Joy Bromley
I don’t know about you but the The Last of Us keeps cropping up in my life, be it my lecturer or the exercise instructor, this massive new HBO series seems to be hitting people close to home. Having largely recovered from the global Covid-19 pandemic our attention is turning to what is to come next. Could it be an influenza pandemic, as some people predict, or could it be something new… like a zombie causing fungus?
The Last of Us sees survivors fighting for life in a post-apocalyptic world. The fungal infected are mind-controlled zombies impulsively intent on biting the uninfected to spread the disease further, while the remaining uninfected people struggle to rebuild a functioning society. Although this makes a brilliant TV show, there are surprising parallels between this fungus and real-world species, leading us to question if this could really happen.
The message is that if a fungus like this was able to adapt to infect humans, it would be a major threat
The species described in the show is comparable to Ophiocordyceps genus of fungi which can infect a range of invertebrates, turning them into ‘zombies’. Once a suitable host is infected, the fungus will grow within the living animal, slowly digesting it from the inside, and releasing compounds which controls their brain. The infected insect, such as a bullet ant, then starts to act in ways very out of character, including deserting its roles in the colony and climbing up to higher places in the canopy. Once there, an infected ant will latch onto a branch and die as the fungus fruiting body grows out of the remains, thus maximising the opportunity for the infectious fungal spores to disperse to a new host.
Upon spotting signs of infection in a fellow ant, a colony will remove and isolate that ant in an attempt to limit the spread of the disease, much in the same way that humans would isolate infected individuals. In The Last of Us’ pandemic, governments took these control measures to drastic extremes including the bombing of major cities, all to little benefit. The message is that if a fungus like this was able to adapt to infect humans, it would be a major threat.
Luckily, however, we don’t need to begin prepping for a zombie apocalypse just yet. Firstly, in order to infect a human, the fungus would need to adapt to be able to grow at the warmer body temperature. ‘But global warming!’ I hear you cry. It is very unlikely that the fungus would be able to evolve fast enough to transmit to such a drastically different host before its host species went extinct as a result of climate change.
Only last year the World Health Organisation published a list of priority fungal pathogens
Furthermore, each cordyceps fungal species has just one specific host, suggesting host and fungal parasite have co-evolved over millennia and thus are uniquely adapted to each other. There are also relatively few invasive fungal pathogens of humans in the world full stop, especially when compared with the number of deadly bacterial and viral infections, and most of them only cause disease in individuals with pre-weakened immune systems.
When considering fungal infections that aren’t zombie-causing, however, climate change might have a role to play in increasing risk, alongside the emerging threat of drug resistant fungi. It was only last year that the World Health Organisation published a list of priority fungal pathogens, with 11 species listed as being ‘critical’ or ‘high’ priority for research based on the threat that they pose to human health. Further to this, a fungal species Coccidioides immitis has been declared a bioterrorism risk. So, zombies maybe not, but future threat from a fungal pathogen there could well be.
Joy Bromley
Featured image courtesy of Ali Bakhtiari via Unsplash. Image license found here. No changes were made to this image.
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