The wait was long for the fans but it is coming to an end: the release of season 2 of the post-apocalyptic American series “The Last of Us” is scheduled for April 14, 2025. This series was acclaimed by the public as by critics and received several prizes. It is the adaptation of a homonymous video game released in 2013 which has sold several tens of millions of copies itself. The synopsis is effective and particularly original: since 2003, humanity has been plagued by a pandemic caused by a fungus called Cordyceses. The latter is able to transform “infected” into aggressive zombies and has led to the collapse of civilization. The survivors organize as best they can in a violent environment in quarantine areas controlled by a military organization, the Fedra. Rebel groups such as “fireflies” fight against this authoritarian regime.
Zombified insects
Developers Neil Druckmann and Bruce Staley say that the idea of video games was born following the viewing of an episode of the documentary series Planet broadcast on the BBC channel.
This very impressive episode shows how the fungus Ophiocordyce unilateralis Who has infected an ant takes control of its host by acting on muscles control to bring it to a place in height particularly conducive to the dissemination of mycy to other ants.
Some speak of zombie ants and a fungus that plays the role of puppeteer. Once in height, the ant plants its mandibles in a rod or a leaf and awaits death.
Surprisingly, healthy ants are able to recognize an infection and hasten to transport the infected fellow as far as possible from the colony. Here is the reason: the fungus present inside the insect will pierce its cuticle and form a fruiting (a sporophore) allowing the spread of spores (the seed equivalent) outside. These spores produced in large quantities are the cause of new infections when they meet a new host.
Although spectacular, it is not the only “behavioral manipulation” known to a host by a fungus. We can cite cases of control of the flies or cicadas, so that the insect becomes a mobile vector to widely and effectively disseminate fungal spores in the environment. The molecular mechanisms which support control of the behavior of ants begin only to be pierced, they are complex and seem to involve a cocktail of toxins and enzymes.
The good news is that the scenario of a host of the insect to man is not very credible, even if this phenomenon is quite common in mushrooms. This is the case with fungal organisms initially parasites of arthropods which ultimately specialized as parasites of other fungi.
The main reason is that expansion to a new host preferentially concerns an organization close to the primary host. It is clear in our case that humans and insects do not constitute close phylogenetic taxa. There are also major physiological differences, if only the complexity of the immune system or body temperature, which constitute an undoubtedly insurmountable obstacle for an adaptation of the ophiocordycept mushroom. Another factor favoring successful host jumps concerns a coexistence area by habitat preferences that overlap at least partially. Here again, we can estimate that insects and humans do not repeated and brought the same ecological micro-niches in a repeated and close-up, which dismisses the hypothesis of a leap from Ophiocordycepts to humans.
Real threats to humans
Once dismissed the imminent threat of massive zombification, the fact remains that fungal infections have been identified by scientists as an increasingly worrying danger. In recent decades, an increasing number of infectious diseases of fungal origin has been identified whether in animals or in cultivated and wild plants.
The concern is such that Sarah Gurr, plant pathologist at the University of Oxford, co-signed a comment in the journal Nature in 2023 which is a warning. It warns against the “devastating” impact that fungal diseases of cultures will have on global food supply if agencies around the world do not unite to find new ways to fight infection. At the planet's scale, the losses caused by fungal infections are estimated each year between 10 and 23 % of the harvests, despite the widespread use of antifungals. For five crops providing substantial calorie intake, namely rice, wheat, corn, soybeans and potatoes, infections cause losses that are equivalent to a sufficient amount of food to provide 2,000 calories per day of some 600 million to 4 billion people for a year. Food security is therefore preparing to deal with unprecedented challenges because the increase in population results in an increase in demand.
The devastating impact of fungal diseases on crops should also worsen in the coming years due to a combination of factors. First of all, climate change is accompanied by a regular migration from fungal infections to the poles, which means that more countries are likely to experience a higher prevalence of fungal infections damaging crops.
This phenomenon could, for example, be the source of the identification of black wheat rust symptoms in Ireland in 2020. This disease exclusively affects the aerial parts of the plant, producing external pustules and disturbing in particular nutrition. It is the source of substantial loss of yields, which can go up to 100 % in cases of infection by particularly virulent isolates.
Then, the generalization in agriculture of monoculture practices, which involve large areas of genetically uniform cultures, constitutes ideal breeding grounds for the rapid emergence of new fungal variants. Let us not forget that mushrooms are organizations that evolve quickly and which are extremely adaptable. Added to this is that fungi are incredibly resistant, remaining viable in the ground for several years, that spores can travel around the world, especially thanks to increasingly intense trade. A final point far from negligible is that pathogenic fungi continue to develop resistance to conventional fungicides.
Risks to human health
The impact of fungi on human health also tends to be underestimated, although these pathogens infect billions of people worldwide and kill more than 1.5 million per year.
Some recent events particularly concern scientists. This is the case with Candida Auris which would be the first human fungal pathogen to emerge due to thermal adaptation in response to climate change. This yeast constitutes a new major threat to human health because of its ability to persist, in particular, in hospitals and its high level of antifungal resistance. Since the first case reported in 2009 in Japan, infections to C. Auris have been reported in more than 40 countries, with mortality rates between 30 and 60 %. The majority of these infections occur in seriously ill patients in intensive care units.
The alarming increase in the number of Azols resistant pathogens is another source of concern. Azols are widely used in agriculture as fungicides, but they are also used in therapeutics to treat fungal infections in humans and animals. Their double use in agriculture and clinic has led to the global emergence of resistance to Azols, especially in C. Auris but also in mushrooms like Aspergillus. These have long been considered major human pathogens, with more than 300,000 patients developing this infection each year.
The numerous emergences and the identification of the resistance to antifungals in multiple pathogenic fungi provide weight elements to the defenders of the concept “One Health”, which recommend that human, plant and animal health are considered to be closely interconnected. These researchers from prestigious universities offer updated recommendations to meet scientific and public health challenges in this changing environment.
