Newsroom
The Last of Us Season 2: A Q&A with Dr. Jim Kronstad about fungal infections and climate change
The Last of Us is back on April 13 and this season is more realistic than ever.
The trailer for the hit HBO series appears to show the “zombie fungus” cordyceps infecting humans by releasing air-borne spores, instead of through tentacles – closer to scientific reality.
Indeed, many fungal diseases than infect humans, such as Cryptococcus neoformans, which causes meningitis in humans, are spread by inhaling spores.
It’s not the only thing the show gets right. In The Last of Us, cordyceps – which is harmless, even edible, in real life – evolved into a harmful fungus thanks to a warming climate.
In a recent Nature paper, Dr. Jim Kronstad (MSL, Microbiology and Immunology, Land and Food Systems) and co-authors highlight a warming climate as a potential contributor to the spread of harmful fungi. However, fungi aren’t all bad.
“Fungi are super important, it’s phenomenal what they’ve done for humans,” says Dr. Kronstad.
We spoke with Dr. Kronstad to learn more about the science behind fungi, accuracies and inaccuracies of the science of the TV show, and what we can expect from fungi with a warming climate.
Petri plates containing colonies of the fungal pathogens Ustilago maydis and Cryptococcus neoformans, random fungal colonies from air sampling, and the orange fungus Neurospora crassa. Credit: Alex Walls, UBC Media Relations
Cordyceps is the fungus that causes disease in The Last of Us. What is cordyceps?
Cordyceps is a genus of fungi that generally infect insects. When people talk about the science behind The Last of Us, the example often referred to is how some species of cordyceps infect ants, colonize their brains, and affect behaviour because of chemicals released during infection. This leads to ants climbing somewhere higher up, like tree branches, before the fungus produces spores to rain down on other ants to start the infection cycle over again. In this case, cordyceps forces a behavioural change in its host to spread itself.
In the first season of the show, people were infected from coming in contact with fungal ‘tendrils’. Does this happen with real life fungi?
I saw that episode when they were breaking out of the soil and breaking up the road with their giant tendrils. That phenomenon doesn’t occur that dramatically, and not with human pathogens. Fungi that form mushrooms are abundant in the soil – in fact, 90% of all trees have fungi colonizing their roots. Sometimes, the collections of filaments of mushroom-forming fungi can come up through the ground, with some even powerful enough to push through asphalt. These tendrils, however, are not the main way fungi infect humans.
What would a more realistic model for human infection look like? The show is introducing ‘spores’ this season, pulling from the video game the show is based on.
Fungi love to make spores, and some human infections that occur are because we’re inhaling spores from the environment. This is a common way that fungi spread, not only for human pathogens, but most commonly for fungal pathogens of plants, so spores are a more realistic model for the show to use.
Scanning Electron Microscope (SEM) image of Cryptococcus neoformans. Credit: Kabir Bhalla, Kronstad Lab
The fungus that my lab studies, Cryptococcus neoformans, is an example of one that is inhaled. While generally this doesn’t lead to disease in healthy people, it can cause meningitis in individuals who are immunocompromised. For example, these infections are very common in people with HIV/AIDS, with an estimated 19% of deaths from HIV/AIDS being caused by C. neoformans.
Another pathogenic fungus, Aspergillus fumigatus, is also a threat to immunocompromised people, and this fungus is commonly found in the environment and produces abundant spores. However, two other pathogenic fungi of concern, Candida auris and Candida albicans, are more often found on our skin and in our intestinal tract as opposed to being inhaled, and can usually only cause disease when there is a change in immune status.
Can fungi cause behavioral changes in infected humans?
No, not in the same way it’s presented in the show. When C. neoformans causes meningitis, it can affect things like eyesight, hearing or movement, but this is a symptom of damage to the brain rather than a chemical leading to a change in behaviour.
Is there a concern with climate change that we will see new fungal pathogens evolve to infect humans?
I think there is definitely a concern, as an important way that we keep fungi in check is because most of them can’t grow at our high body temperatures. Increasing global temperatures offers an opportunity for fungi to adapt, as they have pretty fast generation times and mutations may occur that help them survive at higher temperatures.
In the show, one of the characters is immune to cordyceps – is this possible, either naturally or through vaccination?
That immunity side of things is a little tricky when it comes to fungal pathogens. Of course, our body temperature keeps most fungi in check, but it is also possible to vaccinate people against pathogenic fungi. There are promising vaccines against three fungal pathogens, but these haven’t been commercialized yet. They are, however, a realistic possibility.
Should we be concerned about fungi?
While climate change could potentially lead to new fungal threats, I think there are other aspects of a warming climate that are of greater concern. For fungi, I think there are so many more positive things out there to appreciate because of the benefits they provide.
The biggest one is that they act as significant carbon sinks, as the fungi that colonize 90% of land plants store carbon that would otherwise end up in the atmosphere. We would also be buried in leaf litter if not for fungi that help to break organic matter down into our soil.
Fungi have a great diversity of activities, many of which we are dependent on, and they also hold potential to help tackle global challenges across the fields of food production, sustainability, technology and more.
This story builds off of a news tip posted by UBC News.
Media stories: