Chicago's Top Doctor Offers ‘Deep Dive' Into Fungus at Center of Zombie Apocalypse in ‘The Last of Us'

Chicago's top doctor took a "deep dive" into the fungus behind the zombie apocalypse in the hit HBO show "The Last of Us" this week, noting that the fungus is actually real and does have a "mind control concept."

Dr. Allison Arwady, the commissioner for the city's health department, said that "public health pays attention to fungal infections and fungal outbreaks," but echoed other experts who say "it is quite unlikely that a fungus would cause a global outbreak."

"We remain much more concerned about viruses like COVID, like influenza," she said during a Facebook Live Tuesday.

Even still, she noted that the Centers for Disease Control and Prevention has previously done drills, particularly following the popularity of other zombie-related shows like "The Walking Dead."

The doctor, who said she has worked on fungal outbreaks before, said she took a deeper dive into the newest apocalyptic show and how the hypothetical fungal pandemic happens.

"It is based on an actual fungus. Cordyceps is the family," Arwady said. "And yes, this is an actual fungus. It can infect and kill insects. There's about 400 different species of this cordyceps fungi, and each of those species has evolved to better target a different species of insect. So species of various ants and beetles and flies and spiders, but insects."

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."

"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 Arwady notes that there's also a mind control element to it.

"So for those of you who follow zombie movies, there tends to be this idea of infection taking over the mind. And the reason that the writers chose cordyceps is that cordyceps do sort of control the insect's brain," she said. "So let's talk about that. Once inside the insect body, the spores sprout these long tendrils kind of mycelium, they're called. And scientists aren't entirely sure how this works. So either there are fungal spores that eventually reach into the brain or they're releasing chemicals. Maybe there's some physical manipulation of muscle fibers from these chemicals. They're not entirely sure, it turns out. But the chemicals or this other manipulation from the fungus, it actually compels the insect to move. It makes this infected insect move to the favorable location where the fungus can thrive and grow. So usually it'll make the beetle or the ant or whatever climb high to where the wind can pick up the fungal spores before expelling it for its spores. The fungus then keeps eating the insect and sprouting new spores. The spores burst and release more spores into the air and in fact, more hosts. So it's this really unusual cycle."

In "The Last of Us," the fungus mutates due to climate change, allowing it to survive in warmer conditions and ultimately spread to humans, turning them into "zombies."

But Arwady said that's not likely to happen.

"This fungus cannot infect humans," she said. "First of all, our body temperatures are high enough that the proteins would denature. Really, it's not going to survive. And this fungus has evolved over millennia to attack insects in very specific ways, like through the exoskeleton, which we don't have. And you know, you can think about climate change, it's right to sort of be aware, but yes, there are fungal species that are also known to alter a human's mental processing. The best known is probably psilocybin or magic mushrooms. Those are fungi that that humans are known to ingest and that will affect their their mental processing, but not in a controlling them kind of way."

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."

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.

Arwady said it remains something the city is monitoring.

"As we're seeing some climate change and we're seeing fungi and mosquitoes and other changes," she said. "You know, there's certainly something to keep an eye on, but we have folks at the Chicago Department of Public Health and the Illinois Department of Public Health who know this, who follow up when there are cases, who work to investigate and to make sure we're not seeing more spread."

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."

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."