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

Found in soil, decomposing plant matter, and peat moss worldwide (but most often in moist tropical or subtropical zones)
- Increasing frequency in Italy
Acquired by traumatic implantation or inoculation of a preexisting wound
Can also be acquired by cat scratches
Hosts include humans, cats, horses, dogs, rodents, cattle swine, camels, etc.

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
- Can be in the context of HIV IRIS
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
- Major risk factors: alcohol (1/3); sarcoidosis, TB, or diabetes (1/3); otherwise healthy (1/3)
Sporotrichotic meningitis is rare and occurs in immunocompromised patients
Can also affect eyes, genitals, or oropharyngeal mucosa

Sample collection
- Deep swab or aspirate, if possible
- Punch biopsy, can be with sterile saline if needed (not in formalin)
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
- Colony appearance is a white mold that becomes dark
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

First-line: itraconazole 100 to 200 mg po daily until 2 to 4 weeks after the lesions resolve (around 3 to 6 months)
- Dose may be increased to 400 mg if there's a poor response, there are extracutaneous infections including osteoarticular or pulmonary disease, or the host is immunocompromised
- Check for drug-drug interactions
Alternatives include amphotericin B, fluconazole, and maybe terbinafine
Can also do local hyperthermia, especially for patients who are unable to take the above medications

For pregnant women, use amphotericin B
For osteoarticular infections, use itraconazole 200 mg po bid
- Can use amphotericin B as induction
- Duration is at least 12 months
For severe pulmonary infection, use amphotericin B 3 to 5 mg/kg daily (liposomal), stepped down to itraconazole 200 mg po bid when better, to complete at least 12 months total
Same treatment for disseminated disease
For meningeal infection, use amphotericin B 5 mg/kg daily for 4 to 6 weeks, followed by itraconazole 200 mg po bid until at least 12 months
For children, use itraconazole 6 to 10 mg/kg (max 400 mg) daily
For severe disease in children, use amphotericin B 0.7 mg/kg daily induction then itraconazole 6 to 10 mg/kg (max 400 mg) daily