Mushroom toxins are challenging to deal with: They can be hard to properly identify, their range of toxicity goes from minor to deadly, they appear suddenly—generally in wet, warm weather like spring and fall—and many animals can get to them easily.
Many species of mushrooms exist, but knowing the specific name is not always the most important aspect. Mushrooms can be lumped into four categories to help you remember them: hepatotoxic, neurotoxic, gastrointestinal, and nephrotoxic.
With common names like death cap (Amanita phalloides) and destroying angel (Amanita bisporigera and Amanita ocreata) it’s easy to remember these mushrooms.
Amanitins are responsible for the acute liver failure associated with these mushrooms. Onset of signs can be delayed 6 to 12 hours, giving owners a false sense of security. Once pets start showing signs of gastrointestinal distress, liver failure can quickly follow. Death may occur one to two days after exposure in severe cases.
These mushrooms can be found throughout North America and are commonly found in the Pacific Northwest, parts of California, and the northeastern part of the United States.
Three main groups of mushrooms will cause neurological signs: psilocybin or “magic” mushrooms, hydrazines, and isoxazole mushrooms. Onset of signs with these mushrooms is going to be more rapid—as soon as 30-90 minutes is common and less than six hours is likely.
Gyromitrin is the primary compound of concern with hydrazine mushrooms. While neurological signs can be seen—weakness, ataxia, tremors, and seizures—gastrointestinal signs are more common. These mushrooms may also be associated with a hemolysis, methemoglobinemia, and, rarely, renal and hepatic involvement.
Isoxazole mushrooms will cause gastrointestinal signs along with ataxia, disorientation, hallucinations, vocalization, alternating lethargy and agitation, as well as tremors and seizures. Signs typically resolve within 12-24 hours.
The group of mushrooms causing gastrointestinal signs is relatively large, with signs that may be mild to severe. The onset of signs will be on the rapid side, as soon as 15 minutes and typically less than six hours after exposure.
One type of mushroom to note in this group is the muscarinic mushrooms. In addition to potentially significant vomiting and diarrhea leading to hypovolemia, these mushrooms will also cause bradycardia, bronchial secretions, and classic SLUDDE signs.
Nephrotoxic mushrooms, Cortinarius spp, are more elusive. While reports of toxicity exist in humans, most of those in Europe, there are no reports of unintentional poisonings in dogs or cats.
Like hepatotoxic mushrooms, onset of signs can be delayed (typically 12 hours but can be 3-8 days or longer). Typical signs include polydipsia and polyuria, vomiting, nausea, and dehydration.
Due to the potential seriousness of a mushroom exposure in a pet or rapid onset of signs, worrying about identifying the mushroom should take a back seat to decontamination or symptomatic care.
Once the pet is stable—and if mushrooms are available for identification—consider contacting a mycologist at a local college or university or the North American Mycological Association (www.namyco.org). The website is a good source of information and also provides a list of volunteers across the country who may help with mushroom identification. There are also Facebook groups run by mycologists that can be helpful for identification. Do NOT try to identify a mushroom just by looking at photos.