Science

Prof Arturo Casadevall: ‘It is hubris to think a fungal pandemic can’t happen to us’


Arturo Casadevall is a professor of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health. He has spent four decades investigating how fungi can both improve and devastate life as we know it. His new book, What If Fungi Win?, charts how we might overcome the rising threat.

What first fascinated you about fungi?
When I was in training as an infectious disease fellow [in the 1980s], Aids was the biggest problem we had. Patients were not dying of HIV infections [which attack the immune system, leaving it vulnerable to other diseases], they were dying of opportunistic infections – and these were often fungal. This was the first large-scale human fungal crisis in history. Once I began working on the medical side of fungi, I discovered the wonders of this kingdom.

The award-winning series The Last of Us charts a world where a fungus triggers the apocalypse. Could that happen?
Improbable, but not impossible. Right now, we don’t know of any fungus that can turn a human into a zombie. But there’s no question in my mind that we’re likely to see dangerous new fungal pathogens emerge in time. In fact, we are already seeing it happen. So who knows?

In your book, you describe the climate crisis as a major risk for fungi developing beyond our control. Why is that?
Everything in our environment is being affected as temperatures rise; there’s no reason to believe fungi will be an exception. As modern medicine paradoxically creates more people who are vulnerable to new fungal infections, there’s increasing evidence that certain fungi have the potential to unleash new diseases that will harm many more humans in unprecedented ways.

What would happen if fungi could adapt to higher temperatures? They would jump over our defences. Are we then going to see many more fungal diseases? That is the fear.

Has this happened already?
Candida auris was unknown to medicine until 2007 when it was recovered from the ear of an individual in Japan. And then a few years later, in 2010, 2011, 2012, it emerges independently on three continents [South America, Africa and the Indian subcontinent].

The HBO series The Last of Us, based on the hit game, is set in a world devastated by a fungal pandemic. Photograph: Chris Large/HBO

So we have a medical mystery. We have an organism that medicine didn’t know anything about. One of the things that we have proposed is that this may have been the first fungus to breach our thermal barriers [most fungi cannot survive at 37C degrees, the body’s internal temperature] after adapting to higher temperatures. It is likely the first example of a new fungal disease emerging from climate change.

Can fungi be harnessed for good?
Fungi are critical elements for life on Earth. They benefit us in foodstuffs – you can’t have wine without fungi, you can’t have fermentation without fungi. They are the source of groundbreaking medicines, such as penicillin and statins. Innovators are using fungi to make vegan leather car seats and construction materials. Others are using them to degrade the plastics that fill our landfills. Going forward, they may be sources of new materials, things that could make our everyday life better.

Could they be used for more sinister ends?
You always worry about engineering organisms for evil. I don’t know that it’s being done by anybody. But certainly [for] a kingdom that is so large and so diverse and has so many powerful species, that has to be on the radar – that bad actors could use it in some way. They make powerful toxins, so they have been considered as agents for biological warfare. There are nefarious uses with fungi but, generally, the good and the potential good that they do far, far outweighs the negatives.

How could they be used for biological warfare?
Many of the fungi make spores, and the spores are designed to be carried in the wind. Generally when people make biological warfare, they have to change the organism so it can be dispersed by air. Well, the fungi come ready-made to be dispersed by air.

An illustration of Candida auris, first found in Japan, now present on three continents. Photograph: Science Photo Library/Alamy

Could they cause a pandemic?
Humanity does not have experience with a fungal pandemic, but other species do. The amphibians are being decimated by a fungus that has spread to all the continents. So if a fungus can do that to amphibians that have been around for millions of years and which have good immune systems like we do, then I think it is hubris to think that something can’t happen to us. We have a huge blind spot when it comes to the diseases and toxins fungi can wield.

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What are the biggest challenges in fighting back against fungi?
Because fungi are our closest relatives, it’s hard to find drugs that kill them and don’t hurt us. Then there is the economic explanation. Many fungal diseases are not as common [as others], and if you’re a pharmaceutical company and you’re thinking about where to put your money, you often [make the decision] based on market size. Progress is being made, but we have a long way to go.

In terms of your own research, what are you most excited about?
It turns out that fungi, most of them, make melanin, the same melanin that we have in our skin. This melanin has a lot of properties that can be harnessed. For example, melanin is a natural shield for radiation. [It] is almost like science fiction, but we are working with Nasa collaborators on the idea that melanin from fungi can be used for shielding for spacecraft.

I’m also excited about some of the progress that we are making in understanding how fungi cause disease. If you understand the mechanisms, you may be able to interfere with them – and if you can interfere with them, you can help people.

You’ve spoken out about the rise of counterfeit research being driven by “fraudulent data and sloppy science”. How widespread is the problem?
I’ve been very worried for a long time that science is not working as well as it should. We have done studies showing that there was an epidemic of retractions. Why is that? Well, we found out that there was a significant amount of misconduct. That’s totally intolerable.

I look at this almost like an existential problem. If science doesn’t work, it’s not going to give humanity the tools it needs. And if people lose confidence in us [scientists], they’re going to cut the funding, and then it’s all going to be a downward spiral. Less funding, less science, less solutions.

The name of the book is What If Fungi Win?. What if they do win?
I think they already won. And I think that if they win, we win.



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