Yes, the fungus that causes a zombie apocalypse in the hit HBO show "The Last of Us" does actually exist, but could the scenario in which it mutates to infect humans actually happen?
The new show has been making waves as its popularity has soared since its debut just a few weeks ago, but many have been left wondering if the premise behind it could come to fruition.
A fungus that takes over the brain of some insects mutates due to climate change, allowing it to survive in warmer conditions and ultimately spread to humans, turning them into "zombies."
Some experts say the possibility of a future fungal pandemic can't be ruled out, but they note that is quite unlikely.
"I think we're sort of at that inflection point where we don't ever dismiss anything as a possibility," Dr. Kamal Singh, chair of microbiology and virology at Cook County Health, told NBC Chicago. "I mean, who would have predicted SARS right? You know, we all had our eyes pretty much zoomed into things like, you know, hemorrhagic viruses, you know, ebola and avian flu and when's the next big flu pandemic coming ... and then all of a sudden we get hit by SARS. So I think no one discounts the possibility that it could be something else, and maybe that something else is a fungus. So the possibility is there, but then the question is, how probable is it? And I don't think it is as probable."
The fungus behind the zombie outbreak in "The Last of Us," known as cordyceps or ophiocordyceps, does in fact exist in the world already.
According to Harvard University, the spores of the fungus "infect a host, spreading the mycelium through the host’s body and digesting its internal organs."
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"After colonizing and killing the host from the inside out, the fungus produces a lengthy fruiting body that emerges to spread its spores to the next unsuspecting insect," the university's website states.
But the species of fungus has also been thought to having healing properties, as cordyceps have "been used in Traditional Chinese Medicine for centuries" with supplements derived from the fungus marketed to treat "a wide range of diseases."
Still, Singh noted that concerns have been raised surrounding fungi and changes seen in recent years.
"I think we definitely have our radar on the fungi. I can tell you that several years ago, it was less of a priority, but just last year, I want to say even the [World Health Organization] stepped up and said, 'You know what? We have to keep our eyes out on it,'" he said. "So they released a report in 2022 and said that, you know, we have a list of these fungi and and we should, you know, keep a lookout for them. ... So I I think there's much more attention being paid to the fungi."
The WHO report highlighted the "the first-ever list of fungal 'priority pathogens.'"
“Emerging from the shadows of the bacterial antimicrobial resistance pandemic, fungal infections are growing, and are ever more resistant to treatments, becoming a public health concern worldwide” Dr. Hanan Balkhy, WHO assistant director-general for antimicrobial resistance, said in a statement.
The list, however, did not name cordyceps among those of concern.
It's worth noting, however, that post-COVID fungal infections, though rare, have been reported during the pandemic, particularly in those with compromised immune systems.
"So it's very rare, but it has been described," Singh said. "And in essence, where we have seen it is in the very sick patients who have been treated with very heavy doses of immunosuppressive drugs."
The Centers for Disease Control and Prevention noted that "COVID-19-associated fungal infections can lead to severe illness and death."
"COVID-19 likely increases the risk for fungal infections because of its effect on the immune system and because treatments for COVID-19 (like steroids and other drugs) can weaken the body’s defenses against fungi," the CDC states.
But some fungal infections can also mirror COVID-19 symptoms, and one in particular is raising alarm as it spreads in the U.S.
And in another nod to "The Last of Us," climate change could be playing a role in its spread.
According to a recent study, "a fungal disease endemic to the southwestern United States" known for causing what is known as valley fever, is projected to spread east over the next several decades due to warming temperatures.
"By 2100 in a high warming scenario, our model predicts that the area of climate-limited endemicity will more than double, the number of affected states will increase from 12 to 17, and the number of Valley fever cases will increase by 50%," the study in the GeoHealth Journal reports. "The Valley fever endemic region will expand north into dry western states, including Idaho, Wyoming, Montana, Nebraska, South Dakota, and North Dakota."
“As the temperatures warm up, and the western half of the U.S. stays quite dry, our desert-like soils will kind of expand and these drier conditions could allow coccidioides to live in new places,” Morgan Gorris, who led the GeoHealth study while at the University of California, Irvine, and is now a staff scientist at the Los Alamos National Laboratory, told NBC News last month.
According to the CDC, the fungus that causes valley fever, Coccidioides, "lives in dust and soil in some areas in the southwestern United States, Mexico, and South America," including Arizona, California, Nevada, New Mexico, Texas and Utah. It was recently discovered in south-central Washington as well.
The most common way valley fever spreads is by inhaling spores from that particular fungus in the air. Symptoms can include fever, cough and shortness of breath -- mirroring those of COVID-19 or bacterial pneumonias.
The CDC notes, however, that the effects of climate change on the fungus' spread remains unclear.
"The ways in which climate change may be affecting the number of valley fever infections, as well as the geographic range of Coccidioides, isn’t known yet, but is a subject for further research," the agency stated.
Singh noted that testing for valley fever has also dramatically changed in recent years, though climate could also play a large role in its spread.
"Because this particular fungus is found in the soil, and as you know, they've had what's going on to nearly 10 years of a drought in California now, and so I think that creates the perfect conditions where dust gets blown up... when you have very dry conditions and the potential for these dust particles to get blown up with the fungus in it, you know there's a greater chance of getting infected," he said. "And so that I think that's another major thing."
He added that more travel could also lead to a spread in infections.
"There's definitely more movement of people and that is probably adding to the the number of infections that are being described outside of the typical zones where you see these," he said.
But when it comes to a future pandemic, Singh believes fungi likely won't lead the charge.
"I don't think it is as probable and part of the reason I say that is, if you look at something like, say, the SARS virus, it spreads very quickly because it has a very high reproductive rate. It is also spread through, you know, cough, nasal secretions, oral secretions... what we call the respiratory route, and that's a very efficient way of transmitting an organism," he said. "Whereas fungi are mainly found in soil and environments and that makes them less ideal for transmission... So I think that's what makes certain pathogens more efficient at causing epidemics and pandemics and the fungi just have never quite evolved to that extent. Now, could they... like in the case of this 'zombie ant' fungus, adapt to human body temperatures? I still think there are many other hurdles to overcome."
Chicago Department of Public Health Commissioner Dr. Allison Arwady also said she doesn't have a "high concern for a major fungal pandemic," adding that "a lot of things are heightened for TV in 'The Last of Us.'"
So what is more likely to cause another pandemic?
Experts say that remains to be seen, but preparations are already underway.
As for Singh, he fears something beyond viruses and bacterial infections.
"I will be honest with you that, you know, I worry about chemicals. I truly do," he said. "So not even things that are organic, more things that might be in the environment that could, you know, poison us. And there are many things, as you know, that people have to use chemicals that have, you know, in some form or another accidentally released or in the form of bioterrorism... that's something that we're all constantly afraid of. But if I'm really honest, in terms of a pathogenic organism, I still think most of the experts in the field more worry about viruses just because of the mutability, the speed at which they can reproduce, and this incredible shrinking of the space between animals and humans, the way we are traveling around so much, and the fact that, you know, we're all living in a very dense, urbanized kind of environment right now. And I think those are the kinds of environments in which, you know, a virus is more likely to lead to the next pandemic."
"Don't get me wrong, you know, we're highly respectful of the fungus," he added. "I'm a clinical microbiologist and I see patients regularly, you know, every week I have a patient who has a fungal infection. And so we're highly respectful of the role they play in human disease. But compared to the fungus, I see a hundredfold more viral and bacterial infections. So it's relative contribution to overall morbidity is much, much less. For now, in 2023. What will happen 10 years from now? I sure hope it doesn't become a reality though."
