As It Happens

Australian stinging trees inject people with a venom-like neurotoxin: Study

The leaves of Australia's stinging trees look "a bit fuzzy and not that scary" when you first see them, says pain researcher Irina Vetter. But don't be fooled. 

Researcher Irina Vetter says the trees could help scientists develop better pain treatment

Australia's gympie-gympie tree, also known as Dendrocnide excelsa, has tiny silica needles on its leaves that inject a painful neurotoxin into the skin. (Emily Barker/Shutterstock )

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Australia's stinging trees have leaves that look "a bit fuzzy and not that scary" when you first see them, says pain researcher Irina Vetter. But don't be fooled. 

"If you look closely, you can see that the fuzziness is actually just tiny little silica needles that are filled with fluid, which really we can think about as a venom now," Vetter told As It Happens host Carol Off.

"And it gets injected into your skin sort of in a fashion like a hypodermic needle."

Vetter, a pain researcher at the University of Queensland, has co-authored a new study examining the molecular structure of the poison produced by Australia's Dendrocnide excelsa tree.

The researchers discovered the leaves produce a previously unidentified type of neurotoxin that targets pain receptors in much the same way as the venom of a poisonous spider or scorpion. 

The findings, published in the journal Science Advances, could have implications for how we treat chronic pain. 

'It's a bit unpleasant, to say the least'

Dendrocnide excelsa is part of a family of stinging trees in Australia, which are locally known as gympie-gympie trees.

Much like the common nettle found in North America and Europe, the gympie-gympie's leaves release a substance that causes a sharp burning and stinging sensation on the skin — but it's much, much worse.

"Over the hours, as it progresses, you get sort of weird buzzing, crawling and shooting pains. And this can actually be triggered for days and weeks afterwards just by having a shower, for example, or scratching the stung area," Vetter said. 

"It's a bit unpleasant, to say the least."

From far away, it looks like fuzz. But look closer and you'll see the gympie-gympie's leaves are covered in fluid-filled needles. (Submitted by Irina Vetter )

She would know. 

"I've encountered them just going for a bush walk. But I have occasionally sought out a sting on purpose to investigate a bit more what's going on," she said.

"This really started off as a bit of curiosity as to why the pain is so bad."

A defensive mechanism 

Vetter says the trees likely developed the neurotoxins for the same reason a bug or animal would secrete a poisonous venom — as a form of self-defence from creatures who would like to gobble them up. 

"It's a remarkable case of what we call convergent evolution. So nature has a problem. How do you deter a herbivore or a predator? And nature has come up with basically the same solution — these toxins that act on pain-sensing nerves," she said. 

A close-up of Dendrocnide excelsa leaves shows the tiny needles that inject a venom-like neurotoxin that causes severe and long-lasting pain. (Submitted by Irina Vetter)

But there are critters who munch on the gympie-gympie leaves without any trouble, including various insects, and small marsupials called the pademelon.

"So we're not quite sure whether the pademelon, for example, is just a very tough cookie or whether there's something else going on," Vetter said.

But the core purpose of her research, she says, is to better understand how pain works, so that we can better treat it.

"Because the pain is so long lasting, we're hoping that it might give us some information to understand how chronic pain develops," Vetter said.

The researchers have already created a synthetic compound of the neurotoxins — which they've named gympietides — for further study.

"The hope is that once you've found something that acts on a pain-sensing nerve to activate it, it's actually not that difficult to modify the chemical structure of it, to turn it into something that would block a pain signal," Vetter said. 

"Maybe we can make something useful out of this."

Written by Sheena Goodyear. Interview produced by Lisa Bryn Rundle.

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