It’s not every day you read about suggestions for potential health-related travel advisories to U.S. states. But such is the case for the Pacific Northwest, where an emerging fungal infection has — very unusually for fungi — begun felling otherwise healthy people. A growing number of cases of the potentially fatal disease cryptococcosis have been diagnosed in people who merely traveled to Washington, Oregon, or British Columbia.
There are several very scary things about this fungus, but foremost among them is that it a) was introduced somehow from the tropics, most likely South America/Brazil or also possibly Africa and is somehow not finding it a problem to survive in Canada; b) is actively spreading up and down the Pacific Northwest coast; c)hangs out in the environment, where it can get along apparently fine without us (and seems to particularly like the bark of and soil around trees like Eucalyptus); d) is acquired from the environment, that is, you don’t have to have contacted with an infected person or animal; e) doesn’t manifest itself symptomatically for 2-12 months after one picks it up and e) can kill otherwise healthy people.
So let’s review. This means that you can just be hiking along in the woods, minding your own business, and a few months later you’re dead. Now I’m not saying this is *common*. Only 200 people have been seriously affected in 10 years. And let’s face it, there are a lot of other things that can kill you while hiking along minding your own business, much, much quicker and more commonly than these fungi: bears, mountain lions, lightning, exposure, rockfalls, your own stupidity, deranged axe murderers, errant militias, etc. But the very fact that, like anthrax, you can pick it up for no apparent reason from the environment, and much more easily, is disturbing. (Histoplasmosis is also picked up by inhalation but it is well known you must spend time around bird or bat droppings. Aside: can you think of any other diseases that are picked up just by inhalation from the wild?)
This particular organism is Cryptococcus gattii, a relative of the Cryptoccoccus neoformans that gained some fame in infecting AIDS patients when the immune disease emerged in the ’80s. Cryptococcosis begins as a lung infection, but can progress to meningitis. C. gattii, a cousin of C. neoformans, first emerged on Vancouver Island in 1999, but in the last few years, two new strains have emerged that seem to be killing otherwise healthy people in numbers much higher than earlier strains.
There are anti-fungal drugs that can help show C. gattii the door, but the wikipedia article for C. gattii contains this ominous sentence:
Antifungals alone are often insufficient to cure C. gattii infections, and surgery to resect infected lung (lobectomy) or brain is often required.
Resectioning *brain*??! Oh hell no.
Fortunately, infection with this organism remains relatively rare, but that’s no guarantee of safety. Why? This fungus is having sex. And that is one possible origin of the two newly virulent strains that have emerged in the Pacific Northwest — and possibly the source of future, more dangerous strains. It is also possible that the two new strains were newly introduced from their tropical diversity centers. But the scientists *know* there’s a lot of C. gattii hanky-panky going on. They looked at a couple dozen genetic markers in this recent PLoS study, and compared which isolates had which markers and how they were organized in the genome. They also tried to reconstruct the evolutionary and geographic relationships between various North American isolates using these data. They found huge genetic diversity among their isolates, and that at least one north American strain came from Australia. They also that the fungus is bumping up its numbers by quick and easy asexual reproduction.
But the initial creation of the new hyper-virulent types, they concluded, was likely due to sex. Only sexual reproduction provides the opportunity for lots of large-scale genome reorganization; that’s one of sex’s main advantages. When two entire genomes get together, a process called “crossing over” takes place that allows all the various chromosomes to swap corresponding bits. The result is sometimes good, sometimes bad, but whatever the outcome, generation of diversity and evolution often happen a heck of a lot faster per generation with sex than without.
Lest you think that’s the only worrying bit, it turns out that this fungus has a rather kinky sex life. Not only is it having sex with all the other mating types (fungi often have many “genders”, which for convenience scientists refer to as “mating types”), it can also, somewhat unusually for fungi, have sex (and I mean produce viable offspring) with its own type, a process called unisexual mating. Sheesh.
