California authorities are warning people not to eat foraged mushrooms for the time being after nearly two dozen people were sickened — including one fatally — by a highly poisonous mushroom known as the death cap.
The California Department of Public Health (CDPH) said in its advisory that there have been 21 confirmed cases of toxic mushroom poisoning — which it says is "likely" from consumption of death caps — between mid-November and last Friday.
Toxins from the mushrooms killed one adult and caused severe liver damage in kids and other adults. Several patients required intensive care, "with at least one individual potentially needing a liver transplant," health officials added.
Officials said there have been "significant clusters" of cases reported in the Monterey and San Francisco Bay Areas, but are warning of risk statewide.
"Because the death cap can easily be mistaken for edible safe mushrooms, we advise the public not to forage for wild mushrooms at all during this high-risk season," said CDPH director Dr. Erica Pan.
Death cap mushrooms are known to grow in many parts of California, fueled especially by the fall and winter rain.
An unusually rainy season has created particularly favorable growing conditions for the mushrooms, as was the case in December 2016, when state officials reported 14 cases of death cap poisoning. All of the individuals survived, but three required liver transplants and one child had "permanent neurologic impairment."
Death caps may thrive in California, but they are not limited to the state. The highly poisonous species is responsible for 90% of mushroom-related fatalities worldwide.
Death cap sightings and poisonings have been reported across the Midwest, Northeast and Mountain West in recent years. Most recently, in October, the Idaho Department of Health and Welfare reported that the "world's deadliest mushrooms" had been spotted in Boise.
Where do death caps grow?
Death cap mushrooms, or Amanita phalloides, originated in Eurasia but are now found in many other places, including North America and Australia — where they were implicated in a high-profile mass murder case earlier this year. (The U.K. conservation charity Woodland Trust says they have been an "invisible murder weapon for millennia," blamed in the deaths of Roman Emperor Claudius in 54 AD and Holy Roman Emperor Charles VI in 1740.)
They are thought to have arrived in Central California in the 1930s by accident, via the roots of imported European oaks, and have taken hold across the state — and beyond — in the decades since.
"It's intriguing because it's from one place, and it's spreading in another place," Anne Pringle, a mycologist at the University of Wisconsin-Madison, told NPR in September, pointing to Northern California as a death cap "hot spot."
Death cap mushrooms typically grow near oak, pine and other hardwood trees, often in widely spaced groups. They tend to be more common in urban and suburban wooded areas, as opposed to forests.
"They're just inherently around places where people are," Britt Bunyard, a mycologist and editor-in-chief of FUNGI Magazine, told member station KQED.
That makes them a significant threat to people and pets, especially considering they don't look too different from other kinds of harmless mushrooms.
What makes them so poisonous?
Death cap mushrooms are similar in appearance and taste to other edible varieties, like puffballs, especially in their young "button" stage.
They are typically medium-to-large in size — growing up to 6 inches across and 6 inches tall — with a greenish-gray cap that is initially dome-shaped but flattens out over time. They have white gills, a white ring around the stem and a large white sac at the base of the stem.
Bunyard says the death cap mushroom actually smells and tastes "quite nice," leaving "no hint that it's poisonous in any way."
But they got their name for a reason.
Eating half a cap or less could be enough to kill a person, with the mortality rates after ingestion reaching as high as 50%.
While death cap mushroom poisonings are hard to track, some scientists estimate that they cause about 10,000 illnesses and 100 deaths around the world each year.
What happens after eating them?
Death cap mushrooms produce a highly toxic peptide called α-Amanitin, or AMA, which is resistant to heat, cold, drying, freezing and stomach acid.
The Food and Drug Administration (FDA) says AMA poisoning is characterized by the delayed onset of symptoms, starting on average after six to 15 hours, but potentially up to 48 hours. They manifest in sudden stomach pain, persistent vomiting and watery diarrhea and extreme thirst that may only last a day.
"If this early phase is survived, the patient may appear to recover for a short time, but this period generally will be followed by a rapid and severe loss of strength, prostration, and restlessness caused by pain," the FDA says.
It explains that the disease causes "irreversible" liver, kidney, cardiac and skeletal-muscle damage, often ending in a coma and death after four to eight days.
"If recovery occurs, it generally requires at least a month and is accompanied by enlargement of the liver," the FDA adds.
There are few effective treatments for death cap poisoning. Doctors tend to treat symptoms by administering activated charcoal, large doses of penicillin and a newer drug called silibinin, as well as rehydration and, in some cases, liver transplants.
But recent discoveries have offered hope for a potential antidote.
In 2023, Chinese and Australian researchers revealed that they found the FDA-approved medical dye ICG effective in treating AMA poisoning in mice. But without human trials, it's not entirely clear how well the drug works in treating people with death cap poisoning.
That's why California health officials want people to only eat mushrooms from reputable commercial sources — and, if they do start having symptoms, go to a hospital immediately.
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