The deadly rise of fungal spores

It sounds like something from a Pedro Pascal zombie drama, but the rise of deadly fungal spores has got some in the scientific community running scared.

Neither plants nor animals, fungi are “the most populous life form” on Earth, with an estimated 12 million species ranging from edible mushrooms to fungal parasites, said The Guardian’s science correspondent Linda Geddes. And at their most aggressive, fungi can take over a host’s body and mind in order to further spread their spores.

What are fungal spores?

Released from a fungus’s reproductive structures, otherwise known as fruiting bodies, “spores carry instructions for a future shiitake, puffball, bread mould, plant rust, or brain pathogen”, said Emily Monosson, author of “Blight: Fungi and the Coming Pandemic”, in Time magazine.

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Whether carried “in the air, between the toes of a bird, or in the crevasses of our shoes”, spores are the form in which fungi travel across continents and oceans.

Atmospheric chemists estimate that around 50 million tonnes of spores populate the planet’s atmosphere annually. “With every breath we take, we suck in tens, or thousands or millions of spores, many of which have been ejected, squirted, blasted, or simply dropped from dozens if not hundreds of different fungal species,” added Monosson.

Why are fungi becoming more of a threat?

Only “a fraction” of fungi species infect humans, said Geddes in The Guardian, but “they are responsible for roughly a billion infections each year”.

People with healthy immune systems can usually fight off fungal infections before they become dangerous, however. And most fungal diseases are not transmitted from person to person, but are instead picked up from the environment.

By contrast, viruses spread much faster than fungi and mutate, on average, more than 10,000 times faster. Scientific – and public – attention has long focused on the threat that viruses pose to humanity, specifically influenza, bird flu or a Sars-like coronavirus like that which caused the Covid-19 pandemic.

Given these fears about viruses, hit video game-turned-TV series The Last Of Us, in which a fungal pandemic causes society to collapse, appears to be telling “a mesmerising whopper”, said NPR. But “there’s growing evidence – real evidence – that climate change may in fact make this class of pathogens more dangerous to humans”.

Most fungi cannot survive the human body temperature, so fungal infections have, “for the greater part of the history of humankind,” never been a threat to human health, said Rachael Dangarembizi, a neuroinfections researcher at the University of Cape Town, on The Conversation. Now, however, “climate change and other environmental pressures have led to the emergence of species of fungi that are capable of surviving at human body temperatures”.

There are “many reasons to fear a new fungal pathogen”, warned Monosson in Time. These range from “the paucity of antifungal drug options to lack of vaccines and diagnostic difficulties in humans, to the potential for catastrophic crop and wildlife disease”.

For example, around 6,000 species of fungi are known to cause disease in commercial plants, and each year 40% of the world’s rice crops are lost to a fungal disease, posing a huge threat to global food supply.

The world’s susceptibility to fungal pathogens is “genuine”, agreed climate website Grist, but “when the real fungal pandemic comes, it won’t look like anything you’ve seen on screen”.

Are there cures?

Fungal infections already kill around two million people each year globally – more than either TB or malaria – and the death toll is increasing.

As “they become more prevalent and resistant to the handful of antifungal treatments available today”, said The Scientist, fungal pathogens are emerging as a “significant threat to human health”.

Alarmingly, there are no human vaccines against fungi.

The US Centers for Disease Control and Prevention recently warned that a drug-resistant and potentially deadly fungus has been spreading rapidly through the country’s healthcare facilities.

Yet scientists have been slow to react to the emerging global threat, possibly because “most of the population affected by fungal infections live in rural or poor urban settlements”, Dangarembizi suggested on The Conversation.

Another possible reason is that fungi predominantly infect people who already have major health problems, so “primary cause of death will probably be leukaemia or heart transplant, or whatever”, Mark Ramsdale, an associate professor at the MRC Centre for Medical Mycology in Exeter, told The Guardian.

The area of fungal diseases currently receives less than 1.5% of all infectious disease research funding globally, but there are signs this could be changing. In October, the World Health Organization (WHO) released a fungal priority pathogens list, the first ever global effort to create a mycological “most wanted” list of the 19 fungi most dangerous to humans.

“Despite posing a growing threat to human health, fungal infections receive very little attention and resources globally,” the report said. “This all makes it impossible to estimate the exact burden of fungal infections, and consequently difficult to galvanise policy and programmatic action.”

With so many fungal species on our planet, “watching out for emerging threats is a daunting task”, said Geddes in The Guardian. And “underestimating them would be a mistake”.