Cornell Mushroom Blog

Lawrence Millman wrote this post, drawing info and inspiration from Student X, who explored the issue in my Medical and Veterinary Mycology class last year.

Welcome to Tasmania, an island that’s part temperate rainforest, part high country wilderness, and part gentle English countryside. In keeping with the theory of topographic resonance, which proposes that the inhabitants of a place somehow reflect that place’s geography, the island’s most iconic resident, the platypus, is also a surreal mingling of parts. With its duck-like beak, its beaver-like tail, its otter-shaped body, and (in males) its venom glands, the platypus would seem to have stolen parts from other mammals, not to mention reptiles. Perhaps birds too: female platypuses lay eggs.

Sometimes the platypus will even have a pinkish coloration on its legs or tail. Might this be a theft from a flamingo? Not at all. The pink color may indicate that the animal is suffering from a fungal infection called mucormycosis. Specifically, it has one or more lesions caused by Mucor amphibiorum, a fungus that typically targets (as its name suggests) amphibians.

Fact: Mucor is a genus of molds (zygomycetes) mostly found in the ground, on plant surfaces, rotting vegetables, and — since 1982 — on platypuses.

Mucor amphibiorum isn’t native to Tasmania, but if you’re a fungus, you’re happy to go non-native. All you need is someone or something to vector your spores, and off those spores go. Quite a few European and Asian species, including the Death Cap (Amanita phalloides) and Radulomyces copelandii, have traveled to North America in the last century. Mucor amphibiorum itself probably came over from mainland Australia with infected frogs, and having arrived, doubtless bided its time until an unsuspecting platypus happened to saunter along…

Curiously, the fungus does not seem to affect mainland animals. Perhaps the cooler body temperatures of Tasmanian platypuses, a response to the island’s own cooler temperatures, encourages its growth on a local host. Perhaps the fact that Tasmania is an island refuge limits that host’s genetic diversity, thus making it more susceptible to M. amphibiorum. Indeed, island biogeography is probably the reason the Tasmanian devil is so vulnerable to the so-called Devil Facial Tumor Disease (which is caused by a cancer, not a fungus).

Note: Mycology is a science of perhapses. That’s one of the reasons why it’s so interesting.

Some platypuses have dermal lesions all over their bodies. The fungus can form small round cells that travel in-platypus to start new lesions in new places. You can’t help but feel pity for the poor animals. At the same time, it’s hard not to admire the opportunistic nature of the fungus that’s causing all the trouble: a new island, a new host, and there’s more of me, its presence seems to say.

So we’ve got an infected platypus: will it survive, or will it succumb? If the lesions aren’t severe and don’t spread, the animal might return to a healthy state. But if the lesions are invaded by bacteria, or new lesions impair internal organs, the platypus could become so debilitated that it can’t forage for food or maintain its body temperature. Whereupon pneumonitis, a secondary infection, or starvation could deliver the coup de grâce.

I know what you’re thinking: can I, a somewhat more advanced creature than a platypus, be infected by a Mucor species? The answer is yes…if you have a badly compromised immune system or an extensive flesh injury. If you inhale the spores of certain Mucor species, you might develop a potentially fatal, but extremely uncommon disease called rhinocerebral mucormycosis. But you’re ten thousand times, no, a hundred thousand times more likely to have a mucor infection on your bread — i.e., “black bread mold” (Rhizopus stolonifer) — than you are to have one in your body.

Query: Tasmania seems to specialize in extinctions. Its last full-blood aboriginal native, Truganini died in 1876; the last Tasmanian wolf probably died in 1936; and the Tasmanian devil is currently at risk because of Devil Facial Tumor Disease. Will the platypus be next?

Here’s an animal that’s secretive, nocturnal, semi-aquatic, and burrow-dwelling, so it’s difficult to determine what percentage of the island’s population is might be affected by mucormycosis. Two recent (2009) studies suggest that far fewer platypuses are suffering from the disease now than twenty years ago. Thus it would seem that Tasmanian platypuses, like their mainland brethren, have developed some sort of immunity to the fungus. Still, the abstract of one of the studies concludes with this statement of uncertainty: “…the individual consequences of infestion are poorly understood and require further investigation.” Welcome to Kingdom Fungi!

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