Mushrooms are the fruiting bodies of a variety of fleshy fungi that are found worldwide. They typically appear suddenly from growing vegetative (mycelium) portions, and contain spores as reproductive units. Fungi lack chlorophyll; their nutritional requirements are met by utilizing organic material from a saprophytic, parasitic, and/or mycorrhizal life cycle.

Exposure is by ingestion. While most mushrooms are edible and safe, a few contain diverse secondary metabolites (cyclopeptides, monomethylhydrazine, orelline/orellanin, muscarine, ibotenic acid and muscimol, psilocybin, and unknowns) that on ingestion result in mild to severe illness and even death. The mushroom species most frequently implicated in human/animal mushroom fatalities globally is Amanita phalloides. Most Amanita species are typically identified by their physical characteristics—veil (universal/partial), cap or pileus (with scales—remnants of universal veil), lamellae (gill-like, spore-bearing structure under surface of pileus), spores (reproductive structure—white to black and other shades of color), stipe/stalk (cap support), annulus or ring (remnant of partial veil on stipe below pileus), volva (remnant of universal veil at base of bulb), and mycelium. Other characteristics helpful in the identification of some poisonous mushrooms are listed in see Poisonous Mushrooms: Physical Characteristics of Common Poisonous Mushrooms.

Amanita phalloides

Table 1
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Physical Characteristics of Common Poisonous Mushrooms Name (Genus/Species) Cap/Spores Color Habitat Season Range Amanita muscaria Red-tan to yellow/orange/ white Ground-pine, spruce, birch, poplar and oak trees Autumn/ winter: June–Nov Widespread, common in East and Calif A pantherina White with whitish patches; dark to yellow-brown at margin Ground under conifers (Douglas fir) Autumn/ winter: June, Sept–Oct Nov–Feb (Calif) Rocky Mtns/West coast; rare in East A phalloides Yellow/green or green/white Ground under conifers, hardwoods; junipers and oaks Autumn: late Sept–Nov Nov–Jan Mass. to Virginia west to Ohio; Pacific NW to Calif A virosa White/white Ground; mixed woods; grass, near trees Autumn: late June–early Nov North America Chlorophyllum molybdites White/green or grayish white Lawn, pastures, meadows, fairy rings Summer: Aug–Sept Florida to Calif, common in Denver. Reported in NY and NJ Clitocybe spp White/white Ground Perennial Widespread in North America Cortinarius orellanus Orange/brown Ground under conifers July–Aug; Sept–Oct (Rocky Mtns) North Widespread in North America Galerina spp Brown/rust-brown Ground-wood, well decayed conifers and logs Autumn/spring: Oct–Nov May–June Throughout North America Gyromitra esculenta Brown-rust Ground under conifers Spring: April–early June Throughout North America Inocybe spp Brown/bright rust/orange-brown or gray-brown Ground Autumn: May–Nov Widespread in North America Lepiota spp White with brownish scales Ground conifers, grass, leaf litter, oak and mixed woods July–Oct (MI; OH); July–Nov (FL); Nov–Feb (Calif) Throughout North America Paxillus involutus Brown Ground: single/numerous on wood in mixed woods July–Nov Widespread in North America Psilocybe cubensis Brown/purple brown Ground/wood/dung (cattle, horses) Year round Gulf Coast Russula emetica Reddish/white to yellowish white Single/group; on sphagnum moss, rarely on very rotten wood, conifers or mixed woods July–Sept Widespread in North America Physical Characteristics of Common Poisonous Mushrooms Name (Genus/Species) Cap/Spores Color Habitat Season Range Amanita muscaria Red-tan to yellow/orange/ white Ground-pine, spruce, birch, poplar and oak trees Autumn/ winter: June–Nov Widespread, common in East and Calif A pantherina White with whitish patches; dark to yellow-brown at margin Ground under conifers (Douglas fir) Autumn/ winter: June, Sept–Oct Nov–Feb (Calif) Rocky Mtns/West coast; rare in East A phalloides Yellow/green or green/white Ground under conifers, hardwoods; junipers and oaks Autumn: late Sept–Nov Nov–Jan Mass. to Virginia west to Ohio; Pacific NW to Calif A virosa White/white Ground; mixed woods; grass, near trees Autumn: late June–early Nov North America Chlorophyllum molybdites White/green or grayish white Lawn, pastures, meadows, fairy rings Summer: Aug–Sept Florida to Calif, common in Denver. Reported in NY and NJ Clitocybe spp White/white Ground Perennial Widespread in North America Cortinarius orellanus Orange/brown Ground under conifers July–Aug; Sept–Oct (Rocky Mtns) North Widespread in North America Galerina spp Brown/rust-brown Ground-wood, well decayed conifers and logs Autumn/spring: Oct–Nov May–June Throughout North America Gyromitra esculenta Brown-rust Ground under conifers Spring: April–early June Throughout North America Inocybe spp Brown/bright rust/orange-brown or gray-brown Ground Autumn: May–Nov Widespread in North America Lepiota spp White with brownish scales Ground conifers, grass, leaf litter, oak and mixed woods July–Oct (MI; OH); July–Nov (FL); Nov–Feb (Calif) Throughout North America Paxillus involutus Brown Ground: single/numerous on wood in mixed woods July–Nov Widespread in North America Psilocybe cubensis Brown/purple brown Ground/wood/dung (cattle, horses) Year round Gulf Coast Russula emetica Reddish/white to yellowish white Single/group; on sphagnum moss, rarely on very rotten wood, conifers or mixed woods July–Sept Widespread in North America

