Dimorphic Fungi

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Dimorphic Fungi

• Histoplasmosis
• Blastomycosis
• Coccidiodomycosis
• Paracoccidiodomycosis
• Sporotrichosis

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Dimorphic Fungi

• There are five genera of dimorphic fungi
• Histoplasma capsulatum
• Blastomyces dermatitidis
• Coccidioides immitis
• Paracoccidioides braziliensis
• Sporothrix schenckii Subcutaneous

Systemic
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Dimorphic Fungi

• Dimorphic fungi grow in natural environments as
  saprobic molds
• When they gain entrance into the human body and
  cause an infection they grow as yeast, or in the
  case of C. immitis, as a spherule (round
  structure resembling a sporangium without
  sporangiophore within which spores develop

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Dimorphic Fungi

• These fungal pathogens can generally overcome the
  physiological and cellular defenses of the normal
  human host by changing their morphological form. 
  They are geographically or occupationally
  restricted.
• Human infections of the four most common systemic
  dimorphics is by inhalation of conidia from
  environmental saprobes
• Primary disease is in the lung but all can
  disseminate throughout the body to any organ
  system (i.e. systemic)

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Dimorphic Fungi

• Lab confirmation requires three (or four) steps
• 1. Detect and presumptively identify the tissue
  form (yeast?) in clinical specimens
• 2. Culture the mold form on primary media and
  identifying characteristic hyphae and conidia

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Dimorphic Fungi

• Lab confirmation requires three (or four) steps
• 3. Convert the mold form to tissue form (yeast)
  in vitro using rich media (usually containing
  blood and glucose) incubated at body temperature
• C. immitis requires a special medium incubated
  at 42o C in CO2)

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Dimorphic Fungi

• Lab confirmation requires three (or four) steps
• If the first three steps fail to definitively
  identify the organism, an exoantigen test can be
  done
• Many hospital labs send isolates to reference
  labs for this test
• It involves extracting water soluble antigens
  from young mold cultures

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Dimorphic Fungi

• Exoantigen test
• This is an example of a precipitin test in
  which a visible opaque lattice forms at the
  zone-of-equivalence. Monoclonal Ab is added and
  the lattice occurs where the concentration Ag and
  Ab are equal.
• An ouchterlony type double immunodiffusion
  procedure is usually used on a commercially
  available product.
• Ouchterlony can be ran in this manner or can be
  ran using patients serum bottled Ag in an
  attempt to detect Ab in a patients serum.

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Ouchterlony exoantigen test
Various monoclonal Ab types
Extracted soluble Ag from H. capsulatum