Sporothrix schenckii

Background

Dimorphic fungus with a hyaline, hyphated mold phase at 25ºC, and a round-to-oval budding yeast phase at body temperature
Produces melanin, a virulence factor

Common cause of nodular lymphangitis
Incubation period 7 to 30 days
Nodules can be 2 to 4 cm, and appear along the lymphatics, typically in the arms and legs (and face, in children)
- They become indurated, then ulcerated
May have regional lymphadenopathy
Usually mild or no systemic symptoms

Only occurs in patients with immunodeficiency, including alcoholism, diabetes, sarcoidosis, tuberculosis, transplantation, malignancy, immunosuppressive medication, or advanced HIV
Lesions can include ulcerations, aceniform, plaques, or crusts
Worst prognosis is with dissemination to lungs or meninges

Rare presentation without skin lesions, caused either by inhalation or deep inoculation
Musculoskeletal infections are the most common, with septic arthritis followed by osteomyelitis or tenosynovitis
Pulmonary sporotrichosis is more common in men aged 30 to 60 years, and presents similarly to pulmonary tuberculosis
Sporotrichotic meningitis is rare and occurs in immunocompromised patients
Can also affect eyes, genitals, or oropharyngeal mucosa

Direct microscopy
- May see yeast forms or characteristic asteroid bodies (especially from deep swabs
Culture
- Sab + chloramphenicol at 25ºC for 5 to 7 days for mold form followed by BHI at 35-37ºC for 5 to 7 days for yeast form
Molecular tests
- Some labs have developed PCR diagnostics
Serology
- Tube or latex agglutination have specificity (95%) and sensitivity (98-100%)
- Immunoassays also exist
Sporotrichin skin test
- Essentially like a TB skin test but for sporotrichosis
- Only useful for epidemiologic surveys