Sources of C. gattii

Where does C. gattii live?

C. gattii lives in the environment, usually on trees, in tree hollows, and in the soil around trees.1,2 The fungus primarily lives in tropical and subtropical areas of the world.1,2 It also lives in mainland British Columbia, Vancouver Island, the U.S. Pacific Northwest (Oregon and Washington), and California. Some people from other parts of the United States have gotten C. gattii infections without traveling to the West Coast, suggesting that C. gattii may also live in other areas of the United States, such as the Southeast.36

Life cycle of C. gattii

C. gattii infections are not contagious. Humans and animals can become infected with C. gattii after inhaling dried yeast cells or spores in air. C. gattii travels through the airway and enters the lungs. The body’s temperature allows C. gattii to transform into its yeast form, and the cells grow thick outer layers to protect themselves. The yeasts then divide and multiply by budding. After infecting the lungs, C. gattii can travel through the bloodstream to infect other areas of the body, such as the central nervous system.

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Life Cycle of Cryptococcus gattii: Environmental Form, Host-associated Form, and Areas of Endemic for Cryptococcus gattii. Cryptococcus gattii lives in the environment (1), usually in association with certain trees or soil around trees. Humans and animals can become infected with C. gattii after inhaling airborne, dehydrated yeast cells or spores (2), which travel through the respiratory tract and enter the lungs of the host (3). The small size of the yeast and/or spores allows them to become lodged deep in the lung tissue. The environment inside the host body signals C. gattii to transform into its yeast form, and the cells grow thick capsules to protect themselves (4). The yeasts then divide and multiply by budding. After infecting the lungs, C. gattii cells can travel through the bloodstream (5)—either on their own or within macrophage cells— to infect other areas of the body, typically the central nervous system (6).

I’m worried that C. gattii is in the environment near my home. Can someone test the trees or soil to find out if the fungus is there?

Testing the environment for C. gattii isn’t likely to be useful. A sample that tests positive for C. gattii doesn’t necessarily mean that it’s a source of infection, and a sample that tests negative doesn’t necessarily mean that the fungus isn’t there. No tests are commercially available to detect C. gattii in the environment. Testing environmental samples for C. gattii is currently only done for scientific research, which is important because scientists are still learning about where C. gattii lives.

Species of Cryptococcus and genetic types of C. gattii

The genus Cryptococcus contains over 100 species. Because scientists are still learning about these fungi, their naming structure has been under debate recently. Cryptococcus neoformans and Cryptococcus gattii cause most cryptococcal infections in humans. Some research suggests that C. neoformans and C. gattii affect different patient populations. C. neoformans sometimes causes infections in healthy people, but most often causes meningitis in people who have HIV infection or who are otherwise immunocompromised. C. gattii affects healthy people as well as people who have weakened immune systems. It usually infects the lungs, the central nervous system, or both.

Cryptococcus gattii is actually a group of species called a species complex. The four most abundant species in this complex are Cryptococcus gattii, Cryptococcus deuterogattii, Cryptococcus bacillisporus, and Cryptococcus tetragattii. The different species of C. gattii can be found in different geographic locations. Most C. gattii infections in British Columbia, Canada, and the U.S. Pacific Northwest are caused by C. deuterogattii. In California and the southeastern United States, most infections are caused by C. gattii and C. bacillisporus. Cryptococcus deuterogattii appears to mostly cause lung infections, whereas the other types usually cause meningitis in people who don’t have any prior medical problems. However, scientists are still learning about the differences between the species of C. gattii. Most laboratory tests that identify C. gattii cannot distinguish between the other species in the species complex. At this time, additional testing is not necessary because the treatment is the same for all C. gattii infections.

References
  1. Springer DJ, Chaturvedi V. Projecting global occurrence of Cryptococcus gattii. Emerg Infect Dis. 2010 Jan;16(1):14-20.
  2. Harris J, Lockhart S, Chiller T. Cryptococcus gattii: where do we go from here? Med Mycol. 2011 Sep 22.
  3. Harris JR, Lockhart SR, Sondermeyer G, Vugia DJ, Crist MB, D’Angelo MT, et al. Cryptococcus gattii Infections in Multiple States Outside the US Pacific Northwest. Emerg Infect Dis. 2013 Oct;19(10):1621-7.
  4. Harris JR, Lockhart SR, Sondermeyer G, Vugia DJ, Crist MB, D’Angelo MT, et al. Cryptococcus gattii infections in multiple states outside the US Pacific Northwest. external iconEmerg Infect Dis. 2013 Oct;19(10):1620-6.
  5. Lockhart SR, Roe CC, Engelthaler DM. Whole-genome analysis of Cryptococcus gattii, Southeastern United States.external icon Emerg Infect Dis. 2016 Jun;22(6):1098-101.
  6. Springer DJ, Billmyre RB, Filler EE, Voelz K, Pursall R, Mieczkowski PA, et al. Cryptococcus gattii VGIII isolates causing infections in HIV/AIDS patients in Southern California: identification of the local environmental source as arboreal. external iconPLoS Pathog. 2014 Aug 21;10(8):e1004285.