fixed cutaneous lesions may rarely resemble pyoderma, rosacea, pyoderma gangrenosum, and keratoacanthomas.1,2,3,6,7,17
Disseminated disease can result in pyelonephritis, orchitis, mastitis, arthritis, synovitis, meningitis, osseous infection, or, rarely, pulmonary disease. Cutaneous lesions can occur in the setting of disseminated infection.1,2,3,6,7
Clinical signs and symptoms may be blunted in the presence of elevated glucocorticoid states or systemic steroid therapy. Sporotrichosis in this setting has resembled erysipeloid cellulitis.12
Causes
Sporotrichosis is caused by S schenckii, a dimorphic fungus.1
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References
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