Is Fungus The Next Doomsday Killer?

Infected person stuck to the wall and completely transformed by Cordyceps fungus.

HBO’s current hit series, “The Last of Us,” debuted on Jan. 15. In it, creators Craig Mazin and Neil Druckmann portray a beautiful nightmare where an elaborate network of thriving parasitic fungi cause a global pandemic.

How real is this fictional show when compared with reality?

There is a genuine threat from fungi, but they provide many benefits as well. There are hundreds of thousands of fungi species, 600 or so discovered in the Cordyceps genus as of today. First discovered in China and used as medicine, it was believed by an emperor that digesting infected silkworms held the key to a longer life.

The history we know of Cordyceps dates back as far as the Ming Dynasty (1368-1644) and is mentioned in the Huang Di Neijing, otherwise known as the Chinese bible of medicine. Now, Ophiocordyceps Sinensis is specifically used for cancer treatments and a wide range of ailments in Chinese medicine, which is currently rare due to the difficulty in cultivation.

In addition, it’s because of fungi that we have everyday essentials such as penicillin, cheese, beer, and other commonly used products. Fungus also has a living cell structure, unicellular and multicellular, compared to a virus that is not living. So it needs a food source, and for the particular species mentioned in the show, insects are the primary source of nourishment.

That’s not to say that reptiles and mammals can’t become host to fungi because they can, indeed, just not by Cordyceps currently. Arthrobotrys is a predator of nematode worms. By snaring and trapping them, hyphae begin to grow through the worm and consume it from within. So overall, besides getting sick with a range of symptoms, the zombie-like mind control is more fiction than reality.

According to Biology Professor Rikki Edelman, certified Horticulturist and member of the Mycological Society of San Francisco, “even if there were to be a Cordyceps fungus attacking a human body, it would have a hard time breaching the internal walls and bones required to reach the human brain and numerous systems it would need to infect which is all highly unlikely. The show depicts what looks to be an amalgamation of fungi as it is growing everywhere, on the walls of buildings and through people.”

For this to happen in people first, according to Chabot College Microbiologist Robert Cattolica, who holds a (Ph.D.) in Pharmacology and Toxicology as well as a (BA) in Molecular Cell Biology, “there would need to be a rare crossover event, where the reason would be unknown to science. This crossover event would be something like going from an ant to a wasp or a small mammal.”

In the show, it is implied that climate change was the culprit in forcing adaptation to a warming planet where the fungus can then withstand the temperatures of the human body. This factor is stated as “being a real possibility where climate change and deforestation can destroy species or a food source and create the need for a new one. This, however is very unlikely in Cordyceps as it has evolved alongside its food source, which is mainly different insect species. This would take numerous exposure events on the part of humans to provide the opportunity for adaptation in the body. Not to mention the amount of tissue the fungus has to infect which is elaborate and extensive compared to the body of an ant.

“It would be more likely to infect a certain area of the body like the liver or mucus membrane. Spores being the optimal delivery mechanism and more infectious through ingestion compared to the biting depicted on the show” said Professor Cottalica.

Which fungi are currently dangerous to humans?

“The Cordyceps in the show seems to ignore animals and lacks the spore element that is extremely vital to fungus reproduction,” said Professor Edelman. The Cordyceps Militaris Fungus hijacks the body of ants mainly, filling it with a biomass of mycelium. It is a gruesome sight close up, the ant is flooded with chemicals and compelled to climb to a great height where it will perch and die until the fungus has fully formed and prepared to spore beginning the next life cycle.

In humans, spores are deadly and can cause long term respiratory illness or acute respiratory failure. This fungus is more commonly known as mold which can be found just about anywhere. More alarming is the 2009 discovery of Candida Auris which grows as yeast and is anti-fungal resistant. This fungus has climbed in infection rate, spread to several continents and is currently being tracked by the CDC. This fungus can cause illness and death in horrific ways, especially for people with immune deficiencies. Climate change is having a huge impact on the future of fungi, where the line that separates humans as hosts is starting to disappear. “Resistance is old in the fungi’s defense because antibiotics are used by fungus at war with each other to kill,” says Professor Cattolica.

Candida is super communicable in the form of spore dispersal which can be a problem for patient treatment in hospitals. There is even the possibility of being mistreated as infection from Candida can be hard to identify and made worse. Then there is Claviceps Purpurea which is an Ergot fungus that can cause hallucinations, nausea, vomiting, gangrene, spasms, convulsions, unconsciousness, and death. It grows on the ears of rye and can contaminate grain and seeds. This fungus was believed to influence the madness behind the Salem Witch Trials. These are just some of the known fungi dangerous to humans as science is still discovering unknown species and unseen behaviors from the fungi kingdom.

Can this fungus outbreak be engineered?

Humans have been known to experiment on just about everything and fungus is not exclusive. Anthrax and Smallpox are good examples although not directly fungi related. “If I was a mad scientist, I would bet on a virus over fungi as it is already designed to kill humans by nature. There needs to be significant breakthroughs and human experimentation that would need to take place for this type of engineering,” said Professor Cattolica. There are examples of this on a commercial scale as most of the safe products in one form or another can be purchased and used for pest control.

Cordyceps fungus can be used for insects and Arthrobotrys for nematodes. Because of the super combined elements of the show’s fungus, it has mixed characteristics when it comes to the infected people we have seen so far. For instance, the fungi located on the split heads, arms and necks of it’s victims are more shelf-like. According to Professor Edelman, “they look more related to the fungus Ganoderma, known as Reishi, which has healing properties for humans including cancer. This fungus can be very deadly for trees causing root and stem rot, yet safe everyday products are derived from this fungus and taken directly by humans for medicinal purposes. If you drink a coffee, you don’t become a coffee.”

Edible mushrooms are used on a daily basis for cooking or your pizza toppings. So the jury is still out on future possibilities, “as there are still so many functions never observed by science in the fungi kingdom,” said Professor Cattolica. Overall the show is really good from the opinion of these biology professors and brings a much-needed interest to the world of biology and climate change.

HBO’s “The Last of Us” show details

"The Last of Us," key art/main promotional material.

No spoilers: “The Last of Us” depicts a zombie-like outbreak caused by a Cordyceps fungus that initially grows with substrates in flower, grain, and bread factories. It stars Pedro Pascal as Joel and Bella Ramsey as Ellie portraying an unlikely pair forced to come together by chance. Joel must get Ellie to a destination in this post-apocalyptic world safely. The show currently sits at 97% on Rotten Tomatoes and has already been renewed for a second season, announced after the airing of only the second episode. Airing on Sunday evenings, becoming successful overnight, the show now boasts a viewership of twenty-two million and growing, making it the second biggest premiere for HBO in a decade.

Image courtesy of Liane Hentscher

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