So that’s what was chiefly covered in the news reports. But it turns out there’s more to this story. Because this fungus is actually a yeast — an infectious yeast. Now I know what you may be thinking: yeast are the source of everything good and worthy on Earth: fresh, crusty, heavenly leavened bread, wine, beer, soy sauce, etc. And you’re right. But that doesn’t mean there aren’t evil yeast. Nasty yeast. Parasitic yeast. Because “yeast” is a lifestyle, not a taxonomic group or single species.
The yeast you’re probably most familiar with, Saccharomyces cerevisiae, commonly called baker’s yeast, is but one fungus that has adopted this way of life. And that way of life is: forsaking multicellularity for swingin’ single cellhood. In a way, yeast have devolved (although that’s a bit misleading; it doesn’t mean they’re less adapted or successful than they were before; just that being unicellular is more like their long-ago ancestors). The standard fungal body plan today is a multicellular filament, or tube. The tube branches, and the collection of branched tubes makes up the fungal body, or cottony “mycelium” we are familiar with from the surface of refrigerator contents gone rogue. Yeast are fungi that have given up this form, and have gone back to single celled living, a bit like a protist. It would be as if all your spleen cells decided that they’d rather just go off and live on their own in pond water — they’re sick and tired of cleaning up your bloodstream, thank you very much! — and they want out of the cooperative.
But it gets more complicated than that. Some fungi can go back and forth between their normal, filamentous lifestyle and the yeast lifestyle. Histoplasmosis, mentioned earlier, can do this. In the wild, it is a brownish mycelium that lives in bird droppings and bat guano. Once inhaled and installed in your lungs, it becomes a yeast. Cryptococcus neoformans and Cryptococcus gattii are among this group too. Sometimes they are filamentous. Sometimes not.
And here’s where it gets really weird. Because yeast is a lifestyle, not a taxonomic group (like a genus or family), yeast come from all over the fungal family tree. Baker’s yeast is an ascomycete like morels and truffles. But C. gattii is . . . a yeast evolved from the jelly fungi! Jelly fungi are super-awesome amazing organisms in the basidiomyctes (a major division in the fungi, like ascomycetes, that make their sexual cells on special pronged cells called basidia) that usually decay wood and produce fantastically fun-to-touch-and-play-with fruiting bodies that are gelatinous and sometimes quite colorful.For reference, here is what one looks like:
The jelly fungus you might be familiar with, if you are familiar with one at all, is the wood ear mushroom*, Auricularia auricula, commonly used in Asian cuisines — in particular, in hot and sour soup. Again, these fungi are perfectly innocuous. Some fungi produce very different forms when they live asexually or sexually. Because they’re so different, mycologists often give the sexual form a different name from the asexual form (an explanation of whether this is a good idea and why mycologists continue the practice could take up a book). The sexual jelly fungus form of C. gattii is Filobasidiella bacillispora, although it’s not necessarily the case that the jelly form would produce a structure big enough for you to see with your naked eye. I know of no jelly fungi that can hurt you either by touch or consumption. But the yeast form of these particular fungi apparently can. Weird!
A larger question might be: what are these fungi doing in us? Are they only accidental parasites? What are they doing out in the wild when they aren’t infecting us? As they say . . . further studies are needed.
But in the meantime, the weirdness parade goes on. C. gattii has *also* been isolated from a regular menagerie of other mammals, including koalas, llamas and. . . are you ready for this? . . . dolphins. How dolphins managed to spend time frolicking in the woods (or how the fungus managed to spend time frolicking with dolphins) is a subject for another blogger.
*According to the Wikipedia article, the Japanese name for these jelly fungi is “tree jellyfish”(!) Sometimes literal foreign phrases smack you upside the head with a perfectly obvious insight you never thought of before.
Byrnes, E., Li, W., Lewit, Y., Ma, H., Voelz, K., Ren, P., Carter, D., Chaturvedi, V., Bildfell, R., May, R., & Heitman, J. (2010). Emergence and Pathogenicity of Highly Virulent Cryptococcus gattii Genotypes in the Northwest United States PLoS Pathogens, 6 (4) DOI: 10.1371/journal.ppat.1000850