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New Test Strips Detect Harmful Toxin in Some Common California Mushrooms

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Amatoxin test strips developed by the USDA look a lot like pregnancy tests and are as easy to perform. (Chloe Veltman/KQED)

In a parking lot near some woods about an hour east of San Francisco, United States Department of Agriculture (USDA) research microbiologist Candace Bever rummages around in a box containing plastic containers, slides and tubes.

“I’m going to grab a vial here,” she says. “And my saline solution.”

We’ve just picked an assortment of mushrooms on a hike. One of them, a paddy straw mushroom, looks suspiciously like a specimen she’s brought along with her — Amanita phalloides, also known as the death cap.

Amanita phalloides (death cap) mushrooms in the wild. (Candace Bever)

Bever is demonstrating a simple, portable new test she’s developed with her team at the USDA’s Western Regional Research Center in Albany, California to detect a dangerous poison known as amatoxin that’s found in some common California fungi. The test yields results in minutes.

“All you need is a rice size piece of the mushroom,” Bever says, putting samples of the death cap and the paddy straw in a pair of vials filled with saline solution. She then shakes the vials and dabs a few drops of each liquid onto the ends of two white, plastic strips.


It looks a lot like a pregnancy test.

After a few minutes, two pink lines emerge in the window of the paddy straw test strip. That’s a negative result. But only one line forms in the window of the other strip — the one with the Amanita phalloides sample.

Amatoxin test equipment. (Chkloe Veltman/KQED)

“So that is a positive for amatoxins,” Bever says.

Bever says death cap fatalities are currently rare. According to 2018 data from the Poison Control Center, there were only 76 Amanita phalloides poisoning cases reported nationwide. Around half of these required treatment at a health care facility. None resulted in death.

But the death rate might rise, because Amanita phalloides is an invasive species.

“Its range continues to spread,” Bever says of the fungi, which was accidentally introduced from Europe into Northern California in the 1930s, and can now be found all over the state and beyond.

Mushroom expert and Bay Area Mycological Society co-founder Debbie Viess says it’s hard for the average person to distinguish between the harmful death cap, which has white gills and spores and a skirt, and benign lookalikes such as the paddy straw.

Microbiologist Candace Bever (left) and mycologist Debbie Viess pose with a paddy straw mushroom. The benign paddy straw is often mistaken for the harmful death cap. (Chloe Veltman/KQED)

“So this could be a death cap,” she says, examining a paddy straw mushroom. “Except it has pink gills and spores and it doesn’t have a skirt.”

The new strips also test urine — not just mushroom samples.

So Viess says they could help doctors and nurses figure out if amatoxin is the cause of a poisoning and quickly respond to the symptoms.

“Where this test is valuable is in a clinical situation, where you have somebody who’s poisoned and you don’t know what poisoned them,” Viess says. “If you can eliminate or confirm it’s amatoxin, you can save this person’s life.”

Existing methods for detecting amatoxins involve noxious chemicals, or require high-end equipment only found in a lab. California Poison Control toxicologist Eddie Garcia says this gives the USDA’s new test strips an edge.

“The ease of use is the real advance here,” he says.

But Garcia says it’ll be years before the strips are approved for medical staff to use them on patients in a hospital or doctor’s office.

“We shouldn’t jump to conclusions that this can be used in humans quite yet to detect dangerous poisoning,” he says.

The strips are expected to roll out for commercial use sometime later this year under the brand name Amatoxtest.

“We’re going to try to keep the price below $100 for three strips,” says Richard Ransom, the owner of Michigan-based Amatoxtest LLC, which is licensing the technology. “How much less will depend a bit on demand and a final cost accounting.  They may end up being pretty cheap, perhaps as low as $10 or so apiece.”

Screenshot from one of many Facebook groups where mushroom lovers have been exchanging comments about the new amatoxin test strips. (Facebook)

Some mushroom community members have already taken to Facebook to complain about the new test strips, fearing they might encourage careless foraging and lead to death.

“Hooray!” wrote user Steve Moore on the Georgia Mushrooming Facebook page with his tongue firmly in his cheek. “I don’t have to learn all of those stupid scientific names or spend my time learning what different mushrooms look like anymore. I can just depend on a government made doohickey to keep me safe!”

Mushroom expert Debbie Viess has been participating in the discussions on social media. She defends the value of the strips for their potential clinical use. But she also says when it comes to safely identifying fungi, there’s no substitute for true knowledge.

“I think you would be foolish to rely on a test rather than your eyes,” Viess says.

While some fungi enthusiasts might be wary of the strips, they could find a fanbase among dog lovers and veterinarians.

Mushroom poisoning is a canine hazard, and the new test works on dog urine.

“Any diagnostic tests available to the veterinary community are often appreciated because we don’t have the same level of resources as human medicine,” says veterinarian and researcher Catherine Hagan, who’s based in the Sacramento area, and says she has seen many dog mushroom poisoning cases in California over the years. “So when a pet comes in and you’re trying to narrow down what the problem is, any tool you have available to you that’s reliable, repeatable and affordable I think is valuable.”

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