Thursday, 5 December 2013

Cryptococcuc gattii - Killer or Accident of Evolution?

A recent copy of the journal Scientific American reported on the strange incident of hundreds of dead dolphins suddenly being washed up on the shore of a remote island of the Pacific North West, their lungs filled with yeast!

This fungus family is well know to us and we have used it for thousands of years to help us make food & drink, so we know it is usually a benign friend, occasionally causing an irritating, superficial infection in many of us (Thrush) and sometimes causing serious infection but certainly nothing like this had been seen before.

This island infection outbreak spread to pets and even people, but this particular yeast had never been found on this island before nor anywhere close by - it is a native of the tropics which are many thousands of miles south of this island. So why did it suddenly become a virulent pathogen?

After a lot of work scientists have found this species living in places they weren't expecting to find it. It sounds like the yeast is quite widely present around the world and one reason for its spread north might be global warming. Perhaps the warmer environment is making it possible for some fungi to spread, perhaps the animals that live in those areas are becoming more vulnerable to infection because of climate change but regardless there does seem to be a trend to increasing numbers of fungal infections in some parts of the world.

Amoeba (magnified many times)
So why did it suddenly gain the ability to infect humans? Like many fungi it has a natural home in the rotting material on the ground and in that environment it has predators e.g. amoeba. Scientists are theorising that as the yeast develops the means to avoid being eaten by amoeba it may also have quite unwittingly also developed the means to avoid parts of the immune systems of animals, as parts of our immune system contains cells that look and act just like amoeba.A strain of yeast (C gattii) that can evade amoeba might also be able to avoid similar cells in the immune system of animals, and humans!

See a schematic of the infection cycle here.

This C. gattii outbreak is ongoing and work to discover how it happened is also ongoing.

Read the full article in Scientific American

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