MICROBIOLOGY

• Yeast-like, round fungus; usual size is 5-10µm with polysaccharide capsule [Fig].
  • Reproduces by narrow-based budding.
• Epidemiology: worldwide in soil, high levels in pigeon droppings (but this relevance is questionable for human disease).
• Two species:
  • C. neoformans historically divided into four serotypes (A to D) described based upon the capsule components with 2 species and 2 varieties causing human disease. Now based on genotypic evaluation, proposed:
    • Serotype A: now known as C. neoformans v. grubii
    • Serotypes B and C: C. gattii
    • Serotype D: C. neoformans v. neoformans (most common) and worldwide in distribution
      
  • C. gattii: more recently detected and seen primarily in Australia, Western Canada and the northwestern U.S. (Washington and Oregon).
    • Clinical presentation, diagnosis, and treatment are the same as with C. neoformans.
    • Differences from C. neoformans include higher attack rates in healthy hosts and worse prognosis.
    • It appears more resistant to fluconazole.
    • The true extent of infection/epidemiology is not known.