Mushrooms are common throughout the United States, especially in regions that experience a lot of rain and cool temperatures. In fact, around 10,000 species of mushrooms can be found throughout North America, according to Frank Hyman, a mushroom hunter in Durham, NC, and the author of How to Forage for Mushrooms Without Dying: An Absolute Beginner’s Guide.
“Within that number, approximately 110 species are sickeners or killers,” Hyman says. “So, about one percent of mushrooms will either send you running for the toilet or to the ER. The good news is that unlike in the movies, you don’t fall down dead after a bite or two.”
One of the deadliest species of mushroom is Amanita phalloides, commonly known as the death cap mushroom. It can cause significant symptoms within just a few hours of ingestion, and has up to 70 percent mortality rate among dogs that consume it, says Adesola Odunayo, DVM, MS, DACVECC, professor of Emergency and Critical Care at the University of Florida (UF) College of Veterinary Medicine in Gainesville.
“Most mushroom species are benign or may cause mild gastrointestinal signs, but the death cap mushroom largely results in liver failure, which ultimately leads to the death of the patient,” Dr. Odunayo says.
Case in point
Reports of Amanita intoxication among dogs are relatively uncommon, but a 2022 case in California resulted in a side effect so unusual it was reported in the journal Veterinary Sciences.1 It involved a 10-year-old female Labrador retriever named Sadie, owned by Eleanor and Gary Gardner of Atherton, CA. Sadie fell ill after consuming a death cap mushroom while playing outside, though her condition was not diagnosed until three days after she started presenting symptoms, which included vomiting, loss of appetite, urinary retention, and loss of function in her hind legs.
Sadie was eventually seen by a team, including Jonathan Dear, DVM, MAS, DACVIM (SAIM), associate professor of Clinical Small Animal Internal Medicine at the University of California (UC) Davis School of Veterinary Medicine. A rapid-detection urine test for Amanita toxicity confirmed the diagnosis, and Dr. Dear and his team began treatment for liver failure and other symptoms.
“The liver helps maintain blood sugar levels, and Sadie’s levels were low, so we put her on dextrose to support that,” says Dear. “Her clotting times were really high, meaning she wasn’t coagulating properly, so we gave her vitamin K. We also gave her acetyl cysteine to help reduce the risk of oxidative injury in the liver, which can occur when the liver starts to shut down. In addition, we gave Sadie anti-nausea drugs, and put her on fluids to treat her dehydration. We took it day by day to give her body the opportunity to get through it.”
Dealing with another diagnosis
Sadie recovered well from her mushroom encounter, but a previously unseen side effect presented itself about 10 days later: Addison’s disease. “This was very much a surprise,” says Dear. “At her two-week recheck, Sadie wasn’t quite completely herself, but she was significantly improved. About a month after her hospitalization, we noticed something else going on with her because she looked like a dog with Addison’s disease, which had not been previously reported in the veterinary literature. Ours is the first report of this happening to a dog after Amanita intoxication.”
Sadie was diagnosed with classic Addison’s disease, which meant her adrenal glands were not producing the hormones necessary to regulate blood pressure and electrolytes. She currently receives daily prednisone, plus a monthly shot of another form of steroid to help regulate her electrolytes.
The relationship between Amanita intoxication and the development of Addison’s disease is poorly understood. “We know that the liver is affected by Amanita phalloides, but we don’t know if the adrenal glands are also affected in dogs,” Dear says. “We started looking at other species and found reports suggesting Amanita intoxication can affect the adrenal glands in rodents. However, the only way to know if this was the case with Sadie would be to biopsy her adrenal glands, which would be very invasive, risky, and would have no medical value for her. Our hypothesis is Amanita did something similar to Sadie, or that something else happened to her adrenal glands specifically.”
What they found out
Sadie’s story should be a wakeup call to community practitioners for whom mushroom poisoning may be a diagnostic outlier and a warning to all dog owners.
Amanita phalloides are hepatotoxic, but other mushrooms may affect the body differently. Mushrooms that are neurotoxic, for example, include psilocybin, hydrazine and isoxazole mushrooms, reports the American Society for the Prevention of Cruelty to Animals (ASPCA). Symptoms commonly present within 30 to 90 minutes after ingestion. With hydrazine mushrooms, neurological symptoms include weakness, ataxia, tremors and seizures, and gastrointestinal distress. These species of mushroom may also cause hemolysis and methemoglobinemia. Isoxazole mushrooms are also known to cause ataxia, as well as disorientation, vocalization, gastrointestinal distress, and tremors and seizures.
Gastrointestinal symptoms are common following the ingestion of numerous species of mushroom and can range from mild to severe. The muscarinic mushroom is among those resulting in severe gastrointestinal distress, including vomiting and diarrhea that may result in hypovolemia. This species of mushroom may also cause bradycardia and classic SLUDGE signs in dogs: salivation, lacrimation, urination, defecation/diarrhea, gastrointestinal upset, and emesis.
Mushroom poisoning poses a constant threat because dogs are often indiscriminate about what they eat when outdoors. “People engage in a similar behavior when they go mushroom foraging,” Odunayo says. “Some people may think they know what they’re doing but end up eating death cap mushrooms and getting sick. You rarely see mushroom poisoning in cats because they are more discriminate in what they put in their mouths. Dogs just find mushrooms attractive.”
A learning experience
There are several clinical takeaways from Sadie’s case, Dear says. “One of the important things to keep in mind is liver failure and Addison’s disease can look very similar on lab work,” he explains. “One of my biggest takeaways was that if a dog survives Amanita intoxication and the lab work looks like the patient is kind of slipping backward a little bit, we need to keep an open mind that it could be Addison’s disease.
“Another thing I think is important to keep in mind is when we talk to owners about prognosis and the cost of treatment, we need to give them a concise but comprehensible outlook as to what might happen. A dog with Addison’s disease can live a very normal life but will need ongoing care, and owners need to commit to that care.”
Sadie’s owner, Eleanor Gardner, encourages all dog owners to be aware of mushrooms and how dangerous they can be to their pets. “If you see one in your yard, pull it up, and put it in the garbage,” she says. “I also encourage dog owners to be aware of the symptoms of mushroom poisoning, and to take their pets to the veterinarian right away if they suspect their dog has eaten a poisonous mushroom. When Sadie got sick, mushrooms weren’t even on my radar.”
Further, do not assume you can tell a poisonous mushroom from one that is safe to eat. “There are no simple, conclusive indicators of toxicity–none,” says
Hyman, who in the past, had a lucrative side gig selling edible wild mushrooms to area restaurants. “Bottom line–don’t eat any mushrooms unless you can identify them with 100 percent certainty. It’s always better to forget it than regret it.”
Hyman also advises dog owners to train their pets to stay away from any mushrooms they may encounter when outdoors. “Even experienced mushroom hunters won’t know every species they run across, so dog owners should assume all are potentially poisonous to their pet,” he warns.
Don Vaughan is an award-winning writer who frequently writes about veterinary-related topics.