Toxic Mushroom Ingestions

Chapter 65 Toxic Mushroom Ingestions

For online-only figures, please go to image

Mushrooms are often considered the vermin of the vegetable world, likened to snakes, slugs, and worms. Some are regarded as mystical and others as delicacies. The locations of tasty morels are passed on from generation to generation, closely guarded from strangers. Each autumn and spring, foragers scour the woods for known delicacies and new ones untried. Some mushroom foragers search for “little brown mushrooms,” not for their taste, but to evoke hallucinations.

Eating unidentified or misidentified species can be dangerous. In the vast majority of toxic ingestions (perhaps up to 95%), the mushroom was incorrectly identified. More than 40,000 species of fungi are currently described, with a few thousand new ones added each year. Only a few species are toxic.

The fungi kingdom contains molds, smuts, rusts, mildews, yeasts, and mushrooms, which are different from plants because they lack chlorophyll. Yeasts are single-cell organisms that divide using budding. Mold is any fungus that grows with thread-like connections and a fuzzy appearance. Mildew, rust, and smut are all fungi related to mushrooms and break down vegetable matter, leaving behind a white, red, or black powder, respectively. Toadstool is often used to describe toxic mushrooms. This chapter differentiates toxic mushrooms by their toxins and scientific names.

The body of a fungus is a dense network of branching filaments, or hyphae. The mushroom is the fruiting body of the fungus, containing the spores. The hyphae and mycelia generally occur in an underground network supporting the visible mushroom. Mushrooms often grow in large rings radiating from a central network of mycelia. In the past, these “fairy rings” were thought to have mythical influence (Figure 65-1, online). Recently a fairy ring in northeast Oregon has been found to occupy an area over 10 km2 (3.9 miles2). This ring is thought to be between 2000 and 8000 years old, making it the oldest and largest single organism on the planet. Fungi are largely saprophytic (i.e., growing on decaying vegetable matter), involved with the decomposition of rotting materials, usually wood. They can also be parasitic (i.e., living on another living organism, injuring the host) or symbiotic (i.e., living together with each benefiting). Some emerge only after significant environmental changes, such as the large quantity of morels that may be found where a forest fire has recently occurred.

As a mushroom emerges from the ground, it is covered with a membrane or veil (Figure 65-2). As the mushroom grows (Figure 65-3), the membrane breaks, leaving residual marks known as warts on the cap of the mushroom (Figure 65-4). These warts may remain firmly attached to the mushroom or may remain as only residual spots, depending on the species of mushroom and environmental conditions. The emerging cap takes on a shape consistent with the specific species, ranging from cylindric to convex to funnel shaped.

Gills located under the cap contain the spore-producing bodies. Some gills are covered with a second membrane or partial veil, which later pulls away to form an annulus, or ring, midway down the stalk of the mushroom. Gills may be attached firmly to the stalk, sometimes running down the stalk, or only to the cap itself (free gills) (Figure 65-5). Attachment of the gills is an important aid to identification of some poisonous mushrooms, such as Amanita phalloides (Figure 65-6).

The stalk (stipe) begins at the cap and ends either underground or in a cup (vulva) (Figure 65-7). A vulva at or just below ground level often is seen in a poisonous species. The stipe is generally located in the center of the cap and may or may not be tapered. The stipes of many poisonous species enlarge below the cap, ending in a bulb. The stipe may have a ringed membrane as evidence that the partial veil formerly protected the gills (Figure 65-8). Spores are produced by spore-forming bodies on the gills and expelled into the air after they mature.

Spores vary in size, color, and shape but are usually unicellular. They average 5 to 10 µm in diameter. Spores are useful in identifying mushroom species (Figure 65-9 and Box 65-1). They can be obtained by cutting the stipe of a fresh specimen close to the gills, then laying the cap gill-side down on white paper for a few hours at room temperature. The initial color seen after removal of the gills is used for identification. With drying, the color may fade or change. Additional information about spores can be acquired by staining with Melzer’s reagent (a solution of iodine and chloral hydrate). Spores that stain blue are called amyloid, indicating the presence of starch (Figure 65-10). This technique may be particularly useful in spore identification from gastric aspirates. Spores of Amanita species are amyloid. Thin-layer chromatography of spores available from a mycology laboratory, mushroom farm, or botany department is a more accurate aid to identification.

