Mushrooms: A Toxic Foray

Mushrooms have been consumed by humans since prehistory, but mushroom toxicity has also been known for millennia, even implicated in the death of historical figures like the Roman Emperor Claudius. While most mushrooms are not toxic, out of the vast number of mushroom species, there are about 100 that are toxic, and only a few of the 70-80 species of poisonous mushrooms are fatal when ingested. Poisonous mushrooms contain differing toxins that cause various types of harm, from slight gastrointestinal discomfort to death. The most common toxin causing severe poisoning and the most fatalities is amatoxin, which blocks DNA replication and leads to cell death. Other deadly mushrooms include the destroying angels, deadly dapperling, deadly webcaps, Chlorophyllum molybdites, and Entoloma.

Toxic mushrooms often resemble edible mushrooms, leading to accidental poisoning

Out of the thousands of mushroom species, only about 100 are toxic. However, toxic mushrooms often closely resemble edible mushrooms in colour and morphology, which can lead to accidental poisoning. For instance, the deadly dapperling, which contains amatoxins, has been mistaken for edible varieties, and the destroying angel, which is one of the world's most toxic mushrooms, resembles edible button mushrooms. The deadly webcap and fool's webcap are also similar in appearance to each other and to several edible varieties.

Mushroom poisoning can range from slight gastrointestinal discomfort to death. The symptoms depend on the toxin ingested, which could include amatoxin, psilocybin, muscarine, coprine, allenic norleucine, or gyromitrin. Amatoxin, for example, blocks DNA replication, leading to cell death and potential liver failure. Orellanin, found in the deadly webcap, has a long latency period and may take up to three weeks to cause symptoms, often leading to a misdiagnosis.

To prevent mushroom poisoning, foragers should familiarize themselves with the mushrooms they intend to collect and their toxic doppelgangers. Taste tests can be misleading, as some poisonous mushrooms can have a pleasant taste. While handling toxic mushrooms will not lead to poisoning, ingestion of even small amounts can be dangerous.

If mushroom poisoning is suspected, early symptoms (within 6 hours of ingestion) can be treated with stomach irrigation, fluid-electrolyte balance maintenance, forced diuresis, and activated charcoal administration. Late toxicities (symptom onset after 6 hours) are life-threatening and require intensive care.

Amatoxin is the most common toxin causing severe mushroom poisoning

Out of the thousands of mushroom species, only about 50 to 100 are toxic to humans. Of these toxic species, the most common toxin causing severe mushroom poisoning is amatoxin. Amatoxin is a cyclopeptide toxin that blocks the replication of DNA, leading to cell death. It is synthesized by some Amanita, Galerina, and Lepiota species, with the Amanita species being responsible for the majority of mushroom toxicity cases in humans. Amatoxins interfere with protein synthesis and cause liver failure. They can also cause the loss of muscle contraction, kidney failure, and central nervous system damage.

The Amanita phalloides, or "death cap", is a type of mushroom named for its substantial amount of amatoxin, about 10 mg per mushroom, which is the lethal dose. Other common amatoxin-containing mushrooms include Amanita virosa (destroying angel), Amanita verna (fool's mushroom), Amanita bisporigera, Galerina autumnalis (autumn skullcap), and Galerina sulcipes. The deadly dapperling, widely distributed throughout Europe and parts of Asia, also contains amatoxins. While poisonings from this mushroom are not very common, they can be lethal if immediate treatment is not received.

Amatoxin poisoning is treatable if quick, professional care is received. Certain specialty laboratories can measure serum concentrations of amatoxin in the blood, though the test is not always reliable and is often negative once symptoms begin. Treatment options include N-acetyl-cysteine, penicillin, silymarin, and activated charcoal. The key factor that determines the outcome of poisoning is the amount consumed. Amatoxin poisoning is a serious issue, causing 95% of deaths from mushroom ingestion worldwide.

Some mushrooms contain less toxic compounds, and poisoning responds well to treatment

While many mushrooms are toxic and can cause severe poisoning, it is important to note that not all mushrooms are equally poisonous. Some mushrooms contain less toxic compounds, and poisoning caused by these mushrooms may respond well to treatment.

Mushroom poisoning occurs due to the ingestion of mushrooms containing toxic substances called mushroom toxins or mycotoxins. These toxins are secondary metabolites produced by the fungus, and they can cause a broad range of symptoms, from slight gastrointestinal discomfort to severe liver and kidney failure, and even death. The severity of mushroom poisoning depends on various factors, including the species of mushroom, the specific toxins it contains, and the amount ingested.

