Harmful effects from ingestion of toxic substances present in a mushroom
Medical condition
Mushroom poisoning is poisoning resulting from the ingestion of mushrooms that contain toxic substances. Symptoms can vary from slight gastrointestinal discomfort to death in about 10 days. Mushroom toxins are secondary metabolites produced by the fungus.
Mushroom poisoning is usually the result of ingestion of wild mushrooms after misidentification of a toxic mushroom as an edible species. The most common reason for this misidentification is a close resemblance in terms of color and general morphology of the toxic mushrooms species with edible species. To prevent mushroom poisoning, mushroom gatherers familiarize themselves with the mushrooms they intend to collect, as well as with any similar-looking toxic species. The safety of eating wild mushrooms may depend on methods of preparation for cooking. Some toxins, such as amatoxins, are thermostable and mushrooms containing such toxins will not be rendered safe to eat by cooking.
Signs and symptoms.
Poisonous mushrooms contain a variety of different toxins that can differ markedly in toxicity. Symptoms of mushroom poisoning may vary from gastric upset to organ failure resulting in death. Serious symptoms do not always occur immediately after eating, often not until the toxin attacks the kidney or liver, sometimes days or weeks later.
The most common consequence of mushroom poisoning is simply gastrointestinal upset. Most "poisonous" mushrooms contain gastrointestinal irritants that cause vomiting and diarrhea (sometimes requiring hospitalization), but usually no long-term damage. However, there are a number of recognized mushroom toxins with specific, and sometimes deadly, effects:
The period between ingestion and the onset of symptoms varies dramatically between toxins, some taking days to show symptoms identifiable as mushroom poisoning.
Causes.
 
New species of fungi are continuing to be discovered, with an estimated number of 800 new species registered annually. This, added to the fact that many investigations have recently reclassified some species of mushrooms from edible to poisonous has made older classifications insufficient at describing what now is known about the different species of fungi that are harmful to humans. It is now thought that of the approximately 100,000 known fungi species found worldwide, about 100 of them are poisonous to humans. However, by far the majority of mushroom poisonings are not fatal, and the majority of fatal poisonings are attributable to the "Amanita phalloides" mushroom.
A majority of these cases are due to mistaken identity. This is a common occurrence with "A. phalloides" in particular, due to its resemblance to the Asian paddy-straw mushroom, "Volvariella volvacea". Both are light-colored and covered with a universal veil when young.
"Amanitas" can be mistaken for other species, as well, in particular when immature. On at least one occasion they have been mistaken for "Coprinus comatus". In this case, the victim had some limited experience in identifying mushrooms, but did not take the time to correctly identify these particular mushrooms until after he began to experience symptoms of mushroom poisoning.
The author of "Mushrooms Demystified", David Arora cautions puffball-hunters to beware of "Amanita" "eggs", which are "Amanita"s still entirely encased in their universal veil. "Amanita"s at this stage are difficult to distinguish from puffballs. Foragers are encouraged to always cut the fruiting bodies of suspected puffballs in half, as this will reveal the outline of a developing "Amanita" should it be present within the structure.
A majority of mushroom poisonings, in general, are the result of small children, especially toddlers in the "grazing" stage, ingesting mushrooms found on the lawn. While this can happen with any mushroom, "Chlorophyllum molybdites" is often implicated due to its preference for growing in lawns. "C. molybdites" causes severe gastrointestinal upset but is not considered deadly poisonous.
A few poisonings are the result of misidentification while attempting to collect hallucinogenic mushrooms for recreational use. In 1981, one fatality and two hospitalizations occurred following consumption of "Galerina marginata", mistaken for a "Psilocybe" species. "Galerina" and "Psilocybe" species are both small, brown, and sticky, and can be found growing together. However, "Galerina" contains amatoxins, the same poison found in the deadly "Amanita" species. Another case reports kidney failure following ingestion of "Cortinarius orellanus", a mushroom containing orellanine.