There are many species of mushrooms, including several that are hunted, that have no caps, gills, or stipes. They have developed alternative methods of releasing their spores. The “puffball” mushrooms are well known by the cloud of spores they release through a pore on the top surface of their spherical fruiting bodies (Figure 65-11). This spore release occurs when the spores are mature and may be initiated by a falling branch, errant placement of a deer’s hoof, or the squeezing fingers of a curious child.

Mushrooms are composed of approximately 90% water and 3% proteins and other nitrogen-containing compounds. The remainder is largely carbohydrate, fat, and a few vitamins. Nutritionally unimpressive, mushrooms are consumed in great quantities, primarily for their taste and texture. Wild mushrooms have the additional allure of being free. This is changing in many parts of the northwestern United States, where some species of mushroom have become so profitable that pickers have had to buy commercial permits, and gun battles have erupted over territorial disputes.

Of the many varieties of wild mushrooms, few are deadly or cause serious illness. All mushrooms, including toxic ones, are safe to handle without gloves; however, hand washing after handling is strongly recommended. Many experts will even bite off and chew a small piece of mushroom to gather taste information before spitting it out. As in wine tasting, a thorough rinsing is recommended after each taste.

Many immigrants fail to realize that the nontoxic mushrooms from their native lands have toxic look-alikes in America. This is particularly true of Southeast Asian immigrants, who are attracted to the large Amanita species. Entire families have been poisoned, with many fatalities. The Russian roulette played by mushroom foragers is statistically safe. Some self-proclaimed experts are simply lucky; occasionally, they are not.

Nontoxic Mushrooms

The most common commercially available mushroom in the United States is Agaricus bisporus (Figure 65-12). It is cultivated in abandoned mine shafts and caves. This small white mushroom with dark gills is often picked before the gills are fully exposed. Although the mushroom is considered nontoxic, hypersensitivity reactions and gastrointestinal symptoms have been reported. In some parts of the United States, close relatives of this common mushroom account for the largest percentage of toxic mushroom cases. Most often it causes gastrointestinal disturbance. Agaricus species may be confused with the deadly Amanita species (Figure 65-13). The popular portobello mushroom is a type of A. bisporus. A. bisporus can also be found in the wild.

Nontoxic mushrooms may carry environmental toxins, such as heavy metals and pesticides. Mushrooms with high lead concentrations have been gathered near highways.34 High mercury concentrations are found in mushrooms from industrial sites.87 Many mushrooms fruit among cultivated plants and may contain toxic levels of pesticides. Human toxicity has not been reported.

Fungi may cause allergic reactions. Molds that grow in damp locations in buildings have been suspected to cause a variety of patient complaints. They are one cause of the “sick building” syndrome that has resulted in some structures being vacated or demolished when the problem could not be remedied by conventional methods. Acute anaphylaxis from mushroom ingestion is rare, despite the presence of haptens capable of inciting an allergic response.57 More often, symptoms develop from inhalation of spores.74 Victims may present with anaphylaxis or, more commonly, with chronic hypersensitivity pneumonitis. Hypersensitivity reactions are described in workers exposed to cultivation of A. bisporus (the most popular commercially grown mushroom in America)63 and shiitake (Lentinus edodes), the popular Japanese mushroom (Figure 65-14).91 Asthma symptoms developed in nearly 10% of shiitake-exposed workers. In one study, all workers had positive skin and inhalation challenge tests.102 Spore counts correlate with asthma symptoms.

Gastroenteric symptoms after ingestion of mushrooms may not be due to toxins. Bacterial food poisoning may occur in foods that coincidentally contain mushrooms. Small bowel obstruction occurred in a person who consumed 500 g of the edible mushroom Cantharellus cibarius (chanterelle) (Figures 65-15 and 65-16; Figure 65-15, online).36 This was largely a result of poor mastication, because entire mushrooms were recovered from the victim’s intestines.

