Can a Fungi Apocalypse Happen?
Cesar Collado
March 13, 2023
The Last of Us Onscreen

HBO MAX’s “Last of US” Stretches Some Interesting Fungus Facts

Recently, I have received many questions regarding the possibility of a “fungal apocalypse”.  The HBO Max series, “The Last of Us,” depicts a fictional scenario where a fungal infection, Cordyceps fungus, mutates and invades the brains of humans, turning them into aggressive creatures. This is pure fiction created by embellishing some truths.  However, there are real-life examples of fungi that can invade and live inside other organisms, and there are some interesting Fungus facts that provide the TV show material for a fictional narrative.

Mold is a remarkably resilient organism that can cause allergies (allergen), infections (pathogen), or toxicity (mycotoxin). There are some species of fungi that can cause diseases in plants, animals, and even humans. These fungi can invade the tissues of their hosts and cause a variety of symptoms, ranging from mild skin infections to life-threatening illnesses. Fungal infection can take a variety of forms: on the skin, sinuses, lungs, stomach, fingernails, toenails, exposed membranes in the eyes, mouth, open wounds, and even colonize in the brain.  Mycotoxins, secondary metabolites excreted by some molds, if present inside the body at very small levels, can be toxic to the brain and other organs, and can disrupt many bodily functions. A fungal infection in the bloodstream can be fatal.

Here are some interesting fungi facts that set the stage for fictional stories.  I hope these fungi facts also emphasize the unlikely nature of these fictional stories.

Fungi Fact 1:  Fungal Colonization. Some Fungi Interconnect

When water, oxygen, and mold spores meet organic material, mold reproduces rapidly into colonies.  Colonies can grow indefinitely.  Mold growth spreads through thread-like structures called mycelium. Mycelium is made up of thin, branching strands called hyphae, which grow and spread through organic matter in search of nutrients.  The organic matter can include plant, animal, or human tissue.

Mycelium interconnectivity amongst fungi, Fungus facts

These hyphae can form a vast network that can connect multiple individual mushrooms, allowing them to share resources and communicate with each other. This network is often referred to as a “mycorrhizal network”, and it plays an important role in the health and survival of many plant and fungal species. Through this network, mushrooms can share nutrients and chemical signals with each other, allowing them to coordinate their growth and respond to environmental changes. This network also helps to distribute nutrients and water throughout the ecosystem, which can benefit other plants and organisms as well. The same phenomena occurs with  building materials.  Water damage can be frightening when considering implications.

Fungi Fact 2: The World’s Largest Living Organism is a Fungus

The largest living single organism known on Earth is a mushroom that occupies some 2,384 acres. The largest fungi in the US is the Honey Mushroom (Armillaria Ostoyae). Here are some interesting fungi facts.  It covers an area of approximately 3.5 sq. mi., 2,384 acres (965 hectares) in the Malheur National Forest in eastern Oregon. The fungus is estimated to be at least 2,400 years old, possibly up to 8,650 years old, making it one of the oldest and largest living organisms on Earth. The Honey Mushroom is a parasitic fungus that feeds on the roots of trees, and can cause extensive damage to forests. It is also capable of producing large fruiting bodies.  These mushrooms are edible but not commonly consumed due to their bitter taste.

Armillaria Ostoyae- Worlds largest living organism, Fungus facts

Source: USDA Brochure:  Malheur National Forest.  Oregon.

Fungi Facts 3: About Cordyceps, The Fungal Villain in “The Last of Us”

The premise of the new television show based on the video game The Last of Us in which, as a result of warming temperatures caused by climate change, a fungus takes over the world and turns humans into parasite-controlled zombies.

The Cordyceps fungus is a type of parasitic fungus that typically infects insects, spiders, and other arthropods. There are over 400 species of Cordyceps fungi, each of which has adapted to infect and parasitize specific host species.

The life cycle of Cordyceps fungi typically involves the spores of the fungus infecting an insect or other arthropod, and then growing inside the host’s body. The fungus eventually consumes the host’s tissues, replacing them with fungal mycelium, and eventually produces a fruiting body or “mushroom” that emerges from the host’s body. 

Fungi, Cordyceps, changing ant behavior, Fungus factsOne species of Cordyceps, Ophiocordyceps unilateralis, is known to infect and manipulate the behavior of ants. The fungus invades the ant’s body and grows inside it, eventually causing the ant to climb to the top of a plant and die. The fungus then releases spores from the ant’s body, which can infect other ants and continue the cycle.

Cordyceps fungi have also been used in traditional medicine for centuries, particularly in Chinese and Tibetan medicine. Some species are believed to have health benefits, such as boosting the immune system, improving energy levels, and reducing inflammation. However, more research is needed to fully understand the medicinal properties of Cordyceps fungi.


Fungi Facts 4:  The Most Common Fungal Invader to Humans is Candida 

Candida overgrowth, also known as candidiasis, is a relatively common condition caused by an overgrowth of the yeast Candida in the body. Candida is part of our microbiome and a normal inhabitant of the human gut and mucous membranes. When it grows unchecked, it can lead to a range of symptoms and health problems.  The most common candida overgrowth infections include thrush (Mouth and Tongue), Vaginal Yeast Infection, and Toenail Fungus.

Common fungal infections, Fungus facts

Fungi Fact 5: Spore Counts Can Be in the Billions

Individual mold spores are less than 4 microns in size – They are so small that as many as 250,000 spores can fit on a pinhead and a person can inhale as many as 750,000 of these spores per minute.  Disruption of even small mold colonies can result in millions of spores being released into the immediate air.

Mushroom puffball spreads billions of fungal spores, Fungus facts

Source: Operating Engineers National Hazmat Program on Mold Awareness

Fungi Fact 6: Water Damaged Furnishings are Common Sources for Mycotoxin Producing Molds

Preventative measures for the growth of fungi that produce potent mycotoxins is an important consideration when facing indoor water damage or flooding. Consider the following about these toxic fungi:

  • They are seldom abundant in outdoor ambient air unless disturbed.
  • Most toxic exposures occur from the indoor growth of toxin-producing fungi related to excessive moisture and ‘man-made’ building materials.

There is a growing body of evidence that indoor mold issues such as water damage to common building materials have a much greater propensity to harbor toxic mold and mycotoxins. Drywall, particle board, upholstery, carpet, and carpet padding absorb and maintain moisture while serving as a significant food source for mold. Mold can begin to reproduce in as little as 24-48 hours unless properly removed and/or dried with proper equipment.

Mycotoxins from living molds are semi-volatile chemicals that travel on mold and mold fragments. Mold debris is still a potentially harmful allergen or may contain traces of mycotoxins it has produced.  Mold debris must be removed via HEPA vacuuming or other cleaning methods (e.g. – wet wiping) before a room is judged to be clean.  Mycotoxins and fragments of many molds will often remain toxic. Read about what it takes to detoxify from mycotoxins HERE.


Scientists consider the possibility of a human parasitic fungus as purely science fiction:

  • The fungi that infect insects would require millions of years of genetic changes to evolve enough to infect humans.
  • Each of the known zombie fungus species have evolved to match a specific insect, and each unique strain has little effect on other organisms. 
  • “A cordyceps that evolved to infect an ant in Thailand can’t infect a different ant species in Florida.” Ian Will, a fungal geneticist at the University of Central Florida

In summary, for the fungus to move to any warm-blooded animal would require some serious evolutionary work.

  1. Gibbens, Sarah.  “Could a Parasitic Fungus Evolve to Control Humans? National Geographic.  January 19, 2023