Fungi have had a fleeting presence in our lives – but that may be about to change

With the advent of Sars-CoV-2 and the Covid pandemic, the world of viruses suddenly became a lot more visible to the non-scientific public. The availability of antibiotics ensured bacteria have been part of our daily discourse for decades.

But what of the third element of microbiological life?

Fungi have, at most, had a fleeting presence in our lives. But that may be about to change. Not to the extent depicted in the TV adaptation of The Last of Us, it must be said. This show depicts a post-apocalyptic world where society has collapsed due to the outbreak of a dangerous, brain-controlling fungal infection that turns humans into hostile, cannibalistic “zombies”.

[ Socioeconomics, travel and contact with pets driving up fungal infections ]

But global warming could turn some fungi into life-threatening bugs: most fungi like colder temperatures around 10℃, meaning they’re typically unable to grow at the human body’s internal temperature of 37℃. This is one reason why most fungal infections in humans tend to stay on the skin where it’s cooler. It’s also why only a small number of fungi are able to cause infections in humans relative to the size of the fungal kingdom.

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Warming global temperatures mean fungi must adapt. This may increase the number of species which can cause serious infections in humans, according to Rebecca Drummond, associate professor of immunology and immunotherapy at the University of Birmingham. There is “some evidence to suggest this may already be happening”, she says.

Diagnosing an infection can be difficult, as it presents with a broad range of symptoms including fever, chills, headaches and nausea

Writing recently in The Conversation, Drummond points to the fungus Candida auris as a cause of extreme concern, since it’s resistant to nearly all antifungal drugs. It can spread rapidly around hospitals and care homes, causing serious infections in people with weak immune systems.

But what really makes Candida auris stand out is its ability to grow at higher temperatures – it’s able to withstand up to 42℃.

Candida auris emerged in three continents almost simultaneously, with experts concerned the warming global climate may have contributed to its rise. It is the first to have multiple international health alerts associated with it. It has been found in more than 30 countries since it was first identified in Japan in 2009.

[ Yeast of burden: deadly new strain of fungal infection has scientists rattled ]

Whether further global temperature increases leads to more dangerous fungal superbugs remains to be seen.

Candida auris has some unusual features which make it different from some other fungi: it can grow on human skin, for instance. This means people who have been colonised by Candida auris can shed lots of fungus from their skin, and this then contaminates bed clothes and surfaces.

While it is unusual for a fungal infection to spread from person to person, that seems to be how Candida auris infections spread. Outbreaks can happen with this organism, especially in intensive care units (ICUs) and nursing homes.

Despite this easy spread, most people who become colonised by Candida auris will not get ill from it, or even know it is present. It causes infections when it gets into surgical wounds or into the bloodstream from an intravenous line. Once it gets into the body, it can infect organs and the blood, causing a serious and potentially fatal disease.

The mortality rate for people infected with the fungus – as opposed to those whose skin becomes colonised – is between 30 and 60 per cent. But a precise death rate remains elusive, as people who are infected are often critically ill with other conditions.

Diagnosing an infection can be difficult, as it presents with a broad range of symptoms including fever, chills, headaches and nausea. The tests for infection can be difficult to identify accurately.

[ Over 35,000 annual deaths in Europe linked to drug-resistant superbugs – report ]

Interestingly, the rising numbers of Candida auris infections are thought to be partially linked to the Covid pandemic. People who become very ill from Covid may need mechanical ventilation and long stays in the ICU, which are both risk factors for Candida auris colonisation and infection.

The new bug is dangerous for those who become infected.

mhouston@irishtimes.com