More scary stuff to keep you awake at night
Fungal Zombies
A friend who shares an interest in mushrooms suggested I watch a popular TV series based on a video game of the same name. The Last of Us is an apocalyptic science fiction story about a pandemic caused by a mushroom called cordyceps. Cordyceps is a genus of fungi numbering over 400 species, most of which parasitize a wide range of insect species.
We’ll dive deeper into this bizarre fungus a bit later, but suffice it to say, the lifecycle of this little club-shaped mushroom is creepy. What the cordyceps are capable of is much worse than just weird – it is horrific. But, if you are a human, you don’t have to worry about it – at least for now.
Certain world-altering events have happened in the past, others are happening as you read this article. Yet, still others may occur in the future. These things may be seemingly unrelated and unconnected by time and distance. However, if nature sees fit to bring these disparate factors together, humans, as a species, may be in big trouble.
The first event came right out of the sky
To put the pieces of this horror story together, we must go back some 65 million years to an event that killed off more than 70 percent of life on Earth in a relatively short period.
The Cretaceous – Paleogene mass extinction event, or K-T event, was precipitated by a nearly nine-mile-wide asteroid slamming into the submerged Yucatan Pe-ninsula in the Gulf of Mexico.
The impact energy consolidated into massive tsunami waves nearly three miles in height. However, that was just the immediate effect. Extinction would soon come to most life on our planet, including all non-avian dinosaurs.
Author’s note: I am reminded of a Gary Larson cartoon depicting several dinosaurs standing around smoking cigarettes. The caption says, “The real reason dinosaurs became extinct.”
When the asteroid plunged into the Gulf of Mexico, the intense heat vaporized the plentiful gypsum and sulfur in the matrix of the seabed. The resulting aerosol quickly expanded into the atmosphere, prompting an impact winter.
The dust-saturated atmosphere blocked most of the sunlight for years, possibly decades. Temperatures on Earth plunged as much as 55 degrees Fahrenheit within weeks.
Conditions resulting from the “impact winter” quickly began killing off the larger four-legged mammals. Photosynthesis of plants and plankton came to a screeching halt, causing further devastation to most herbivores and the predators that depended on them as a food source.
The impact winter began to subside when the atmosphere cleared, and the sun’s rays restored a warmer climate. But in the wake of the cold period, the Earth had lost millions of years in evolution and was devoid of dinosaurs, most birds, insects and many fish and shellfish.
Some of the cold-blooded (ectotherms) creatures survived. Crocodiles and sea turtles still share the planet with us because of their lower body temperatures and the physiological need to eat less frequently to maintain homeostasis.
The real winners of this catastrophe were the small warm-blooded (endotherms) mammals and fungi. This was particularly so among the subterranean mammals. The age of mammals was getting a solid foothold as the dominant animal on Earth.
The fungi had a different survival and expansion strategy. And it was delivered in the form of decomposing creatures and plants on a global scale. In the aftermath of the mass extinction event, Earth was temporarily nothing more than a chilly compost heap. The rotting mam- mals, fish, plants and dinosaurs, created a colossal windfall of nutrients for a lifeform specializing in breaking down organic material. Fungi would rise right alongside mammals to dominate planet Earth.
One can only imagine the stench during this transition from the age of dinosaurs to that of mammals. Likewise, the massive fungal bloom set the stage for rapid evolutionary growth and diversity of mushrooms. Yet, many sour-ces focus only on the rise of mammals after the dino-saur’s total and absolute demise, often ignoring the tremendous opportunities that fungi exploited post mass extinction.
Fungi do not require light and prefer cool temperatures; their Achilles’ Heel is higher temperatures, which is a fact that will come into play later in this article.
As one mycologist said, “If there are any other habitable planets in this universe, you can bet that there are fungi there.”
And that brings us to a discussion of one specific genus of fungi, the cordyceps.
It is a better human survival strategy to eat mushrooms rather than them eating us.
I have been collecting and eating edible mushrooms for nearly 70 years and never thought much about fungal pathogens. Of course, some mushrooms are deadly when consumed, and people mistakenly pick and eat them occasionally.
For example, Amanita phalloides, the fabled Deathcap, is responsible for 90 percent of deaths from poisonous mushrooms. Still, few mushrooms offer this level of toxicity, and there are less than 20 known mushrooms worldwide that can cause death.
Our forests here in the Appalachian Mountains offer a plethora of edible and delicious mushrooms, including the Chanterelle, Bolete, Lactarius, Oyster, Morel, Chick-en of the Woods and many more.
But then, there’s the psychopath of mushrooms, the cordyceps.
In his landmark book on Fungi, Mycelium Running – How Mushrooms Can Help Save the World, Paul Sta-mets describes how mushrooms can be used to clean up pollution such as oil spills, treat smallpox and flu viruses, restore damaged ecosystems, treat mental conditions such as an excessive fear of death when facing a fatal prognosis, and create novel and effective pesticides. And this is only a fraction of the potential uses of mushrooms.
It is fungal parasites we will now direct our attention to. Stamets has harnessed the power of one species of cordyceps to control carpenter ants as a successful pest control method.