Some mushrooms, such as the deadly dapperling, while containing amatoxins, are not very common causes of poisoning. Poisoning from these mushrooms may respond better to treatment, especially if immediate medical attention is sought. Additionally, certain mushrooms may become less toxic when cooked or prepared properly. For example, ibotenic acid in some mushrooms can decarboxylate into muscimol upon curing, rendering it relatively non-toxic. However, death via respiratory depression is still possible, and muscimol intoxication is often considered unpleasant.

It is worth noting that the toxicity of mushrooms can vary even within the same species. For instance, the "death cap" and "destroying angel" mushrooms, both from the Amanita genus, contain amatoxins, which are highly toxic and can lead to liver and kidney failure. However, other species in the same genus, such as Amanita pantherina, may be less toxic and cause less severe symptoms. Nevertheless, it is always recommended to seek expert help immediately if mushroom poisoning is suspected, as timely treatment can significantly improve outcomes.

The management of mushroom poisoning typically involves supportive care and, in some cases, the administration of antidotes such as N-acetylcysteine, pyridoxine, methylene blue, atropine, and glycopyrrolate, as recommended by toxicologists. Additionally, nursing staff and physicians must be vigilant in identifying nonspecific gastrointestinal symptoms that could be indicative of mushroom toxin ingestion, especially in regions where toxic mushrooms are prevalent. Seeking medical attention promptly and providing a detailed history, including a description of the mushroom and the amount ingested, can greatly aid in the treatment process.

Milkcaps are mostly toxic and exude a milky substance from their gills

Out of the thousands of mushroom species, only about 100 are toxic. However, the toxins in these mushrooms can cause severe harm, and even death. Amatoxin, for example, blocks DNA replication, leading to cell death and potential liver failure. Other toxins include psilocybin, muscarine, coprine, and more. Many mushroom poisonings occur due to the misidentification of toxic mushrooms as edible ones. Some toxic mushrooms bear a striking resemblance to edible varieties, making them especially dangerous.

One such mushroom is the milkcap, which is distinguished by the thin milky substance it discharges when its gills are cut. Milkcaps are mycorrhizal, meaning they form relationships with tree roots, and are found on the ground rather than on logs or trees. While some milkcaps are edible, such as the carrot orange-coloured saffron milky caps, others are toxic. The bleeding milkcap, for instance, grows with conifer trees in western North America and exudes red latex "milk" from its pores.

The best way to ensure safe foraging is to learn the characteristics of the mushrooms growing in your surroundings. For instance, saffron milky caps have a cap that is 3-5 inches wide, with orange gills that run slightly down the stem. The stem is also orange and thick, ranging from 1-3 inches long. This variety of milkcap seems to prefer conifers, especially northern white cedar and eastern white pine.

Another variety of milkcap is the Lactarius thyinos, which is found in the northeastern United States and Canada. This species is unique among Lactarius mushrooms in that its caps and stems do not bruise green when handled. Instead, its orange milk slowly stains the surrounding flesh red.

Poisonous mushrooms may emit an unpleasant smell, discouraging consumption

While there are only about 100 toxic mushroom species out of the vast number of mushroom species, they are responsible for around 6000 ingestions in the United States annually. Mushroom poisoning usually occurs when toxic mushrooms are misidentified as edible species. This is because toxic mushrooms often closely resemble edible mushrooms in terms of colour and general morphology. For example, the "destroying angel" is a highly toxic mushroom that resembles edible button mushrooms and meadow mushrooms. Similarly, the deadly dapperling, which contains amatoxins, is often mistaken for edible varieties.

To prevent mushroom poisoning, it is recommended that only mushrooms purchased from a reputable source, such as a supermarket or greengrocer, be consumed. If foraging for mushrooms, it is crucial to familiarize oneself with both the desired mushroom species and any similar-looking toxic species. Some toxic mushrooms may also emit an unpleasant smell, discouraging consumption. For instance, the Agaricus Xanthodermus, or yellow-staining mushroom, gives off a chemical smell like disinfectant, iodine, or kerosene. This smell can become even stronger when the mushroom is cooked. Toxic members of the Agaricus family also smell chemically and unpleasantly of Indian ink or iodine.

While some argue that colour can serve as a warning signal, with toxic and edible mushrooms differing in colour, others refute this theory, noting that many mushroom predators are nocturnal and have poor vision. Instead, it is suggested that observable characteristics, or phenotypes, may co-occur with toxicity, acting as warning signals. One such characteristic is aposematism, which is a physical trait that warns off predators. Another potential warning signal is olfactory aposematism, where the unpleasant odour of the mushroom deters predation.

It is important to note that cooking, peeling, drying, or soaking a mushroom does not always make it safe to eat. If there is any uncertainty about the edibility of a mushroom, it is best not to consume it. If mushroom poisoning is suspected, immediate medical attention should be sought, and a sample or photo of the mushroom should be provided to aid in identification and risk assessment.

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