Rare Pathogen, Cryptococcus Gattii, Uses Divide And Conquer Strategy To Infect Healthy People

Spores
Certain fir species spread the spores of Cryptococcus gattii that can cause serious infections in humans and animals. Photo courtesy of Shutterstock

Our innate and acquired immune systems are our line of defense against invading pathogens — tracking and flushing out bugs that may cause diseases. But there are some organisms out there that have found ways to outwit these defenses, such as the recently discovered strain of fungus Cryptococcus gattii. This rare but deadly fungus uses the host body’s immune defenses to its own advantage; it uses it as a cover to proliferate and spread. And it does so by using the unique method of “division of labor,” or divide and conquer.

The pathogen is also unique because of the hosts it chooses. Not only immunocompromised people but healthy immunocompetent people also seem to be targeted by this pathogen. 

But the good news is you won’t catch it from the next person. "It is important to point out that the risk to any individual is still very low: The fungus is non-contagious and cannot be passed between humans, or indeed from animals to humans, so we're not presenting a doomsday scenario here,” said Professor Robin May, from the University of Birmingham, in a press release.

The research, published in Nature Communications, presents fascinating insights into how the fungus behaves inside a healthy body.

Modus Operandi

Whenever the body senses the presence of an invading pathogen it creates reactive oxygen species (ROS). These chemically reactive molecules form an important part of the host’s defense mechanism and work to prevent the spread of harmful pathogens by cleansing the body of invasive cells.

Healthy bodies generally have strong ROS reactions to pathogens. But they seem powerless in case of C.gattiThe fungus uses the release of the ROS signal to its own benefit triggering a "division of labor" in the intracellular fungal population.

"We don't often think of invasive cells working as a team, if you will, but this seems to be a smarter response," May said in the press release. "When they encounter ROS, the cells adopt different roles. Some sacrifice themselves for the benefit of others, and form a protective barrier that allows the rapid growth of neighbouring cells, allowing the establishment of the pathogen. This isn't something that we've seen before."

C.gattii spores are generally dispersed in the air from soil or leaves of certain tree species, such as eucalyptus and some fir species. Once inhaled, they enter the lungs and proliferate, using the "divide and conquer" strategy. They soon enter the blood stream from where they travel to other parts of the body. If they enter the central nervous system, they may cause life-threatening pneumonia or meningitis.

Manifestation of symptoms can take from two to 14 months. Treatment includes prescription antifungal medication for at least six months, while more serious cases may warrant the use of IV therapies with amphotericin B or flucytosine.

C.gattii is considered an emerging disease, with over 450 cases being reported in North America. First thought to be a disease of the tropics, it has now gained notoriety as being the cause of the largest ever outbreak of a life-threatening fungal infection in healthy people.

Epidemiologists are still trying to trace the route of migration of this particular lineage of the fungus. They believe it may have originated in the Amazon and spread due to climate change or through whales.

But May doesn’t buy that theory: "It's unlikely that climate change, or indeed whale migration, is behind this. However it got there, though, it really is a fascinating story of evolution. Cryptococcus gattii displays unique traits and has adapted to new environments in such a way that it presents us with a chance to make huge strides in understanding how these pathogens operate and, hopefully, make sure we are a well prepared to deal with future outbreaks."

Source:  May RC et al. 'Division of labour' in response to host oxidative burst drives a fatal Cryptococcus gattii outbreak. Nature Communications. 2014. 

 

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