Death cap mushroom poisonings spike in California : NPR

Death cap mushrooms look like other edible varieties, but are very toxic. They grow near oaks and other hardwood trees, usually in urban and suburban areas.

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William West/AFP via Getty Images

California authorities are warning people not to eat harvested mushrooms at this time after nearly two dozen people were sickened – one fatally – by a highly toxic mushroom known as 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 are “likely” due to consumption of the deadly capsules — between mid-November and last Friday.

Toxins from the mushrooms killed one adult and caused severe liver damage in children and other adults. Several patients required intensive care, “with at least one individual potentially requiring a liver transplant,” health officials added.

Officials said there had been “significant clusters” of cases reported in the Monterey and San Francisco Bay areas, but warned of a statewide risk.

“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,” said CDPH Director Dr. Erica Pan.

Death cap mushrooms are known to grow in many areas of California, fueled in particular by fall and winter rains.

An unusually rainy season created particularly favorable growing conditions for mushrooms, as was the case in December 2016, when state officials reported 14 cases of deadly cap poisoning. All individuals survived, but three required liver transplants and one child suffered “permanent neurological impairment.”

Deadly caps may thrive in California, but they’re not limited to the state. This highly toxic species is responsible for 90% of mushroom-related deaths worldwide.

Deadly cap sightings and poisonings have been reported in 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 phalloidesoriginally from Eurasia, but now found in many other places, including North America and Australia – where they were involved in a high-profile mass murder case earlier this year. (British conservation charity Woodland Trust says they have been an “unseen murder weapon for millennia”, blamed for the deaths of the Roman Emperor Claudius in AD 54 and the Holy Roman Emperor Charles VI in 1740.)

They are believed to have arrived in Central California in the 1930s by accident, via the roots of imported European oaks, and took hold throughout the state – and beyond – in the decades that followed.

“It’s intriguing because it’s coming from one place and spreading to another place,” Anne Pringle, a mycologist at the University of Wisconsin-Madison, told NPR in September, pointing to Northern California as a “hot spot” of the death cap.

Deathcap mushrooms typically grow near oaks, pines, and other deciduous trees, often in widely spaced groups. They tend to be more common in urban and suburban wooded areas, as opposed to forests.

“They are inherently found around places where people are,” Britt Bunyard, mycologist and editor-in-chief of MUSHROOM Magazinetold member station KQED.

This makes them a significant threat to people and pets, especially since they are not too different from other types of harmless fungi.

What makes them so toxic?

Death cap mushrooms are similar in appearance and taste to other edible varieties, such as puffballs, especially in the young “button” stage.

They are typically medium to large in size – reaching 6 inches in diameter and 6 inches in height – with a greenish-gray cap that is initially dome-shaped but flattens 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 deathcap mushroom has a “rather pleasant” smell and taste, leaving “no indication that it is toxic in any way.”

But they got their name for a reason.

Eating half a capful or less could be enough to kill a person, with the mortality rate after ingestion reaching up to 50%.

Although deadly mushroom poisonings are difficult to track, some scientists estimate that they cause about 10,000 illnesses and 100 deaths worldwide each year.

What happens after eating them?

Deathcap 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) states that AMA poisoning is characterized by delayed onset of symptoms, beginning on average after six to 15 hours, but potentially up to 48 hours. They manifest as sudden stomach pain, persistent vomiting, watery diarrhea and extreme thirst that may last only a day.

“If one survives this early phase, the patient may appear to recover for a short period, but this period will usually be followed by rapid and severe loss of strength, prostration, and agitation caused by pain,” the FDA explains.

He explains that the disease causes “irreversible” damage to the liver, kidneys, heart and skeletal muscles, often ending in coma and death after four to eight days.

“If recovery occurs, it usually takes at least a month and is accompanied by liver enlargement,” the FDA adds.

There are few effective treatments for lethal cap poisoning. Doctors tend to treat symptoms by giving activated charcoal, high doses of penicillin and a new drug called silibinin, as well as rehydrating and, in some cases, performing liver transplants.

But recent discoveries offer 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 lethal cap poisoning.

That’s why California health officials want people to only eat mushrooms from reputable commercial sources and, if they start showing symptoms, go to the hospital immediately.