California health authorities are warning people not to eat foraged mushrooms after nearly two dozen people were sickened — including one person who died — in cases likely linked to the death cap mushroom (Amanita phalloides).
The California Department of Public Health (CDPH) said there have been 21 confirmed cases of toxic mushroom poisoning between mid-November and last Friday, which officials say are “likely” tied to death caps. Toxins from the mushrooms caused one adult fatality and severe liver injury in children and other adults; several patients required intensive care and at least one person may have needed a liver transplant.
Officials reported “significant clusters” of cases in the Monterey and San Francisco Bay areas, but warned the risk exists statewide. CDPH director Dr. Erica Pan advised against foraging wild mushrooms during the high-risk season because death caps can be easily mistaken for edible varieties. The mushrooms are known to grow across much of California and thrive after fall and winter rains; an unusually rainy season this year has created especially favorable conditions.
Death caps are implicated in the majority of fatal mushroom poisonings worldwide and have been reported in many U.S. regions, including the Midwest, Northeast and Mountain West. Recent sightings include Boise, Idaho. In California, death caps likely arrived in the 1930s on the roots of imported European oaks and have since become established in many areas, with Northern California noted as a hotspot.
Where they grow
Amanita phalloides typically forms associations with oak, pine and other hardwood trees and is often found in urban and suburban settings rather than deep forests. They commonly appear in small, widely spaced groups, which puts them close to where people and pets live and play.
What they look like
Death caps can resemble edible mushrooms, particularly in their young “button” stage. They are medium to large, sometimes reaching about 6 inches across and tall, with a greenish-gray cap that flattens with age, white gills, a white ring on the stem and a large white sac (volva) at the base. They can smell and taste pleasant, giving no obvious warning of their toxicity.
How poisonous they are
Death caps contain the peptide toxin α-amanitin (AMA), which is highly toxic and resistant to heat, cold, drying and stomach acid. Ingesting even a small amount — half a cap or less — can be lethal. Mortality after ingestion has been reported as high as 50% in some series, and scientists estimate death caps cause roughly 10,000 illnesses and about 100 deaths globally each year. Worldwide, the species accounts for a large share of mushroom-related fatalities.
Symptoms and progression
Symptoms of AMA poisoning are characteristically delayed, usually beginning six to 15 hours after ingestion but sometimes as late as 48 hours. The typical early signs are severe abdominal pain, persistent vomiting, profuse watery diarrhea and extreme thirst; this initial phase may last about a day. After this, a temporary seeming recovery often occurs, but is followed by rapid deterioration with severe weakness, restlessness, and pain as liver, kidney, heart and skeletal muscle damage develops. Without effective treatment, the illness can progress to coma and death within four to eight days. If recovery occurs, it often requires at least a month and may involve enlargement of the liver.
Treatment and research
There are limited specific treatments. Medical care focuses on symptom management and reducing toxin absorption: activated charcoal may be given early, and high doses of penicillin have been used. A botanical extract, silibinin, is also used in some cases and can help protect the liver. In severe poisonings, liver transplantation may be necessary.
Recent laboratory research has offered some hope for new therapies. Studies in mice found that the FDA-approved medical dye indocyanine green (ICG) reduced AMA toxicity, but human trials are needed to determine safety and effectiveness in people.
Public guidance
Because death caps are hard to distinguish from edible mushrooms and can be deadly, California officials urge people to avoid foraging wild mushrooms and to eat only mushrooms purchased from reputable commercial sources. Anyone who begins to experience gastrointestinal symptoms after eating foraged mushrooms should seek medical care immediately and inform clinicians about possible mushroom ingestion.