The time lapse (latent period) between ingestion and observed clinical signs in exposed animals by and large dictates the prognosis. Long delay time is synonymous with fatality (see Poisonous Mushrooms: Poisonous Mushrooms: Onset of Action and Organs Targeted). Short latent periods do not always indicate non-lethality, because the animal may have ingested a combination of mushroom species. In mushroom species with clinical signs that appear <3 hr after ingestion, effects are generally self-limiting and not life-threatening. Those with clinical signs that appear >6 hr after ingestion are life-threatening.

Table 2
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Poisonous Mushrooms: Onset of Action and Organs Targeted Mushrooms Toxin Onset Time Organ/System Latent Period >6 hr Post-ingestion; Life-threatening Amanita phalloides; A virosa Cyclopeptides, α and β amanitins, phallotoxins, virotoxins 6–24 hr, rarely >24 hr Primarily liver, kidney secondary Conocybe filaris α and β amanitins 6–14 hr, rarely >24 hr Primarily liver Cortinarius gentilis Orellanin, orelline 3–14 days (days/weeks) Primarily renala Galerina autumnalis; G venenata α and β amanitins 6–14 hr, rarely >24 hr Primarily liver Gyromitra esculenta Monomethylhydrazine 6–24 hr CNS Lepiota spp α and β amanitins 6–14 hr, rarely >24 hr Primarily liver Latent Period £3 hr Post-ingestion; not Life-threatening Amanita muscaria; A pantherina Isoxazoles: ibotenic acid muscimol 30 min–2 hr; recovery 4–24 hr CNS Chlorophyllum molybdites Unknown 30 min–3 hr; recovery 1–2 days GI Clitocybe dealbata; Clitocybe spp; Inocybe spp Muscarine 30 min–2 hr; recovery 6–24 hr Autonomic nervous system Paxillus involutus Unknown 1–3 hr; recovery 2–4 days Immune system Psilocybe spp; Conocybe smithii; Gymnopilus spectabilis; Panaeolus subbalteatus Psilocybin and psilocin 30–60 min; rarely 6 hr CNS Russula emetica Unknown 30 min–3 hr; recovery 1–2 days GI a No reported veterinary cases Poisonous Mushrooms: Onset of Action and Organs Targeted Mushrooms Toxin Onset Time Organ/System Latent Period >6 hr Post-ingestion; Life-threatening Amanita phalloides; A virosa Cyclopeptides, α and β amanitins, phallotoxins, virotoxins 6–24 hr, rarely >24 hr Primarily liver, kidney secondary Conocybe filaris α and β amanitins 6–14 hr, rarely >24 hr Primarily liver Cortinarius gentilis Orellanin, orelline 3–14 days (days/weeks) Primarily renala Galerina autumnalis; G venenata α and β amanitins 6–14 hr, rarely >24 hr Primarily liver Gyromitra esculenta Monomethylhydrazine 6–24 hr CNS Lepiota spp α and β amanitins 6–14 hr, rarely >24 hr Primarily liver Latent Period £3 hr Post-ingestion; not Life-threatening Amanita muscaria; A pantherina Isoxazoles: ibotenic acid muscimol 30 min–2 hr; recovery 4–24 hr CNS Chlorophyllum molybdites Unknown 30 min–3 hr; recovery 1–2 days GI Clitocybe dealbata; Clitocybe spp; Inocybe spp Muscarine 30 min–2 hr; recovery 6–24 hr Autonomic nervous system Paxillus involutus Unknown 1–3 hr; recovery 2–4 days Immune system Psilocybe spp; Conocybe smithii; Gymnopilus spectabilis; Panaeolus subbalteatus Psilocybin and psilocin 30–60 min; rarely 6 hr CNS Russula emetica Unknown 30 min–3 hr; recovery 1–2 days GI a No reported veterinary cases

The sudden appearance of mushrooms and their short lifespan within the environment, coupled with the indiscriminate eating habits of many animals, creates diagnostic challenges. History and time post-ingestion at which clinical signs are observed determine the treatment approach and prognosis. Establishing the time of ingestion may be difficult to impossible. With no proven antidotes for treating mushroom poisonings, treatment is primarily directed at decontamination, mushroom identification when possible, and intensive supportive care.

Last full review/revision March 2012 by Cecil F. Brownie, DVM, PhD, DABVT, DABT, DABFE, DABFM, FACFEI