Fungi: Yet Another Growing Threat to Humanity

 We are constantly reminded that our bodies exist in a swarm of microbes, some of which are critical parts of our bodies resulting from evolving in this swarm.  Pathogens occasionally enter our environment and cause problems.  Mostly they have been viruses and bacteria.  Emily Monosson, in her book Blight: Fungi and the Coming Pandemic, reminds us that there is another class of microbe, fungi, that is also part of the surrounding swarm.  She describes new forms of fungi that may be developing and spreading due to global warming.

Monosson tells us that there are an estimated six million or more different species of fungi, much more than the number of plant and animal species.  Their main function seems to be the breaking down of dead or once-living matter into its components for future use.

“Most fungi live if not in collaboration, then in peace with other living things.  But some do not.  Some feed on the living rather than the dead and dying.  Most fungi give life; fungal pathogens take it.”

“Some disease-causing fungi can survive in the environment for days or months or years even without a host.  Unlike many other pathogenic microbes, fungal spores can be remarkably persistent, and each single spore carries the instructions for a next generation of mold, mildew, smut, or myriad other fungi.”

“Collectively, infectious fungi and fungus-like pathogens are the most devastating disease agents known on the planet.  The incidence of novel fungal diseases across species, including humans, has risen over the past century.”

Like other of the Earth’s microbes, fungi evolve over time as they look for new hosts to invade.  Infectious diseases will find a host and generally devastate the population, but not necessarily eliminate it.  A few specimens will possess genetic makeups that allow them to survive the onslaught and rebuild a population that can survive the endemic pathogen.  What is dangerous is when hosts are unknowingly transported across the globe where the pathogen finds plenty of new hosts to infect, leading to a pandemic.

“The pandemics and epidemics I write about in these pages all began with a fungus that was moved from its home environment to a completely new setting where it happened upon a suitable host.  There are a lot of fungi in the world.  Although most are harmless, a few can cause utter devastation when provided with a novel and susceptible host.  Our job going forward will be to prevent the potentially harmful fungi from meeting the susceptible host—including us.”

Much of what Monosson discusses relates to plant life.  Trees and other foliage are in constant danger of infection.  Agricultural crops have always had to contend with unruly fungi.  Recent fungal infections have appeared among bats and amphibians, decimating their populations and spreading across the globe. 

Could something similar happen to humans?  The author’s book title suggests an answer in the affirmative.  Has something changed to make fungal infections more likely?  Perhaps so.  Consider that our mammalian body with its high temperature microbiome has provided an inhospitable environment for fungi.

“For much of our existence our microbiome has helped to keep potentially invasive microbes—particularly those already in residence—in check.  Most of those microbes are bacteria that in both number and diversity have the fungi beat.  There is a good reason for this: our body temperature.  Many bacteria thrive at 37ºC (98.6ºF), the normal human internal temperature, but for many fungi our bodies are like Death Valley.  Most fungi prefer temperatures between 12ºC (53.6ºF) to 30ºC (86ºF).  We mammals simply run too hot.  Like a healthy microbiome, our warmth protects us from fungal invasion.  But now some scientists worry that our so-called temperature barrier is beginning to fail us.”

What has changed recently is that the climate has become warmer in most locations, providing more opportunities for fungi to develop a tolerance for higher temperatures.  And regions where high-temperature fungal infections already exist can spread into new regions with fresh potential hosts.

“In 2010 [Arturo] Casedevall and Monica Garcia-Solache coauthored an opinion piece for a scientific journal.  They hypothesized that warmer temperatures would alter and likely increase the geographic range of disease-causing fungi and likely select for new fungi pathogens with higher tolerances for a warm body.  In 2019, less than a decade later, Casadevell and colleagues suggested that the emergence of C. Auris may be the first example of a climate-enabled novel human fungal pathogen.”

C. Auris is short for Candida auris, a form of yeast that was first observed as an infection in relatively cool ears in 2006.  By 2009 it was observed to have entered the blood stream of three people, killing two of them.  In 2015, a fungal outbreak in Pakistan led to the CDC identifying C. Auris as the culprit.

“A year later C. Auris began popping up in other locales around the globe, including a handful of cases, diagnosed retrospectively, in the United States, which is when the CDC issued its first warning about the emergent disease.  Once the warning went out, other cases were identified.  Hundreds of cases in the United States and thousands of cases globally have since been reported.”

“In April 2019 the New York Times published a story about a patient who had been hospitalized at Mount Sinai in Brooklyn, New York, with C Auris.  He died three months later.  By then the yeast had colonized the entire room.  Dr. Scott Lorin, the hospital’s president told the Times that ‘everything was positive—the walls, the bed, the doors, the curtains, the phones, the sink, the whiteboard, the poles, the pump.  The mattress, the bed rails, the canister holes, the window shades, the ceiling, everything in the room was positive’.”

The mortality rate for infected patients varies between 30 and 60 percent.  Various strains of C. Auris exist, with resistance to most or all antifungal drugs.

C. Auris is an example of a suddenly appearing new pathogen; more are likely to follow.  Others already exist and appear to be growing in infection rate.  Valley Fever is a fungal disease endemic to warm and dry climates of the southwestern US and Mexico.  It is expected to spread throughout the western states in the coming decades.  During the covid pandemic, India saw a huge growth of cases of the fungal disease mucormycosis.  Thousands of cases emerged with a mortality rate of 85 percent.

New fungal strains are decimating bat and amphibian populations.  Thus far, humans have been spared a pandemic, but the fungi are gathering strength, and one might be inevitable.