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• Guest speaker Dr Jeremy Day </aside>

• Cryptococcus spp. are environmental yeasts with a characteristic thick capsule

  • Capsule may protect it from free-living amoeba and other microbes

• Cause cryptococcal meningitis, a life-threatening disease with high mortality, despite well-defined treatment regimens, and often incomplete recovery in those who do survive

• HIV infection is a major risk factors for cryptococcal disease

Cryptococcus spp.

• Two main species of Cryptococcus cause disease in humans (50 species total):
  • Cryptococcus neoformans
  • Cryptococcus gattii
• C. neoformans causes infection in immunocompromised individuals whereas C. gattii predominantly causes infection in healthy hosts

Taxonomy

• Cryptococcus spp. are in the Basidiomycota fungal kingdom
• Two main species of Cryptococcus cause human disease, C. neoformans and C. gattii
  • These are further grouped into capsular serotypes, A-D
    • C. neoformans (formally C. neoformans var. grubii) = serotype A
    • C. deneoformans (formally C. neoformans var. neoformans) = serotype D
    • C. gattii = serotypes B & C

Epidemiology

• Cryptococcus neoformans is a ubiquitous environmental saprophyte found worldwide
  • Isolated from pigeon droppings, contaminated soil, and fruit (nitrogen rich sources)
  • Cryptococcus neoformans var. grubii (serotype A) causes >90% of human cases of cryptococcosis worldwide
    • Multiple lineages on genetic profiling, represented in most countries, but usually a dominant lineage in each country
  • Cryptococcus neoformans var. neoformans (serotype D) is found predominantly in Europe
• Cryptococcus gattii is an environmental yeast found in tropical and subtropical areas
  • Isolated from eucalyptus trees in S.E. Asia. In pacific N.W. associated with temperature rainforests
  • Endemic in northern Australia, Papua New Guinea and SE Asia; also found in Pacific Northwest, USA and parts of South America
• Cryptococcal disease (cryptococcosis) caused by C. neoformans most commonly occurs in patients with impaired T-cell immunity
  • HIV with CD4 < 100 cells/mm*3 is a major risk factor, accounting for 80-90% of infections
  • There are an estimated 150,000 cases of cryptococcal meningitis globally in HIV-positive individuals, resulting in 112,000 cryptococcal-related deaths
  • Rarely can cause infection in immunocompetent people - associated with a specific lineage of C. neoformans https://academic.oup.com/mmy/article/58/8/1149/5810715
• C. gattii mainly causes disease in apparently healthy hosts - an outbreak of hundreds of cases occurred in Vancouver Island and British Columbia between 1999-2013
• Potential for environmental exposure if pigeon dropping contaminating ventilation
  • Glasgow Hospital Cryptococcus cases

Pathogenesis

• Infection with Cryptococcus spp. follows inhalation of aerosolised, desiccated yeast cells or fungal spores from the environment