Millions of fungal species exist in the world, but only a few hundred can make people sick, such as Coccidioides. This fungus is peculiar as it can survive in desert conditions, rather than the expected dark, damp and cool environment. Furthermore, it does not wait for an animal to die before digesting it from the inside out. This fungus has been around for millennia, yet we still do not understand many things about it, including how it spreads in the soil.
The infection caused by Coccidioides is known as Coccidioidomycosis, Desert Rheumatism, San Joaquin Valley Fever, or Valley Fever. Symptoms of Valley Fever are similar to the flu, but can last for over a month. Some people develop fungal pneumonia, skin absences, or meningitis, which can be fatal. Fortunately, only about four in ten people ever develop symptoms, and outbreaks are rare. 97% of US Valley Fever cases occur in Arizona or California, but it is likely that the fungus is already present in other states.
Scientists believe that three systems are driving the spread of this mysterious fungus. First, the fungus releases spores into the air when the soil is disturbed, and these spores are inhaled by mammals. Second, desert rodents may be helping spread the fungus. Lastly, the fungus can go dormant in the lungs, and can infect almost any type of mammal. I hope you’re ready to talk about dehydrated rats. It works like this: a kangaroo rat or some other desert rodent inhales cocci while digging its burrow. The cocci either lays dormant in their lungs or the infection kills them. At that point the fungus is the first on the scene to devour the dead animal - by digesting its dead body until there’s nothing left. Fun fact: this is what cocci is doing to people with severe valley fever, while they’re alive. Their spinal column is being digested by this organism, and it just freaks me out. Either way, it’s the first one on the scene - not even the best competitor or the best at doing anything, it’s just there first. And so maybe that’s cocci’s strategy. When the rodent dies, cocci is released back into the soil and morphs back into its environmental form where it waits to be kicked up and inhaled by some other host.
If this is the case, then the more desert rodents living and dying, the more likely cocci can move through the soil. Which brings us to our third related factor: extreme weather. Heavy rains have been unleashing on the desert resulting in booms of vegetation. The surplus food leads to a surplus of rodents - plenty of hosts to breathe in the fungus. But the desert ultimately returns to a desert and heavy drought wipes out more and more of these infected rodents. When they die, cocci spread right back into the soil and the system starts again.
But we still don’t know if this is actually even happening, because of how little we understand about cocci itself. Proving the Endozoan Hypothesis would be a colossal effort that involves strapping trackers to a bunch of desert rodents. And finding cocci in the soil at all has proven difficult. The current tests don’t always detect it in the soil, even when it’s there.
Ultimately, cocci’s spread could be thanks to all of these factors combined, but there are still tons of unresolved questions. What we do know is that the US is getting warmer and that on its own could expand cocci’s range potentially making more people sick. One study estimates that cocci’s range could more than double by 2095, due to increasing arid conditions across the US. Pair all of this with rising rates of construction in the desert and population booms in cities like Phoenix, and it’s no surprise that Valley Fever cases are on the rise.
Researchers have another area of study right now: prevention. We have identified a vaccine candidate that is both safe and protective, very protective to mice. And now we’ve shown that in experimentally infected dogs, it protects them as well. And that vaccine is on its way.
But listen, despite my seemingly best efforts this piece doesn’t really exist to scare you or to get you to hyper focus on one specific freaky infection. This single fungus is one of a million examples of how our world is changing in small and mysterious ways, and how difficult it can sometimes be for science to keep up.