A killer wild mushroom often mistaken for edible varieties has claimed the lives of four people and left at least 36 poisoned. Eating death cap fungus is fatal in around 50% of cases as it contains toxins which attack the liver causing it to shut down completely. 

The mushroom, amanita phalloides, is responsible for 90% of mushroom-related poisonings worldwide because foragers often mistake it for non-toxic edible fungus. Since November 18, the death cap has killed four people in the US state of California and left three others needing liver transplants. 

According to Californian authorities, many who sought medical attention suffered from rapidly evolving acute liver injury and liver failure and needed to be admitted into intensive care units. The patients have ranged in age from just 19 months old to 67 years old, the ages of those who died have not yet been released. 

The sudden spike in cases in the US has alarmed experts, who typically only see between two and five death cap poisoning cases a year. Dr. Craig Smollin, medical director for the San Francisco Division of the California Poison Control System, said: “The main thing this year is just the magnitude, the number of people ingesting this mushroom, having almost 40 is very unusual.”

Eating even a small amount of a death cap can be fatal and it doesn’t matter if the fungus is dried or cooked. 

Laura Marcelino, 36, told the San Francisco Chronicle that her family in the Northern California town of Salinas gathered mushrooms that looked like the ones she and her husband used to forage in their native Oaxaca, a state in Southern Mexico.

Ms Marcelino, 36, added her family “thought it was safe” but then her husband was dizzy and tired the next day, but Ms Marcelino felt fine, and they ate the mushrooms again, heating them up in a soup with tortillas. Their kids don’t like mushrooms and so didn’t have any.

The next day, both adults, seasonal farmworkers, became ill with vomiting and stayed home from work.

Ms Marcelino spent five days in the hospital, while her husband had to undergo a liver transplant.

People can have stomach cramping, nausea, diarrhea or vomiting within 24 hours after ingesting a toxic mushroom and the situation can quickly deteriorate after that, experts say. Early symptoms may also go away within a day, but serious to fatal liver damage can still develop within two to three days.

Californian public health officials said those poisoned have included many Spanish, Mixteco, and Mandarin Chinese speakers and offical warnings have now been posted in different languages. Spanish was the primary language for more than 60% of people poisoned, according to the health department.

According to the Woodland Trust, death cap is fairly common in most parts of the UK and it can be found in mixed deciduous woods, often in widely spaced groups, and particularly under oak and beech.

On the trust website, it states: :With only a small amount of the cap being necessary to kill someone, and symptoms not always appearing straight away, they have been used as an invisible murder weapon for millennia.

“The Romans and ancient Greeks recognised it as a deadly poison. It is said that Agrippina murdered her husband, Roman Emperor Claudius, by mixing deathcap juice with Caesar’s mushrooms (Amanita caesarea). He died of poisoning a few days after the meal. Voltaire claimed that Charles VI died by deathcap poisoning.

“Thousands more have died when mistaking deathcaps for edible mushroom species, especially at the button stage.”

Fruiting season: July to November

Habitat: mixed deciduous woods, often in widely spaced groups, particularly under oak and beech

A large fungus growing up to 15cm across and 15cm tall with a domed or white cap – depending on age – on an off-white stem. Although it looks fairly inoffensive and similar to a number of edible mushrooms, it is deadly poisonous.

Fruitbody: a shiny olive-yellow to greenish-bronze cap, 5–15cm in diameter. Dome-shaped at first and flattening as it matures, darker in the middle with faint radiating fibres giving it a streaked appearance. It smells sickly sweet and rancid when old, though at the button stage is virtually odourless.

Gills/spores: underneath the cap, the gills are broad and free, pure white turning cream or even slightly pink as they age. The spores are smooth and are elliptical in shape and its spore print is white.

Stipe (stalk): the stem is off-white, 7–15cm high with a floppy ring. It is swollen at the base and sits in a bag, or volva.

Not to be confused with: false death cap (Amanita citrina), which smells strongly of raw potatoes. It is said to be edible but should be avoided because it is easily confused with death cap and its deadly cousin, destroying angel (Amanita virosa).