Most wild mushrooms are nontoxic, and many are delicious. Morels (Morchella esculenta or deliciosa (Figure 65-17) are highly prized delicacies. Chanterelles (C. cibarius) (see Figures 65-15 and 65-16; Figure 65-15, online) and several species of Boletus (Figures 65-18 and 65-19; Figure 65-18, online) are particularly tasty. The chicken mushroom (Laetiporus sulphureus) (Figures 65-20 and 65-21; Figure 65-20, online) is often used in place of chicken in Chinese dishes. Extracts of the shiitake mushroom, L. edodes, may have antimalarial properties.121

Gastrointestinal Toxins

Most toxic mushrooms fall into the group of gastrointestinal irritants. This large, heterogeneous group of mushrooms causes gastrointestinal distress, consisting of nausea, vomiting, and diarrhea, beginning 1 to 2 hours after ingestion and resolving in 6 to 12 hours. Even A. bisporus, the common cultivated mushroom, may cause brief gastroenteritis in some individuals.103 The mechanism is unknown.

Causative Mushrooms

A large number of unrelated mushrooms cause gastrointestinal symptoms with varying host responses (Box 65-4). Chlorophyllum molybdites (also known as Lepiota morganii) (Figure 65-22) is the most frequently ingested toxic mushroom in America. Most persons who ingest C. molybdites confuse it with A. bisporus, which it closely resembles. The common name for C. molybdites, green-spored parasol, describes the characteristics of this summer mushroom. The whitish cap is 10 to 40 cm (3.9 to 15.7 inches), initially smooth and round, and becomes convex with maturity. Tan or brown warts may be present. The gills are free from the stalk, initially white to yellow, and become green with maturity. The stalk is 5 to 25 cm (2 to 9.8 inches) long, smooth, and white. The ring is generally brown on the underside. Spores are green. The mushroom is common in most of eastern and southern North America and in California. In southern California, it is a common lawn mushroom.

BOX 65-4 Mushrooms Reported to Cause Gastrointestinal Irritation

Another common mushroom causing gastrointestinal symptoms is the jack-o’-lantern (see Figure 65-44). Its botanical classification is not completely settled. Most commonly, it is referred to as Omphalotus illudens (see Figure 65-44), Omphalotus olearius, or Omphalotus olivascens (see Figure 65-45). The mushroom is a bright orange-yellow mushroom with sharp-edged gills and often grows in clusters at the base of stumps or on buried roots of deciduous trees. The cap is 4 to 16 cm (1.6 to 6.3 inches) in diameter on a stalk that is 4 to 20 cm (1.6 to 7.9 inches) long. Gills are olive to orange, with white to yellow spores. The mushroom shows characteristic luminescence lasting 40 to 50 hours after collection. Members of this family are found in both eastern and western North America, generally in autumn and early spring. They may be mistaken for the edible species C. cibarius (see Figure 65-15, online). Some European reports have documented hepatic impairment and muscarinic effect following ingestion.110 It is not clear whether the mushroom and its toxins are the same on both sides of the Atlantic.

Although the genus Amanita is most famous for its deadly member A. phalloides (see Figure 65-6), the genus also contains tasty nontoxic mushrooms (e.g., Amanita caesarea [Figure 65-50], Amanita calyptrata, and Amanita velosa). Several Amanita species cause gastrointestinal symptoms indistinguishable from those caused by jack-o’-lantern mushrooms or C. molybdites (see Figure 65-29, online). Amanita brunnescens (see Figure 65-25) and Amanita flavorubescens (see Figure 65-28) are frequently listed as containing gastrointestinal toxins, although they are occasionally listed as edible. Both have broad yellowish to brown caps (3 to 15 cm [1.2 to 5.9 inches]) with loosely attached warts. The stalks are 3 to 18 cm (1.2 to 7.1 inches) long, enlarging toward the base with a superior ring. A. brunnescens stains reddish brown when bruised. As with most Amanita, these mushrooms are found in summer or fall associated with hardwoods or conifers.

