Thursday, July 28, 2011

Cryptococcus gattii: Emerging fungal infection

Source: CDC


Cryptococcus gattii is a fungus that infects the respiratory tract of animals, including humans. C. gattii has been isolated from soil, trees, air, and water and is usually found in the eucalyptus trees of the tropics and subtropics. However, an outbreak of C. gattii in British Columbia, Canada, in 1999 resulted in the identification of the species on native trees of Vancouver Island, as well as surrounding soil and air, and spread to the mainland has been indicated. Recently, since 2004, outbreaks of infection in Oregon have prompted concern over this pathogen.

How infection occurs

Infection is caused when the spores of the fungus are inhaled. After taking up residence in the respiratory tract, illness can take 2-12 months to appear, but usually symptoms appear at 6-7 months after exposure. The lungs develop cavities and infiltrates from the fungus growing and taking up residence. It is also estimated that 20% of those who are infected develop meningitis because the infections spreads to the central nervous system. However, some infections are asymptomatic, in that the individuals do not develop symptoms.


Symptoms of Cryptococcus infection

The symptoms that occur with C. gattii infection vary greatly, but include: 

  • fever and chills
  • night sweats
  • weight loss
  • cough and shortness of breath
  • headache
  • chest pain
  • neck pain and stiffness
  • light sensitivity
  • decreased alertness (neurological symptom). 

Death is estimated to occur in less than 5% of human cases. However, the recent strain in Oregon (VGIIc) has an initial 25% mortality rate and the previous strain (VGIIa/major) had a 9% mortality rate.


Similar infections

A close relative to C. gattii is Cryptococcus neoformans, a more common human pathogen that acts as an opportunistic fungus that infects individuals with a depressed immune system (e.g., transplant patients, HIV/AIDS patients, the chronically ill). The two infections can be differentiated by lab workups on suspected cases. Cryptococcosis is infection with Cryptococcus fungus, and mainly considered to be the neoformans variety. However, the U.S. Centers for Disease Control and Prevention (CDC) consider C. gattii an emerging infectious disease. Lethal hybrids of the two strains have also been seen in recent years.

How to avoid Cryptococcus

Infection does not spread from person to person or from animal to animal, or even between humans and animals. The risk of infection is considered to be low, even for people living in endemic areas (only a couple hundred known North American cases over the last decade), but it is an environmental pathogen with no known risk factors for infection. Thus, no known way to prevent it. Most cases respond to anti-fungal medications, so early diagnosis and treatment is important.


The fungus grows on trees and can be found in the surrounding soil, air, and water. It is an environmental pathogen with no known risk factors for exposure and infection. The U.S. Centers for Disease Control and Prevention (CDC) do consider C. gattii an emerging infectious disease.


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