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Overview of Poisonous Mushrooms

By Cecil F. Brownie, DVM, PhD, DABVT, DABFE, DABFM, FACFEI, Emeritus Professor, College of Veterinary Medicine, North Carolina State University

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 they 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. Although 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/absorption 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 Physical Characteristics of Common Poisonous Mushrooms.

Physical Characteristics of Common Poisonous Mushrooms

Genus and Species

Color of Cap/Spores

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 California

A pantherina

White with whitish patches; dark to yellow-brown/white at margin

Ground under conifers (Douglas fir)

Autumn/winter: June, Sept–Oct, Nov–Feb (California)

Rocky Mountains/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

Massachusetts to Virginia west to Ohio; Pacific northwest to California

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 California, common in Denver, reported in New York and New Jersey

Clitocybe spp

White/white

Ground

Perennial

Widespread in North America

Cortinarius orellanus

Orange/brown

Ground under conifers

July–Aug; Sept–Oct (Rocky Mountains)

Widespread in North America

Galerina spp

Brown-orange/rust-brown

Ground-wood, well-decayed conifers and logs

Autumn/spring: Oct–Nov, May–June

Throughout North America

Gyromitra esculenta

Brown-rust/yellow to buff

Ground under conifers

Spring: April–early June

Throughout North America

Inocybe spp

Brown/bright rust/orange-brown or dull gray-brown

Ground

Autumn: May–Nov

Widespread in North America

Lepiota spp

White with brownish scales/white

Ground conifers, grass, leaf litter, oak and mixed woods

July–Oct (Michigan, Ohio); July–Nov (Florida); Nov–Feb (California)

Throughout North America

Paxillus involutus

Brown/sienna (clay-brown)

Ground: single/numerous on wood in mixed woods

July–Nov

Widespread in North America

Psilocybe cubensis

Brown/lilac brown to dark purple brown

Ground/wood/dung (cattle, horses)

Year round

Gulf Coast

Russula emetica

Reddish/white to yellowish white/whitish

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 mushroom ingestion and observed clinical signs in exposed animals largely dictates the prognosis. A long delay time is synonymous with fatality ( Poisonous Mushrooms: Onset of Action and Organs Targeted). However, short latent periods do not always indicate survival, because the animal may have ingested a combination of non-lethal/lethal mushroom species growing in the same location (dilution effect, or dose determines toxicity). 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.

Poisonous Mushrooms: Onset of Action and Organs Targeted

Mushrooms

Toxin

Onset Time

Organ/System

Latent Period >6 hr After 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 After 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 after ingestion at which clinical signs are seen determine the treatment approach and prognosis. Establishing the time of ingestion may be difficult to impossible. With no proven antidotes to treat mushroom poisonings, treatment is primarily directed at decontamination, mushroom identification when possible, and intensive supportive care.

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