Can ‘zombie’ fungus Cordyceps from The Last of Us infect humans? science explains

The video game and series “The Last of Us” instigated the question whether such a situation could occur in real life.

In the series, which airs on HBO Max – part of Warner Bros. Discovery, our parent company – the fungus Cordyceps it is transmitted from human to human through a bite, turning its host into a fast and aggressive zombie. In real life, the fungus only affects insects.

doctor Huerta explains the details in this episode. The office is open, welcome!

You can listen to this episode in Spanish on Spotify or your favorite podcast platform, or read the transcript below.

Hello, welcome to this new episode of In Consultation with Dr. Elmer Huerta, your favorite health podcast on CNN in Spanish. doctor Huerta greets you, I hope you are well.

“Zombie fungi”: from the real world to science fiction

In today’s episode, we are going to examine some scientific aspects related to the so-called “zombie fungi” and other microorganisms that have the ability to change the behavior of the hosts they infect.

If you are a fan of television series, you may have recently paid attention to a series called “The Last of Us”, which can be loosely translated as “The Last of Us”.

The nine-episode series on the HBO Max platform is the film adaptation of an electronic game of the same name created in 2013. The production describes life in an apocalyptic world in which humanity was almost exterminated after a pandemic caused by a fungus.

In the series, people infected by the fungus are transformed into a kind of aggressive zombie in which the fungus grows inside them. They try to bite other people to pass the infection on.

What’s interesting about the series, and the reason for making this episode a science and medicine podcast, is that the fungus in question – called Cordyceps – is real.

What is Cordyceps and what actually causes the zombie fungus mentioned in “The Last of Us”?

It has long been known that it is capable of infecting several species of insects. This fungus has been shown to change its behavior after growing inside them, which is why they have been nicknamed “zombie fungi”.

We should clarify that experts agree that infections by these fungi have not been recorded in humans. This is very unlikely to happen due to the huge difference between the structure of humans and insects.

However, it is interesting to examine the mechanism by which fungi alter insect behavior, because some fungus chemicals may have applications in medicine.

What are cordyceps fungi?

Cordyceps fungi constitute a family of dozens of species that are consumed by some Asian cultures as food and have been extensively studied due to the type of infection they cause in carpenter ants.

Ants are infected by fungal spores found in the environment, which grow inside their body within 24 to 48 hours and spread within two to three weeks.

According to Rebeca Rosengaus, an associate professor of marine and environmental sciences at Northeastern University, the fungus produces neurotoxins, or neuromodulators, that alter the insect’s neurobiology, essentially turning it into a zombie organism.

Likewise, entomologist David Hughes, who worked as a consultant on the game “The Last of Us”, says that the fungus involves the insect’s muscles, affecting its motor neurons, turning it into a puppet.

The effect of these fungi on ants

This change in the ant’s behavior is extraordinarily surprising, because at a certain point in the infection, the zombie ant looks for a branch that is exactly 25 centimeters from an anthill. Upon reaching that point, which is supposedly the most favorable temperature and humidity for the development of the fungus, the ant thrusts its jaw into the vein of the leaf and anchors itself in that spot, later observing a shocking scene that seems to be from science fiction.

Gradually, from the ant’s head, the Cordyceps fungus begins to emerge. You can see a kind of worm with a dilated tip like a fruit full of seeds. From there, thousands of spores come out that fall on the anthill located below the dead ant to infect it, or that are carried by the wind to infect other distant anthills.

The intelligence of ants is such that workers are constantly on the lookout for zombie ants. The “zombies” are recognized because – when they are infected – they acquire an antisocial behavior, completely different from the other members of the colony. Upon recognizing them, the workers drag the infected ants away from the colonies to die there and thus avoid infection.

This natural event is perfectly documented and studied. Since, as we said, fungi contain various chemical compounds, including nucleosides, cyclic peptides, sterols, flavonoids, alkaloids and various polysaccharides, through which they would exert their effects on the infected insect.

One of these substances present in the zombie fungus, cordycepin —which is chemically a nucleoside analogue— is being studied in the laboratory to determine its use in human medicine.

Cordycepin and use in humans

In this regard, in a study published in the journal Molecules in September 2021, UK researchers conducted an extensive review of the medical literature on the properties of cordycepin.

After identifying 1,204 publications, the researchers determined that 791 were of sufficient quality to be considered in the review. In 150 animal studies, they determined that cordycepin demonstrated some potential therapeutic effects. These include:

• Reduction of tumor growth in 37 articles,
• decrease in pain and inflammation in 9 articles,
• protection of brain function in 11 articles,
• improvement of respiratory and cardiac function in 8 and 19 articles, respectively,
• and improvement of metabolic disorders in 8 articles.

The authors conclude that, as the mechanism of action of cordycepin and the way in which this substance is distributed in the body are unknown, it is still premature to be optimistic, but it deserves further investigation.

By the way, during the pandemic, cordycepin was studied as a possible treatment against SARS-CoV-2, both for its properties of inhibiting the replication of the virus, and for a probable protective effect on the brain and lungs during Covid-19 .

The fact that a chemical, derived from such a strange zombie fungus, could be useful to humans shouldn’t draw attention.

Remember that psilocybin and LSD – hallucinogenic substances widely studied in recent years to treat depression and other mental disorders – are chemical substances derived from mushrooms. Likewise, the antibiotic penicillin, discovered by chance by the Scottish bacteriologist Alexander Fleming in 1928, is also a by-product of a fungus, Penicillium notatum.

What other factors alter the behavior of animals?

But fungi are not the only microorganisms that cause behavioral changes in animals.

It has long been known that the parasite toxoplasma gondiiwhich reproduces in the intestines of cats, has strange properties when it infects mice.

Apparently, mice infected with Toxoplasma develop brain lesions that completely change their behavior. This occurs through an inflammatory mechanism, although it is also possible that it is due to chemical substances or an immune reaction.

Normally, rats are very cautious, careful and fearful animals that flee from certain environments and smells that could indicate danger to their integrity.

But surprisingly, mice infected with Toxoplasma lose that fear and become very curious. They lose their fear and are exposed not only to cats, but to many other animals that eat them.

It is believed that this change in the mice’s behavior would have the purpose of allowing Toxoplasma to infect other animals, mainly cats, animals in whose intestines it reproduces.

It is precisely because of these types of observations that it was postulated that schizophrenia would be related to infection by Toxoplasma.

Toxoplasma and schizophrenia… is there a relationship?

Although there are more than 100 studies linking Toxoplasma infection with schizophrenia, due to the rarity of this disease, it is very difficult to study this correlation and conclude that there is a cause and effect relationship.

This is especially difficult because it is difficult to prove that Toxoplasma infection preceded the diagnosis of schizophrenia.

However, a study published in 2019, in more than 80,000 blood donors in Denmark, found that the risk of developing schizophrenia was 2.7 times higher in people infected before the onset of the illness.

Although the relationship between toxoplasmosis and schizophrenia is still not definitively clear, human toxoplasmosis is a real disease, capable of producing multiple complications in the organism, mainly in pregnant women, in which it can cause premature birth and blindness and mental retardation in babies.

Prevention consists of periodically examining our cats, especially if we allow them to leave the house. Cats get Toxoplasma by eating contaminated food outside.

In summary, with the cinematic license to eliminate from the script the scientific fact that the fungus is spread by spores (they changed it to bites), “The Last of Us” series has some real scientific elements, which make us reflect on the balance delicate and often unknown among the living beings that inhabit the planet.