Several members of the genus Agaricus, particularly Agaricus albolutescens, A. silvaticus, and A. xanthodermus (Figure 65-51), can cause gastrointestinal symptoms. They resemble the cultivated mushrooms in grocery stores and are found in meadows and lawns in the summer and autumn. Table 65-1 lists the look-alike toxic and nontoxic mushrooms in this group.

TABLE 65-1 Gastrointestinal Irritant Mushrooms Mistaken for Edible Species

Gastrointestinal Irritant Edible Species
Agaricus Agaricus bisporus
xanthodermus (see Figure 65-24)  
Amanita brunnescens (see Figure 65-25) Amanita flavorubescens (see Figure 65-28)
  Amanita inaurata (Figure 65-52)
Chlorophyllum molybdites (see Figures 65-22 and 65-29; Figure 65-29, online) Lepiota species (Figure 65-53)
Agaricus bisporus (see Figure 65-12)
Pluteus cervinus
Entoloma species (see Figure 65-30)
Entoloma abortivum
Hebeloma crustuliniforme Rozites caperata (Figure 65-54)
Naematoloma fasciculare Armillaria mellea (Figures 65-55 to 65-58)
  Naematoloma sublateritium
  Naematoloma capnoides
Paxillus involutus Lactarius species (Figure 65-59)
Ramaria formosa (see Figure 65-46) Ramaria species
Ramaria gelatinosa  
Scleroderma aurantium Lycoperdon perlatum (Figure 65-60)
Tricholoma pessundatum Cantharellus cibarius (see Figure 65-16)
Omphalotus olearius (see Figure 65-44) Laetiporus sulphureus (see Figure 65-21)
  Armillaria mellea (see Figures 65-55 to 65-58)


Treatment is largely supportive (Box 65-5) and does not depend on the type of mushroom ingested. Intravenous (IV) fluid and electrolytes replacement may be required. In a severe case, an antiemetic such as prochlorperazine, 5 mg IV or 10 mg intramuscularly (IM), may prevent further emesis, although there is no evidence for its use. If patients present within 1 hour of ingestion and vomiting has not occurred, activated charcoal (1 g/kg) without cathartic is given orally or through a nasogastric tube. There is no evidence, however, that its use decreases toxicity. Once vomiting starts, charcoal is likely useless. Although antimotility drugs are often given, there is no evidence that they are effective. Most cases are self-limited.

Care should be taken not to dismiss early gastrointestinal symptoms when several types of unknown mushrooms have been ingested. Individuals may ingest both gastrointestinal irritant mushrooms and mushrooms containing serious toxins. Persons with prolonged gastroenteritis from unidentified mushrooms should be observed for 24 to 48 hours for development of delayed hepatic damage. Special efforts should be made to identify the ingested mushrooms.

Disulfiram-Like Toxins

A fascinating toxicity is caused by some members of the Coprinus genus, known as “inky caps” (Figures 65-61 and 65-62; Figure 65-61, online). Individuals who ingest these mushrooms and subsequently ingest alcohol have symptoms similar to those of an alcohol-disulfiram (Antabuse) reaction.

Causative Mushrooms

Several members of the Coprinus genus may contain disulfiram-like toxins (Box 65-6), but symptoms are most common with Coprinus atramentarius. The mushroom has a 2- to 8-cm (0.8- to 3.1-inch) cylindric cap on a thin 4- to 5-cm (1.6- to 2-inch) stalk. The cap is white or occasionally orange or yellow at the top. The mature cap often develops cracks, which turn up at its margins. The cap blackens as it matures and then liquefies into the “inky cap.” A ring may be present low on the stalk. Spores are black. C. atramentarius grows throughout North America in clusters of three or more in grass or wood debris. It often appears overnight after a rain. Several members of the Coprinus genus, including C. atramentarius, are edible if no alcohol is ingested for the next 72 hours.

Sep 7, 2016 | Posted by in EMERGENCY MEDICINE | Comments Off on Toxic Mushroom Ingestions
Premium Wordpress Themes by UFO Themes