How this works is one of the most fascinating stories in nature. The ants are infected by the microscopic spore of the cordyceps, penetrating the exoskeleton and gaining entry into the insect.
Once inside the host, the spores release compounds that exert muscular control over the ant, forcing it to do and act as the spore intends. And its intentions are clear; make the zombie ant leave its comfy nest for a humid and cooler location that favors fungal growth.
The spores continue rewiring the muscular system of the ant. After several days the ant is directed zombie-like to climb to the tip-top of a plant, where the muscles are further controlled to grasp the plant in a death grip, literally. The fruit bodies we call mushrooms devour the internal organs of the ant, killing it. Then the mushrooms erupt out of the now-depleted body to disperse its spores.
Of course, the ant is now dead, which makes the parasitic cordyceps a lethal predator, as the outcome of the infected insect is always fatal. Remember, mushrooms are in a category of their own; they are not plants nor animals, but rather, something in-between and having some aspects of both.
Several species of fungi function similarly to cordyceps. One species attacks flies in much the same way as cordyceps, including programming the fly to climb a plant. When the fly arrives at the precise location dictated by the fungus, it glues its mouth to the plant and turns “belly-up,” releasing plumes of spore from the fruiting mushrooms.
Another parasitic fungus, Massospora, specializes in infecting cicadas by invading the abdomen as the insect makes its way up to the ground’s surface to mate. Once inside the cicada, the fungus gains control of its motor functions, directing it to crawl and releasing spores as it does so.
The mere thought of a fungus taking control of our body and forcing us to do its will is abhorrent to most of us. It is even more repugnant to imagine bizarre-looking mushrooms sprou- ting from our skulls, as depicted in The Last of Us.
Imagine the horror and shock of waking up one morning to see that your spouse has club-shaped mushrooms protruding from their eye sockets. “Yuck! See you later, honey; I’m heading for work, and please don’t keep dinner warm for me; I’ll be late, real late!”
After the release of the TV series, one of the most frequent questions posed to Google was, “Can cordyceps infect humans?”
Well, can they?
No, cordyceps cannot infect humans or other mammals – but why, you ask?
It all has to do with the fact that we are warm-blooded creatures and, as such, are protected by a high core body temperature. The core temperature is the aggregate temperature of our internal organs, such as the brain, heart, liver and blood.
For humans, the core temperature falls in the range of 97.7 and 99.32 degrees Fahrenheit. Fungus thrives on high humidity and moderate temperatures, and the highest tolerable range is 77 to 86 degrees Fahrenheit. Our body temperatures are too high to support most fungal pathogens including cordyceps.
However, medical conditions can make humans more susceptible to several fungal pathogens.
According to the Yale School of Medicine, there is a “rising threat of fungal pathogens.” Other than fungal infections of the skin such as athlete’s foot (tinea pedis), severe fungal infections are becoming more frequent. Immunocompromised individuals from diseases like HIV, or transplant patients, are at greater risk from fungal infections like Aspergillosis, Histoplasma, Blastomyces and Coccidiosis.
An April 2023 article in National Geographic warns about a fungal pathogen of mysterious origin. According to the article, Candidas auris is quickly spread- ing around the world. It is difficult to detect in humans and even harder to treat.
Although fungal patho-gens rarely get past our immune system or survive our high core temperature, they are among the most challenging conditions to treat and can be fatal.
The alarm in the medical community rests in the fact that fungal pathogens have jumped from just infecting those creatures with little resistance, to humans whose higher body temperature may have evolved to resist fungal infections. The wall of protection from lethal fungal infections, in at least some cases, has been breached.
I prefer to close on a positive note. I urge you not to worry about weird mushrooms bursting out from your body like the creature in the film Alien. In fact, the species of cordyceps that infects one type of insect, say the carpenter ant, cannot infect another insect species.
Besides, the length of time it would take cordyceps to undergo the evolutionary changes required to infect humans would be many years away. By then, humans will have found another way to eradicate ourselves; we’re exceptionally good at that.
Postscript: I know that you are not really awake at night worrying about potential threats from mushrooms, nor do you have an abject fear of the next big asteroid heading our way from far out in our solar system.
Yet, we also acknowledge that there is an existential threat from a multitude of potentialities, both within and outside our planet. We just went through a trying global pandemic resulting from a disease that has jumped from animal to human with devastating results.
At the same time, we are facing a global climate change that has the potential for rewriting the history of our existence on this fragile ecosystem we call Mother Earth.
We have lost to extinction 99 percent of all creatures that have ever lived upon this Earth. Yet, we are the only life-form on Earth with the capability of changing our destiny. What we do now will determine whether we use our intelligence to mitigate and adapt to climate change, or go the way of the dinosaurs.
I implore you to think of our children and their children; they will pay the cost of our inaction.
Ken Springer
ken1949bongo@gmail.com
A big thanks to Dr. J for his invaluable insight into the complexities of the human thermo-regulatory system.
Citations include the National Library of Medicine, Yale School of Medicine, National Geographic, and the Stanford Medical Magazine, and are available upon request.