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.