Learn About Cordyceps Niels-Viggo Hobbs, a researcher at the URI, talks about the parasitic fungus at the heart of HBO’s sci-fi series, The Last Of Us.

Learn About Cordyceps

You’ve probably heard of Learn About Cordyceps if you’re a fan of HBO’s post-apocalyptic series “The Last of Us” or the video game that inspired it. In the show, the parasitic growth has changed, moving on from contaminating bugs to people – changing them into mind-controlled zombies. Yet, it’s not all sci-fi.

The real Learn About Cordyceps, officially known as Ophiocordyceps unilateralis, may have been unfairly made the bad guy for the sake of entertainment. What’s more, there is a genuine and interesting story behind them, less the incredible storyline. 

Niels-Viggo Hobbs, Ph.D., ’16, an assistant professor of biological sciences at the University of Rhode Island, lends his expertise to carefully guide us through the world of Cordyceps. He has been a lifelong fan of science fiction, horror films, and “weird fiction” literature. He also enjoys the HBO show and is a researcher of invasive species and teaches a parasitology course.

What is Cordyceps? Where can you find the fungus? It infects what kinds of hosts? And why not people?

A type of parasitic fungus known as Learn About Cordyceps has a remarkable, one-of-a-kind, and quite troubling method of infecting its host, typically ants.

Although the genus Cordyceps is the most common name for this parasite, there are actually hundreds of species of fungi in at least two different taxonomic families that can be found all over the world, most often in the tropics, and all of them live similar lifestyles to endoparasitoids. This indicates that they infect a host, typically an insect, and grow within it until they literally burst out, killing the host, frequently in a dramatic way.

Funny enough, despite the fact that these parasites do not appear to have any ability to infect humans or other vertebrates, we frequently contain these fungi in our bodies. In fact, in Chinese traditional medicine, they are frequently taken involuntarily, and there is some evidence to suggest that they have some medicinal value. However, these are not the active, infectious organism; rather, they are powdered, dried forms of the fruiting body, which we would call a mushroom.

What causes Cordyceps to take over its host and how does it do so? How does it grow?

The basic premise is that the adult organism’s fruiting bodies, or ascocarp, release extremely small spores that are inhaled or otherwise penetrate the potential host, such as an insect. There is, of course, some variation between species. After that, the spores mature into fungal tissue, which begins to spread throughout the insect’s body and begin to slowly consume it from the inside out. But even that isn’t the best or worst part. The fungus is prepared to move on to the next phase at some point: reproduction.

This is where it really gets interesting. The host is transformed into a fungus-driven zombie as the fungus begins to take control. Also, this is something that many parasites and parasitoids are shockingly good at, but this organism does it really well.

The insect is now forced to climb the nearest tree or tall structure by the fungus. When the insect-fungus zombie reaches a height that is high enough, the insect really latches on, and the fungus starts to come out with its reproductive fruiting body.

These appear to be tiny, dramatic finger-like projections and break right through the insect’s body wall. At this point, the insect host has already passed away, so the poor thing doesn’t feel any pain. The life cycle is completed when the fruiting bodies release clouds of very fine spores that drift down on everything below, including potential insect hosts. Living this way is very cool and grizzly.

How does Cordyceps influence insect behavior?

Although the specific metabolic and chemical means by which these fungi hijack their host’s central nervous system are still poorly understood and probably differ slightly between the various species of these parasites, it appears that they release chemicals that elicit basic motor-neuron responses in their hosts. For example, in the case of some infected ants, they force them to latch onto the limb of a high tree with a literal death grip of a bite, immobilizing the jaws to prevent the host from falling off the

Again, this general ability to hijack a host’s behavior is extremely common across all parasite and parasitoid groups of life. An example of this is the extremely straightforward single-celled parasite Toxoplasma gondii, which infects rodents and causes them to do extremely stupid things, most notably to lose all concern for their top predator, which is also the parasite’s ultimate host and goal: cats in homes!

Does this behavior occur frequently in any other fungi?

Numerous parasitic fungi exist. In fact, some of the most common ways that life on this planet survives are parasitism and parasitoidism, in which the host is killed to complete the parasite’s life cycle.

Many of the thousands of bacteria and protist species that make up our own body’s microbiomes are parasitic. While there are many parasites that are capable of influencing the behaviors of their hosts, very few of them do so in such a dramatic way.

However, the common name Cordyceps is used to refer to hundreds of different species of fungi, so there is no shortage of these organisms. And since they are distributed worldwide, they are truly everywhere.

What aspects of Cordyceps have “The Last of Us” gotten right and wrong?

They really get a lot of things right, especially when it comes to manipulating the host and completely destroying the host body at the end of the parasite’s life cycle.

However, there are certain fundamental flaws in their approach. First and foremost, the fungus does not appear to be capable of hive-mind communication as depicted in the show. The fact that they completely skip the dispersal of spores, which completes the primary infection of the host, is the most notable and unfortunate aspect for me.

Obviously, the main way they might have all the more fittingly shown this was to have everybody wear very much fixed veils (which, as a matter of fact, may not be sufficient to safeguard us), and I don’t figure Pedro Pascal would need to be in yet-another show where he’s essentially wearing a cover.

Interestingly, the non-infected humans in the original video game that this show is based on do wear masks to prevent infection. Since it is both more accurate and far more terrifying, I honestly wish they had kept this for the show. Instead, they have this weird, disgusting French kiss that spreads. Not as cool as before.

Is mutation, the show’s premise, really that far-fetched?

It is a major stretch to have people being the parasitized, commandeered, and obliterated have creature since Cordyceps don’t the slightest bit contaminate people. Be that as it may, the general reason isn’t somewhat fantastical. Obviously, it is science fiction, which is fortunate. The fact that there is a solid foundation in reality and biology that we can actually see happen in our remarkably non-fictional natural world is, for me, the part that makes it the most exciting and terrifying.

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Tony LaRoche