It is natural that accidental ingestion of hallucinogenic species also occurs, but is rarely harmful when ingested in small quantities. Cases of serious toxicity have been reported in small children. "Amanita pantherina", while containing the same hallucinogens as "Amanita muscaria" (e.g., ibotenic acid and muscimol), has been more commonly associated with severe gastrointestinal upset than its better-known counterpart.
Although usually not fatal, "Omphalotus" spp., "Jack-o-lantern mushrooms", are another cause of sometimes significant toxicity. They are sometimes mistaken for chanterelles. Both are bright-orange and fruit at the same time of year, although "Omphalotus" grows on wood and has true gills rather than the veins of a "Cantharellus". They contain toxins known as illudins, which causes gastrointestinal symptoms.
Bioluminescent species are generally inedible and often mildly toxic.
"Clitocybe dealbata", which is occasionally mistaken for an oyster mushroom or other edible species contains muscarine.
Toxicities can also occur with collection of morels. Even true morels, if eaten raw, will cause gastrointestinal upset. Typically, morels are thoroughly cooked before eating. "Verpa bohemica", although referred to as "thimble morels" or "early morels" by some, have caused toxic effects in some individuals. "Gyromitra" spp., "false morels", are deadly poisonous if eaten raw. They contain a toxin called gyromitrin, which can cause neurotoxicity, gastrointestinal toxicity, and destruction of the blood cells. The Finns consume "Gyromitra esculenta" after parboiling, but this may not render the mushroom entirely safe, resulting in its being called the "fugu of the Finnish cuisine".
A more unusual toxin is coprine, a disulfiram-like compound that is harmless unless ingested within a few days of ingesting alcohol. It inhibits aldehyde dehydrogenase, an enzyme required for breaking down alcohol. Thus, the symptoms of toxicity are similar to being hung over—flushing, headache, nausea, palpitations, and, in severe cases, trouble breathing. "Coprinus" species, including "Coprinopsis atramentaria", contain coprine. "Coprinus comatus" does not, but it is best to avoid mixing alcohol with other members of this genus.
Recently, poisonings have also been associated with "Amanita smithiana". These poisonings may be due to orellanine, but the onset of symptoms occurs in 4 to 11 hours, which is much quicker than the 3 to 20 days normally associated with orellanine.
"Paxillus involutus" is also inedible when raw, but is eaten in Europe after pickling or parboiling. However, after the death of the German mycologist Dr. Julius Schäffer, it was discovered that the mushroom contains a toxin that can stimulate the immune system to attack its red blood cells. This reaction is rare but can occur even after safely eating the mushroom for many years. Similarly, "Tricholoma equestre" was widely considered edible and good, until it was connected with rare cases of rhabdomyolysis.
In the fall of 2004, thirteen deaths were associated with consumption of "Pleurocybella porrigens" or "angel's wings". In general, these mushrooms are considered edible. All the victims died of an acute brain disorder, and all had pre-existing kidney disease. The exact cause of the toxicity was not known at this time and the deaths cannot be definitively attributed to mushroom consumption.
However, mushroom poisoning is not always due to mistaken identity. For example, the highly toxic ergot "Claviceps purpurea", which grows on rye, is sometimes ground up with rye, unnoticed, and later consumed. This can cause devastating, even fatal, effects, called ergotism.
Cases of idiosyncratic or unusual reactions to fungi can also occur. Some are probably due to allergy, others to some other kind of sensitivity. It is not uncommon for a person to experience gastrointestinal upset associated with one particular mushroom species or genus.
Some mushrooms might concentrate toxins from their growth substrate, such as Chicken of the Woods growing on yew trees.
Poisonous mushrooms.
