Deadly mushrooms and friendly fungi

“They were in the garden, the house garden, and it’s an area where mushrooms grow. There are lots of different kinds of mushrooms… there are field mushrooms, there are portobello mushrooms.”

Husband-and-wife John Dexter and Mariah Alves were at their family farm in east Gippsland when their mealtime took a turn.

With an active and well-looked-after house veggie garden, the appearance of white, flat-topped mushrooms wasn’t viewed as suspicious, or hazardous. They were fried and plated-up that afternoon.

But while heading back to Melbourne a few hours later, John was on one end of the phone to the Victorian Poisons Information Centre while Mariah’s lunch was making its way onto the side of the road, in liquid form.

Poison control ran John through a series of detailed, but urgent questions: where were the mushrooms? What did they look like? Were photos available for identification?

In the dark of night, a call back to the farm meant no clear images were available, but John’s description – particularly the point that there are no oak trees on the property – meant good news.

Good news is relative when your partner is in a world of pain, but given the deadly death cap mushroom (Amanita phalloides) tends to grow at the base of oaks, it was more likely the troop of mushrooms in the family garden were the deceptive Agaricus xanthodermus – yellow-stainers.

“It got so bad at a point that John wasn’t even pulling over anymore for me to vomit – I just had a bag,” Mariah says.

“In our minds, we [thought] if we are to stop at a hospital, we might as well get to Melbourne as soon as we can.”

“Poison control also advised us, because they were yellow-stainers, there wasn’t much we could do,” John says.

“It would probably pass, and you would feel terrible, but you should just keep drinking water and take pain killers, and only go to hospital if it was really bad.

“When we were determining it and figuring it out, they said if was death caps you have to go to hospital as soon as you possibly can.”

As Mariah explains, “Because [I] would basically die of liver failure in 24 hours.”

Alpha-amanitin: the forager’s foe

Yellow-stainers are one thing, but death caps raise the stakes. Had Mariah ingested even a single death cap, the consequences would have been grim.

Death cap mushrooms and some of their related species, including several ominously dubbed ‘destroying angels’, contain a potent toxin called alpha-Amanitin.

α-Amanitin is an octapeptide – a molecule of eight amino acids assembled into ring structures – which is difficult to break.

“It’s highly resistant to degradation by heat,” says Dr Kylie Agnew-Francis, a medicinal chemist at the University of Queensland.

So cooking the sporing body of a mushroom won’t do much to break the toxin down. The enzymes in your body don’t fare any better at trying to degrade its structure.

This stubborn molecule is readily absorbed into the blood once it hits the intestines. Fortunately, we have our own toxin elimination system thanks to our livers and kidneys, right?

Wrong.

Within 6-24 hours, α-Amanitin leads to symptoms like nausea and vomiting. Worse, symptoms can subside after this initial onset, which can lull people into a false sense of security.

“Then, you start getting signs of liver toxicity,” Agnew-Francis says.

“At that point, it’s started to reach the liver and it’s taken very easily into the liver, and into cells in the liver.

“When it gets into those cells, it binds very well to an enzyme called RNA polymerase-II.”

This binding inhibits these important enzymes from performing their role in expressing liver cell genes. As Agnew-Francis puts it, the introduction of α-Amanitin in the liver quickly leads to cell death.

“And it’s very good at doing it,” she says.

“Once you get to that point, where you’re starting to get the liver toxicity effects, the survival rate can be quite low. You’ll see different numbers all over the place, but mortality rates vary between 30% up to about 90%.”

Even in survivors, organ failure is common, and not just for the liver, but the kidneys as well, as α-Amanitin can be reabsorbed into the bloodstream and make its way into other parts of the body.

Cruelly, the very organs intended to get toxins from the body, tend to meet their match in α-Amanitin.

Regardless of safety protocols, you can’t farm a death cap

In light of the recent fatal poisonings in Leongatha, the Australian Mushroom Growers Association has been at pains to drive home the safety protocols of supermarket producers, with its leaders saying its safety protocols made it impossible for a deadly species to make its way into a carton of white mushies.

