Fungus Among Us

August 23, 2012 at 2:27 pm | Posted in Climate change, Dysfunctional Politics, Global warming | 2 Comments
Tags: athlete's foot, Climate Change, disease, fungi, fungus, Global Warming, infection, toe nail fungus

Mold overwhelming tomatoes. Photo by Schimmel (Netherlands), obtained via Wikipedia (http://en.wikipedia.org/wiki/Mold).

In a previous post, I mentioned that global warming is likely to cause fungal diseases to become a major problem at non-tropical latitudes, where they have hitherto been only a minor problem.  This post will explain why.

Early in 2011 I attended a talk by Arturo Casadevall, who is the Chair of the Department of Microbiology and Immunology at the Albert Einstein College of Medicine, in Bronx, NY.  (His talk was unrelated to my work, and was given in a city far from New York.)

Cryptococcus neoformans, photomicrograph, provided to Wikipedia (http://en.wikipedia.org/wiki/Cryptococcus_neoformans) by Dr. Leanor Haley of the Centers for Disease Control and Prevention

The talk focused on cryptococcus neoformans, a fungus that presently causes over 600,000 human deaths per year.  But the talk also described in general how biological evolution and the typical temperature in a region jointly affect which organisms in that region are vulnerable to infection by many different types of fungi.

The most important factor is whether an animal’s internal temperature is or is not much warmer than the typical outdoors temperature.

Must species of fungi will evolve to thrive at the typical outdoors temperature.

That means that they will not thrive – and usually cannot survive – inside the body of an animal whose internal temperature is much warmer than is typical outdoors.

Toe nail fungus can grow under a human toe nail, but it cannot invade the interior of a human body, because we are warm-blooded, and our insides are too warm for the fungus to survive inside us.

The same is true of athlete’s foot.

Many colonies of bats in caves have been killed recently by white nose syndrome, which is caused by a fungus.  The bats are immune to the white nose fungus during the summer, when the bats are active, and the insides of their bodies are warm.  But infection by the white nose fungus can sweep a colony during the winter, when the bats hibernate, and the insides of their bodies are cool.

Little brown bat with white-nose syndrome in Greeley Mine, Vermont, March 26, 2009. Wikipedia.

Cold-blooded animals are much more vulnerable to internal infections by fungi.  One species of frog has recently become extinct due to fungal infection.  Insects are especially vulnerable.  A scratch on an insect’s body is very likely to lead to a fatal fungal infection.

Grasshoppers killed by Beuveria fungus
Stefan Jaronski, via Wikipedia, http://en.wikipedia.org/wiki/Fungus

Those statements apply today, at non-tropical latitudes.

But as the typical outside temperature rises at those latitudes, the fungi will evolve, and will become adapted to the higher temperatures.  People who live at those latitudes – and all other warm blooded animals who live there – will then become more vulnerable to internal infection by fungi.

That will happen without any planning or effort on the part of the fungi.  Every new generation of a particular species of fungus will a have a few individual new colonies which result from spores or buds which, due to random errors when the parent’s genetic code was copied while generating the spores or buds, would thrive in a warmer environment than would be optimal for the parent colony.  There will also be a few new colonies which would thrive in a cooler environment than would be optimal for the parent colony.  If the environment has warmed, then – on average – more of the warm-happy colonies will thrive and produce offspring.  Generation to generation, in small jerky steps, the bell-shaped curve of the temperatures that are optimal for that species will  jerk slightly toward higher temperatures more often than it jerks slightly toward lower temperatures.  Without knowing it, that species of fungus will adapt to a warmer environment.

By the way, this process – biological evolution – is so effective that software engineers now mimic it on computers, to generate computer algorithms that can function in complicated environments, and in changing environments.  Examples are Genetic Programming, artificial neural nets, and cellular automata.

How fungal infection will be affected by global warming is analyzed in more detail in two articles (references 2 and 3) that are cited in the section “Advantages and disadvantages of an endothermic metabolism” in an article in Wikipedia.

The pain to infected individuals and the economic cost of the increased fungal infection of humans, livestock, and wild animals should be included when weighing the near-term and long-term net costs of delaying action on climate change.