Infections of Cryptococcus neoformans are rare among healthy people, but the fungus ravages those with compromised immune systems. It is spread primarily by the guano of pigeons and contracted by inhaling spores. More than 1 million immunosuppressed patients are infected annually around the world, according to figures from the Centers for Disease Control and Prevention. The worst affected sufferers live in sub-Saharan Africa, where mortality rates from the fungus among AIDS sufferers reach 70 percent.
As we tear up forests and turn over soil, we unleash spores from their slumber, including species that humans and other animals have rarely encountered before. World trade is helping strains of fungus spread and hybridize. And our wanton use of antibacterial medicine, including in farm animals, kills the microbes that could help keep fungus levels in check.
“The environment is changing quite dramatically,” Heitman said. “Logging, gardening, forestry, and other things that perturb the environment and move around soil or trees that are contaminated with the fungus are a major contributor.”
Fungus doesn’t just eat away at our organs and cells; it tucks voraciously into our food. Moldy bread can be a minor bother, but fungal agricultural pandemics have the potential to occur on a staggering scale. Researchers writing in Nature calculated that the known fungal pathogens could wipe out more than one-third of the world’s supply of major crops if severe epidemics struck simultaneously. And they point out that diseases such as rice blast and wheat rust are already having a major impact on agricultural productivity: “Our calculations show that even low-level persistent disease leads to losses that, if mitigated, would be sufficient to feed 8.5 percent of the 7 billion humans alive in 2011.”
This year, 39 people have died and 581 others have been sickened after mold spores infiltrated immunosuppressant medicine. The tainted drugs were injected directly into patients’ central nervous systems, where the fungus blossomed.
Doctors in desert regions of the Southwestern United States have reported a recent spike in cases of Valley Fever. In this painful and sometimes fatal ailment, a fungus that occurs naturally in the soil passes through the nose or mouth and settles inside the lungs. Once there, it sets down its mycelia roots and begins to eat. In 2007, 4,815 people were reported sickened by the fungus disease in Arizona. In 2011, 16,473 contracted the disease. It appears to be particularly abundant near decomposing animal carcasses. It might have originally specialized in decaying animals and then adapted to feeding on living tissue.
A fungus that once was limited to tropical regions has been spreading and killing people in the Pacific Northwest since it was discovered in 1999 on Vancouver Island. Cryptococcus gattii can cause pneumonia and meningitis, ravaging otherwise healthy sufferers. It has since been detected in Idaho, California, and farther north in Canada.
Researchers are racing to develop vaccines against some of the most deadly fungal pathogens. Anti-fungal medicines are readily available; they work by damaging fungal membranes and cell walls. But because we’re so closely related, potent medicines that damage fungal cells can also harm the human organs they were designed to protect.
The scourge of fungal contagions will continue to worsen, particularly among those with compromised immune systems. There appear to be no immediate threats that human fungal outbreaks will parallel the plagues afflicting bats and frogs. That’s largely because our body temperatures are warmer and less hospitable for fungus than those of amphibians and hibernating mammals. Also to our advantage, some of the most deadly fungal diseases afflicting humanity today are contracted after spores are kicked up from the environment and into our bodies—not spread from person to person, as was the case for the Black Death and Spanish flu, which were caused by a bacterium and virus, respectively.
But other fungal diseases do already spread from person to person, such as through sex, as in the case of yeast infections. If new strains of deadly fungi evolve similar abilities to jump directly from person to person, or from wild or farm animals to humans, new diseases could run rampant.
And some of the same scientists who speculate that fungi killed off the cold-blooded dinosaurs during a time of global cooling warn that global warming could help similar pathogens adapt to withstand our warm blood. If that happens, we will lose our best defense against fungal plagues, and our opportunistic kinfolk would be poised to overwhelm humanity with crippling bouts of their cell-sucking ruination.