Agaricus bisporus – part of a different genus – are the most widely grown and eaten mushrooms in the world. It’s the species name for all white, button, Swiss brown and portobello mushrooms. These are the fungal staples of markets and grocery stores across the globe, and almost always grown in carefully managed commercial farms.

But it’s not just the fact commercial growers choose to grow Agaricus bisporus that makes it impossible for a deadly outlier to make its way into your local supermarket.

Dr Michael Taylor, a mycologist at Flinders University, says an important point has been missed in the rush to assure the public of food safety; one that would further support commercial growers.

“This mushroom cannot be farmed,” Taylor says.

By that, he means death cap mushrooms couldn’t be grown in a commercial garden, even if someone tried.

“Ecologically, it can only grow in association with tree roots.”

This is why John and Mariah were specifically asked by poison control about whether the mushrooms she ate were growing near oak trees. Basidiomycetes are fungi that produce mushrooms, which are actually the fungus’ reproductive sporing bodies. These often form associations with other organisms – in the case of death caps, its relationship with oak, birch and elm trees can provide the fungus with a valuable source of carbon.

“You could never farm it in the lab, you couldn’t grow it in a commercial horticultural setup, that’s a pretty key point, you couldn’t ever accidentally grow it,” Taylor says.

Appreciating mushrooms – especially LBMs – safely

Globally, the Amanita genus contains some of the most toxic known mushroom species and accounts for most mushroom-related deaths.

You could never farm it in the lab, you couldn’t grow it in a commercial horticultural setup.

Dr Michael Taylor

Its poster child is Amanita muscaria ­– or fly agaric – the fairy tale mushroom with a red cap dotted by tiny white splotches.

But not all fungal species are so obviously marked – death caps and many other Amanita species appear quite plain. And outside of the Amanita family are hundreds of thousands of other known, and unknown fungi that are also hard to pick out.

Take Agaricus xanthodermus, our yellow-stainers that likely caused Mariah’s nausea and vomiting between Gippsland and Melbourne – they’re cousins of our supermarket staple Agaricus bisporus and look remarkably similar, save for their little yellow bruises.

In light of the highly-publicised death cap tragedy in Leongatha, public health authorities across Australia have again emphasised the risks of amateur mushroom foraging. It’s illegal in some states and territories to collect natural products from public spaces like national parks and protected areas, but authorities also regularly issue ‘do not pick’ notices, in respect of wild mushroom foraging.

Experts who work with fungi like Agnew-Francis and Taylor say education and awareness are critical to avoid future fatal and non-fatal poisonings.

With potentially hundreds of thousands of unknown species in Australia, the risk of species misidentification is high. Migrants and visitors from Europe and Asia – where there are long-established foraging traditions – may be especially ill-equipped to identify Australia’s own endemic species. Among mycologists, the very nature of their work exposes them to innumerate unknown fungi: what they call ‘LBMs’ or little brown mushrooms.

“Mushrooms are very good at looking like other mushrooms,” says Agnew-Francis.

“It’s very easy to misidentify them, which is why knowing how to identify them is very, very important if you’re going foraging.”

Non-fatal poisoning incidents often happen – whether through forager misidentification or a child grabbing what’s at hand on the garden lawn. Fatalities are far less common, though several have been reported in Australia across the last decade.

Mushrooms are very good at looking like other mushrooms.

Dr Kylie Agnew-Francis

But it’s unfair on fungi – and foragers – to create a culture of fear around the myriad of weird and wonderful mushrooms sticking up from the ground in ecosystems around us. And so ensuring good public education around the benefits and risks of fungi, as with wild plants and animals, should be an important consideration when poisonings occur.

“They’re not going to reach out and grab you and poison you. You’re not going to, just by seeing them, be sick; we shouldn’t go cutting down oak trees,” Taylor says.

“You’re totally safe to go out to the forest and walk around. You’re not in any peril, enjoy the world around you and as part of that, understand it enjoy the organisms that grow there.”

For John and Mariah, their experience has been a cautionary one.

“I’m definitely cautious of food that’s been foraged,” John says. “That experience makes you appreciate that there are poisonous things in the world that grow naturally.”

And as for poor Mariah, she’s still sticking to her white buttons from the supermarket.