Scientists estimate that roughly 1.5 million species of fungus inhabit the Earth, but only a handful are capable of causing human disease.
Problem is, when they do, fungi can be remarkably lethal: For example, about half the patients who develop serious infections from the fungus Aspergillus will not survive. The mortality rate for the most common fungal infection in hospitals, candidiasis, has been reported to be just as high — and . . . overall fungal infection rates have been on the rise. . . .
[S]ometimes, when conditions are right, a fungus starts to germinate while its host is still among the living. In people, this generally leads to troublesome, but not fatal, infections of the skin and nails.
“Most fungal pathogens are pretty wimpy . . . They are not very good at causing disease in normal hosts with normal immune systems.”
But a growing population of people have not-so normal immune systems. Fungal infections are so deadly in part because most patients who become seriously ill are already weakened by AIDS, cancer, transplants or medications that handicap the body’s ability to mount a strong defense. More and more of these patients have taken high doses of antibiotics to prevent other infections, fundamentally changing the body’s ecology and allowing unnatural fungal growths to take over. More patients are also undergoing medical procedures that breach normal immune barriers with catheters and other devices.
One particularly troubling fungal infection that doesn't seem to follow the usual trend of limiting itself to those already vulnerable is "Cryptococcus gattii [which] has been slowly spreading since at least 1999 across the Pacific Northwest, where it has caused more than 200 severe brain and lung infections and killed 24 people."
This class of fungal infection has long been a problem in South America, Southeast Asia and Australia.
Fungal spores are ubiquitous and mostly beneficial, so broad spectrum anti-fungal treatments of surfaces may not be desirable. Interestingly, unlike viruses, where much of your immunity is specific to a particular kind of virus ("adaptive immunity"), most of the body's immune defenses from fungi are generalized defense not specific to any particular kind of fungus ("innate immunity").
New research is trying to identify medical strategies for treating these diseases, which are more similar to humans biochemically than most other pathogens by better understanding them and is making progress, at least on the understanding front.