Of the most lethal mushrooms, five—the death cap ("A. phalloides"), the three destroying angels ("A. virosa", "A. bisporigera", and "A. ocreata"), and the fool's mushroom ("A. verna")—belong to the genus "Amanita", and two more—the deadly webcap ("C. rubellus"), and the fool's webcap ("C. orellanus")—are from the genus "Cortinarius". Several species of Galerina, Lepiota, and Conocybe also contain lethal amounts of amatoxins. Deadly species are listed in the List of deadly fungi.
The following species may cause great discomfort, sometimes requiring hospitalization, but are not considered deadly.
Evolution.
Many different species of mushrooms are poisonous and contain differing toxins that cause different types of harm. The most common toxin that causes severe poisoning is amatoxin, found in various mushroom species that cause the most fatalities every year. Amanita, or “ the death cap”, is a type of mushroom named for its substantial amount of amatoxin, which has about 10 mg per mushroom, which is the lethal dose. Amatoxin blocks the replication of DNA, which leads to cell death. This can affect cells that replicate frequently, such as kidneys, livers, and eventually, the central nervous system. It can also cause the loss of muscle contraction and liver failure. Despite the severe and dangerous symptoms, amatoxin poisoning is treatable given quick, professional care. 
Mushrooms have also been found to have evolved toxicity independently from each other. Researchers have found that different mushroom species share the same type of amatoxin called amanitin. They specifically looked at three of the deadliest species, Amanita, Galerina, and Lepiota. Through genome sequencing, a scientific process that determines the DNA sequence of an organism’s genome, closely related mushrooms obtained genetic information via horizontal gene transfer. Once assimilated, it can then be passed down to an offspring. The researchers also concluded that there is “an unknown ancestral fungal donor,” that allowed for horizontal gene transfer.
Mushroom toxins have appeared and disappeared many times throughout their evolutionary history. Many scientists believe that the toxins evolved in mushrooms are used to deter predation, either from fungivores or mammals. If mushrooms are consumed, it can negatively affect their ability to disperse spores, survive, and reproduce. Snails and insects are fungivores and many have learned or evolved to avoid eating poisonous mushrooms. However, it is believed that mammals pose a higher threat to mushrooms than fungivores, as larger body sizes mean they are more capable of eating an entire fungus in one sitting.
Some phenotypes, or observable characteristics, may co-occur with toxicity, and therefore act as a warning signal. The first potential warning sign is aposematism, which is an adaptation that warns off predators based on a physical trait of an organism. In this case, the researchers were interested in observing whether the color of a mushroom deters predators. This would suggest that toxic mushrooms are of different colors than non-poisonous ones. The visual cue of some colors should be enough for predators to know not to consume the mushroom. The second possible warning sign is olfactory aposematism, a similar concept, but instead of focusing on color, the odor of the mushroom would be what deters predation. This would again indicate that poisonous mushrooms would emit a different odor than non-poisonous ones. Alternatively, is the ability of organisms to learn from other organisms. This would suggest that avoidance of toxic mushrooms is a learned behavior. Organisms may avoid toxic mushrooms if they observed other organisms of the same species consume the fungus. Learned behavior is when an organism learns how to behave based on previous experiences. Some researchers believe that if an organism got sick or observed another organism get sick from consuming a poisonous mushroom, then they would know not to continue consuming it for fear of getting sick again.
An analysis of 245 North American mushroom species and 265 from Europe, revealed 21.2% of the North American species and 12.1% of the European ones as poisonous. After collecting this information, and using a neural network to classify all of the mushrooms based on color and odor, the researchers concluded that there was no correlation between cap color and mushrooms containing toxins. The cap is the top, rounded part of a mushroom and comes in different colors. This proposes that the cap color does not act as a warning sign to deter predators, providing no evidence that poisonous mushrooms may not signal their toxicity through visual or chemical traits. The three deadly mushrooms listed above, Amanita, Galerina, and Lepiota, are all of different colors, consisting of reds, yellows, browns, and whites. A possible theory as to why color is not a factor in determining whether a mushroom is poisonous is the fact that many of its predators are nocturnal and have poor vision. Therefore, viewing the different colors is difficult, and