Mushrooms are the fleshy fruiting bodies of fungi. They typically shoot up from growing vegetative (mycelium) portions, and they contain spores as reproductive units. Fungi lack chlorophyll; their nutritional requirements are met by using organic material from saprophytic, parasitic, or mycorrhizal life cycles.
Exposure is by ingestion. Dogs are particularly susceptible to mushroom toxicosis because of their indiscriminate eating habits and a tendency to roam. Although many mushrooms are edible and safe, some contain toxins (eg, cyclopeptides, gyromitrin, orellanine, muscarine, ibotenic acid and muscimol, and psilocybin as well as unknown toxins) that, on ingestion and absorption, result in mild to severe illness and even death. The mushroom species most frequently implicated in human and animal mushroom fatalities globally is Amanita phalloides.
Most Amanita species are typically identified by their physical characteristics: veil (ring or skirt) or partial veil (annulus) around the upper part of the stem, smooth yellowish-green to yellowish-brown cap or pileus, white gills (spore-bearing structure under surface of pileus), spores (reproductive structure—white to black and other shades of color), stipe or stalk (cap support), volva (cup-like structure at the base of the stem), and mycelium. Other characteristics helpful in the identification of some poisonous mushrooms are listed in . Visual identification can be difficult, even for experienced mycologists, especially considering that the appearance of the mushrooms can be distorted by mastication, gastric secretions, or orally administered treatments such as activated charcoal. For a spore print and spore identification, a mycologist must be consulted. In cases of human poisoning, PCR assays have been used to identify ingested mushrooms when visual identification is inconclusive or impossible.
The latent period between mushroom ingestion and observed clinical signs in exposed animals largely dictates the prognosis. A long delay of 6–12 hours often occurs with exposure to amanitins, with often fatal outcomes ( ). However, short latent periods do not necessarily indicate a favorable prognosis, in that the animal may have ingested a combination of nonlethal and lethal mushroom species growing in the same location. Generally, for mushroom species that produce clinical signs ≤3 hours after ingestion, effects are self-limiting and not life-threatening, whereas those that produce clinical signs>6 hours after ingestion are life-threatening.
The rapid emergence of mushrooms and their short lifespan within the environment, coupled with the indiscriminate eating habits of many animals, creates diagnostic challenges. History, time after ingestion at which clinical signs occur, and, when possible, mushroom identification determine the treatment approach and prognosis. Establishing the time of ingestion may be difficult or impossible. With no proven antidotes to treat mushroom toxicosis, treatment is primarily directed at decontamination and intensive supportive care.