Could Ophiocordyceps unilateralis really turn us all into zombies?
The risks of cordyceps causing zombieism in humans is extremely minimal, but it’s a fascinating idea. In some regions, some cordyceps are used as pesticides on crops – they’re using spores from those fungi because they’re good at killing caterpillars and ants and other pests, so maybe TV writers are imagining something going wrong in that scenario. But that’s not something we should be worried about.
What should we be worried about when it comes to fungi?
Right now, climate change is contributing to an increase in environmental fungi jumping into people. One of the main factors that seems to be leading to new and emerging fungal pathogens is rising planet temperatures. Our body temperatures, being 37 degrees Celsius, are our biggest protection against fungal infections – 95 percent of fungi can’t live at our body temperature. But these increasing temperatures in our atmosphere and oceans, and the increased frequency of extreme heat waves, is thought to now be selecting for fungi that can live at much higher temperatures.
One really important example that has been in the news quite a lot over the last 10 years is Candida auris. This is a yeast organism that is really good at sticking to people’s skin and people who have compromised immune systems or IVs can get disseminated infections. It’s resistant to almost every frontline anti-fungal and the concerning thing about auris is it didn’t really exist in people before about 2009. It emerged in long-term care facilities in 2009 and that’s when researchers named it, and several years later it emerged simultaneously in South Africa, parts of the U.S., and parts of Australia, and it’s not driven by any one strain. This is an environmental fungus that acquired the necessary traits to cause disease in humans and it’s really a problem.
Most people who get devastating fungal infections are immunocompromised, and that’s generally still true today. Untreated HIV is really where fungal pathogenesis took off, and unfortunately millions of people worldwide began getting life-threatening fungal infections. It’s one of the reasons there’s such a corollary between deadly fungal infections and lower-income countries, because rates of AIDS and HIV infection are much higher there. In the U.S. and other high-income countries, it’s the elderly and immunocompromised populations that are particularly susceptible to deadly fungal infection.
So, the impact that climate change has on fungi in “The Last of Us” isn’t that far-fetched?
Climate change, changing ecosystems, and global human movement are mixing populations of fungi that are not native to certain regions, and this has been associated with extinction events in certain animal populations. If you look at white-nose fungus, for example, this one is causing depletions or even just collapse of the brown bat populations in North America. It started causing infections in the early 2000s and what researchers think happened is this fungus was native to Europe and the bats there are resistant, but it migrated to North America and now a lot of different groups are trying to save bat populations.
A similar thing is happening with amphibians. About three decades ago scientists started noticing mass die-offs of frogs all over the world and discovered it was associated with a chytrid fungus. Now, about 100 frog species are extinct or presumed extinct.
It’s scary to have a situation where something like a fungus from the environment causes a deadly infection, because there’s no evolutionary advantage for that fungus to keep us alive. They don’t depend on us for a host, so what that means is these fungi can actually drive extinction events. It’s happening in some animals because there’s no evolutionary pressure to keep whatever they’re killing alive.
Another problem associated with climate change is the expanding habitat of fungi that are known to cause disease. There’s a fungus that lives in soil in the American southwest called Coccidioides that causes infections in humans – it’s usually called Joaquin Valley fever or valley fever – when they inhale the spores. It can cause really serious, long-term infections, and the habitat for that fungus in the soil is expanding. It’s found in hot, arid climates, but as the planet warms and we’re seeing greater rates of desertification, the range of where that fungus can live is expanding. It’s now been found in Colorado.
Is a popular show like “The Last of Us” helpful in making people aware of what’s happening with fungi in relation to climate change?
The mycology research community is definitely stoked about “The Last of Us.” I think a lot of it is driven by awareness and education. It might be more convenient to ignore fungi because when they’re emerging from our changing environments, it’s not like that can be controlled with masks or social distancing. And while it’s very uncommon that they’re spread human-to-human, we have a lot of catching up to do in learning about risk and spread, and in developing effective treatments.
I do think the public’s awareness and knowledge of all the ways we’re being impacted by climate change is growing, but we’re just not being introduced to the importance of environmental fungi early enough or to the degree that we should. It’s something that I and a lot of researchers are trying to convince students of, that it’s a very exciting time to be in this field.