Sporothrix schenckii
Shmuel Shoham, M.D.
MICROBIOLOGY
MICROBIOLOGY
MICROBIOLOGY
- There are numerous Sporothrix species, but only a few cause human and animal diseases.
- S. brasiliensis: Limited to South America, associated with cat-transmitted disease and environmental (non-zoonotic) acquisition of infection.
- S. globosa: Worldwide distribution, but most prevalent in East Asia. Infection is associated with the inoculation of contaminated plant matter. A case of infection after a cat scratch in Japan has been reported.
- S. schenckii (sensu stricto): It has a worldwide distribution. Similar to S. globosa, infection is associated with inoculation of contaminated plant matter. The cat-transmitted disease has been described, including in the U.S.
- S. luriei: Limited to Africa and Asia. Less pathogenic than others.
- S. mexicana: As implied by the name, causes infection in Mexico.
- Dimorphic fungi:
- Room temperature (25-28 C): Grow in filamentous form with septated hypha and conidia.
- Body temperature (36-37 C): invasive, cigar-shaped yeast 1-3 x 3-10 µm.
- Exposure to the fungus: Multiple exposures and infections can arise from a single source.
- Zoonotic (with S. brasiliensis): Infected cats can have a high fungal burden and transmit S. brasiliensis directly through scratching or biting.
- Sapronotic (all non-brasiliensis Sporothrix species): Transmission is from contaminated plant matter or soil to people via minor cuts or scrapes. However, case reports of cat-to-human transmission with some of these species.
- Stains
- Testing exudate for the presence of asteroid bodies (yeasts surrounded by immune material, Splendore–Hoeppli phenomenon) is a low-cost and sensitive diagnostic method.
- Exudate material is placed on a slide with saline and a 10% formaldehyde solution drop and examined by microscopy.
- Yeast phase [Fig 1]
- Fluorescent antibodies for tissue staining or culture confirmation [Fig 2].
- Histopathology: Important stains are PAS and Gomori-Grocott stains [Fig 3].
- Typical characteristics are yeast cells, asteroid bodies (although not pathognomonic for sporotrichosis)
- Histological patterns termed sporotrichoid, tuberculous and foreign body reactions.
- Culture of infected material (pus, secretions, tissues) is the gold standard for diagnosis.
- Use Sabouraud dextrose at 28 C for 5-8 days to grow the filamentous form.
- Use blood chocolate or blood BHI agar at 37 C to grow the yeast form.
- Nucleic amplification tests (e.g., PCR)
- Used to identify the organism when grown in culture to the species level.
- NAT testing directly from clinical samples (before growth in culture) is used in research settings.
- Antibody blood tests are in development and are starting to be employed in Brazil.
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