Poisonings from ‘death cap’ mushrooms in California prompt warning against foraging

After a series of “deadly hat” mushroom poisonings – including one fatality – California health officials are urging residents not to eat foraged mushrooms unless they are trained experts.

San Francisco Bay Area doctors have blamed the wild mushroom, also called Amanita phalloides, for 23 cases of poisoning reported to the California Poison Control System since Nov. 18, according to Dr. Craig Smollin, medical director of the system’s San Francisco division.

“All of these patients were involved in independent research for fungi in nature,” Smollin, a professor of emergency medicine at the University of California, San Francisco, said at a news conference Tuesday. “They all developed symptoms within the first 24 hours, including nausea, vomiting, diarrhea and abdominal pain. »

Smollin said some of the patients were part of cohorts that ate the same batch of foraged mushrooms. The largest group was about seven people, he said.

All patients were hospitalized, at least briefly. One died. Five remain hospitalized. One received a liver transplant and another is on a donation list awaiting a transplant, Smollin said. Patients range in age from 1½ to 56 years old.

Mushroom collectors said deathcap mushrooms are more prevalent in parts of California this season than in previous years, which could be to blame for the increase in poisonings.

“Any mushroom has years when it’s prolific and years when it’s not. … It has a very good season,” said Mike McCurdy, president of the Mycological Society of San Francisco. He said the deathcap was one of two main species he identified during an organized collective mushroom hunt last week, called a foray.

In a press release, California State Public Health Officer Dr. Erica Pan warned that “because deathcap can easily be confused with edible and harmless mushrooms, we advise the public not to forage for wild mushrooms at all during this high-risk season.” »

Dr. Cyrus Rangan, a pediatrician and medical toxicologist at the California Poison Control System, said the “blanket warning” is necessary because most people don’t have the expertise to identify which mushrooms are safe to eat.

Still, he said, “it’s rare to see a series of cases like this.”

The California Poison Control System said in a news release that some of the affected patients speak Spanish and may rely on foraging practices perfected outside the United States. Death cap mushrooms resemble other species in the genus Amanita that are commonly eaten in Central American countries, according to Heather Hallen-Adams, chair of toxicology for the North American Mycological Association. Because death caps are not often found in this region, foragers might not realize the potential risk of lookalikes in California, she said.

Anne Pringle, a professor of mycology at the University of Wisconsin-Madison, said there is a litany of poisoning cases in which people misidentify something because their experience is not relevant to a new region: “It’s a story that comes up again and again.” »

Over the past 10 years, mushroom picking has boomed in the Bay Area and other parts of the country. At the same time, information resources on mushroom toxicity – reliable or not – have also proliferated, including on social media, phone apps and artificial intelligence platforms. Experts say these sources should be viewed with skepticism.

Long-time mushroom hunters maintain that this practice can be done safely. McCurdy, who has been collecting and identifying mushrooms since the 1970s, said he bristles at the broad discouragement of foraging.

“No, it’s ridiculous… After an incident like this, their first instinct is to say don’t look for food,” he said. “Experienced mushroom collectors will not pay any attention to this.”

But McCurdy suggested that people seek out the expertise of local mycological societies, which are common in California, and think critically about what sources of information their lives can rely on.

Both Pringle and McCurdy said they have seen phone apps and social media forums misidentify mushrooms.

“I’ve seen AI-generated guides that are dangerous,” Pringle said.

The deathcap is an invasive species that originated in Europe and arrived in California in the 1930s, likely with imported nursery trees. The mushroom is usually a few inches tall with white gills, a pale yellow or green cap, and often a ring around the base of its stem.

The species is found on the West Coast and the East Coast, as well as Florida and Texas, according to Hallen-Adams, who is also an associate professor of food sciences at the University of Nebraska-Lincoln.

In California it usually grows near oak trees, but sometimes also pine trees. The body of the mushroom is usually connected to the roots of trees and develops in symbiosis with them.

The toxin in death cap mushrooms, called amatoxin, can damage the kidneys, liver and gastrointestinal tract if ingested. It disrupts the transcription of the genetic code and the production of proteins, which can lead to cell death.

Hallen-Adams said U.S. poison centers receive an average of about 52 calls involving amatoxin each year, but “a lot of things don’t get called into poison centers — take that with a grain of salt.”

Amatoxin poisoning is not the most common type caused by mushrooms, but it is the most dangerous, she added: “90% of fatal poisonings worldwide will be caused by amatoxin.”

It takes very little to make a person sick.

“One cubic centimeter of mushroom ingested could be a lethal dose,” Hallen-Adams said.

Symptoms of amatoxin poisoning often develop within a few hours, then improve before getting worse. There is no standard set of medical interventions that doctors rely on.

“It’s a very difficult fungus to test for,” Rangan said, and “also very difficult to treat.”

A drug that doctors have relied on to treat some California patients — called silibinin — is still experimental and difficult to obtain.

“All of our silibinin comes from Europe,” Hallen-Adams said.

Death cap fungi have continued to grow profusely since their introduction, and Pringle’s research has shown that the species can reproduce bisexually and unisexually – with a partner or alone, alone – giving it an evolutionary advantage.

“If Eve can make more of herself, she doesn’t need Adam,” Pringle said. “One of the things I’m really interested in is how to stop the invasion, how to cure a habitat of its death caps. And I don’t have any solutions to offer you at the moment.”