(CNN Spanish) — The video game and the subsequent series “The Last of Us” have its users wondering if 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 Cordyceps fungus 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.
Dr. Huerta explains the details to us in this episode. The office is open, welcome!
You can listen to this episode 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 en Español. Dr. Huerta greets you, I hope you are well.
“Zombie mushrooms”: 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 could 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 of them. They try to bite other people to transmit the infection to them.
The interesting thing about the series, and the reason for making this episode a science and medicine podcast, is that the fungus in question —called cordyceps— it is real.
It has long been known that it is capable of infecting various species of insects. It has been shown that this fungus changes its behavior after growing inside them, which is why they were dubbed “zombie mushrooms”.
We must clarify that experts agree that infections by these fungi have not been recorded in humans. It is very unlikely that this will happen due to the enormous difference between the structure of the human being and that of insects.
However, it is interesting to examine the mechanism by which fungi change the behavior of insects, because some chemicals in the fungus could have applications in medicine.
what are mushrooms Cordyceps?
mushrooms Cordyceps They 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 become infected through fungal spores found in the environment, which grow within their bodies over a period of 24 to 48 hours and that in two or three weeks they spread within it.
In accordance with rebecca rosengausan associate professor of marine sciences and environmental sciences at Northeastern University, the fungus produces neurotoxins, or neuromodulators, that change the neurobiology of the insect, essentially turning it into a zombie organism.
Similarly entomologist David Hughes, who worked as a consultant on the game “The Last of Us,” says the fungus surrounds the insect’s muscles, affecting its motor neurons, turning it into a puppet.
The effect of those fungi on ants
This change in the behavior of the ant is extraordinarily surprising, because at a certain moment of the infection, the zombie ant looks for a branch that is exactly at 25 centimeters of an ant colony. Upon reaching that point, which is supposed to have the most propitious temperature and humidity for the development of the fungus, the ant sticks its jaws into the vein of the leaf and anchors itself in that place, later observing a shocking scene It sounds like science fiction.
Little by little, from the ant’s head, the fungus begins to emerge. Cordyceps. A kind of worm with a dilated end like a fruit full of seeds is visible. From there come thousands of spores that fall on the ant colony located below the dead ant to infect them, or that are carried by the wind to infect other distant colonies.
The intelligence of the ants is such that the workers are constantly watching for the presence of zombie ants. The “zombies” are recognized because -when they are infected- they acquire an antisocial behavior, completely different from that of the other members of the colony. 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. Having seen, as we have said, that fungi contain various chemical compoundsincluding nucleosides, cyclic peptides, sterols, flavonoids, alkaloids and various polysaccharides, through which they would exert their effects on the infected insect.
One of those substances present in the zombie fungus, the 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 magazine molecules As of September 2021, UK researchers do 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:
- Tumor growth reduction in 37 articles,
- Decreased 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 since 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; however, 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 replication inhibition of the virus, such as a probable protective effect of the brain and lungs during covid-19.
The fact that a chemical substance, derived from such a strange zombie fungus, can be useful to humans should not attract attention.
Let us remember that the psilocybin and the LSD – hallucinogenic substances that have been extensively studied in recent years to treat depression and other mental health disorders – are chemicals derived from mushrooms. Similarly, the antibiotic penicillindiscovered by chance by the Scottish bacteriologist Alexander Fleming in 1928, is also a by-product of a fungus, the penicillium notatum.
What other factors change behavior in 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 intestine of cats has strange properties when it infects mice.
Apparently the mouse infected with Toxoplasma he develops brain lesions that completely change his behavior. This occurs through an inflammatory mechanism, although it is also possible that it is through chemical substances or an immunological reaction.
Normally, mice are very cautious, careful and fearful animals that flee from certain environments and smells that may indicate a danger to their integrity.
But surprisingly, mice infected with Toxoplasma they 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 thought that this change in the behavior of the mice would be intended for the Toxoplasma It can infect other animals, especially cats, animals in whose intestines it reproduces.
It is precisely because of these types of observations that it has been postulated that schizophrenia would be related to infection by the Toxoplasma .
The Toxoplasma and schizophrenia… is there a relationship?
even though there is more than 100 studies that associate infection with Toxoplasma 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 complex to show that infection by Toxoplasma preceded the diagnosis of schizophrenia.
However, a study published in 2019, in more than 80,000 blood donors in Denmark, has found that the risk of developing schizophrenia was 2.7 times higher in people who were infected before the onset of the disease.
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 body, especially in pregnant womenin whom it can cause premature labor and cause blindness and mental retardation in babies.
Prevention consists of having our cats examined periodically, especially if we allow them to go outside the house. Cats get it Toxoplasma by eating contaminated food outside the home.
In summary, with the cinematographic license to eliminate from the script the scientific fact that the fungus is spread through spores (they have changed it to bites), the series “The Last of Us” has some real scientific elements, which we They make us reflect on the delicate and often unknown balance between the living beings that inhabit the planet.
Do you have questions for Dr. Huerta?
Send me your questions on Twitter, we will try to answer them in our next episodes. you can find me at @DrHuerta.
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