A fungus [plural: fungi] is a plant-like organism that lacks chlorophyll and is usually non-mobile, filamentous and multicellular.
A fungus [plural: fungi] is a plant-like organism that lacks chlorophyll and is usually non-mobile, filamentous and multicellular. Molds and mushrooms are examples of fungi. There are thousands of molds and mushrooms, many containing substances that can cause adverse effects in animals who ingest them. In this section, we will cover the fungi that are most clinically relevant in veterinary medicine.
Mushroom poisoning, or mycetismus, is an infrequently confirmed diagnosis in veterinary medicine. Due to the difficulty of analytically testing for mushroom toxins in biological specimens, actual cases of poisoning in pets may be under diagnosed. Many ingestions go unobserved by anyone and many times it is the presence of pieces/parts of mushrooms in vomitus that alerts the owner to seek help. In addition, there are several categories of mushroom toxins that can elicit very different clinical signs, which can be easily confused with other more commonly recognized diseases.
Among the thousands of mushrooms present in the United States, approximately 50-100 species are toxic. Diagnosis and confirmation of mushroom poisoning in pets is often difficult. Many times the pet is not observed eating the mushroom, but mushrooms are found in the pet's environment. Clinical signs associated with mushroom poisoning are varied, depending on toxin and dose, and are not unique. There are few laboratories that test for the toxins present in mushrooms, and many of the toxins have short half-lives. In addition, mushroom preservation is critical to accurate identification by a mycologist.
As mentioned above, diagnosis of mushroom poisoning is often difficult unless the animal is observed eating the fungus. Finding pieces of mushrooms in the vomitus or stomach contents should certainly make one suspicious of a possible mushroom poisoning if the clinical signs are appropriate. Fecal flotation and direct smears of the feces, or microscopic examination of the gastric contents may reveal spores, which can be helpful to identifying the mushroom. There are many reference books and internet sites that can be used to help identify mushrooms. However, it is best that identification be performed by a highly trained mycologist. Mycologists can be found at colleges and universities, through local/regional mycology clubs, and via the North American Mycological Association [http://www.namyco.org/contact.html]. Once the mushroom is accurately identified, you can determine whether it is toxic or not by accessing numerous textbooks, internet web sites or Poison Control Centers [800.222.1222].
Preservation of the sample is critical due to the high moisture content of mushrooms. Once picked, mushrooms decay quite rapidly, so identification should be performed quickly. If rapid identification is not possible, one can dry the mushroom [let sit at room temperature or place in the oven on a cookie sheet at low temps - 100F]. All specimens, whether fresh or dried, should be placed on a white sheet of paper, then wrapped in wax paper, and placed in an airtight plastic bag or paper bag with a dry paper towel for transport. Taking a picture of the mushroom prior to shipping can be extremely helpful. Information about the mushroom's location [e.g., lawn, garden, woods, mulch pile, etc.] should always accompany the specimen. Making a spore print prior to shipping is also helpful. To make one, cut off the mushroom's stalk close to the base. Place the cap, with the gills or pores facing down, on a piece of white paper [dark paper may be used if the gills are white]. Then cover with a glass. Some mushrooms produce spore prints in a few hours, others take longer. Samples of vomitus and lavage washings for toxicology testing should be frozen.
The majority of recognized cases involve dogs, especially puppies, due to their indiscriminate eating habits. However, all animals are susceptible to mushroom's toxic effects. The mushrooms of toxicological importance in North America are divided into several categories based on the physical effects of the toxin and clinical signs.
Category A includes mushrooms of the genera Amanita, Lepiota and Galerina (less commonly Conocybe and Pholiotina) that contain cyclic peptides (amatoxins, phallotoxins or phalloidins, and virotoxins). These toxins inhibit nuclear RNA polymerase and thereby target protein synthesis. The gastrointestinal tract, kidney and liver are the most significantly impacted tissues. These mushrooms are responsible for the majority of the mushrooms related mortalities seen in pets; a single mushroom can be potentially fatal to an average size dog or cat. The toxins are very heat stable. Initial signs generally appear within 6-12 hours after ingestion and include abdominal pain, vomiting and diarrhea. These signs usually subside after a few hours (sometimes up to 1 or more days) and this apparent improvement may last for several hours, up to 3 days. This is then followed by severe hepatic and renal dysfunction, seizures, and/or a terminal hemolytic event. Common changes include jaundice, hypovolemia, elevated liver enzymes and bile acids, acid-base abnormalities, coagulopathy, hypoglycemia and shock.
Treatment options include early emesis, lavage, activated charcoal and cathartic. Large doses of penicillin G [300,000 to 40,000,000 U/day] and silymarin [1.4-4.2 g/day] have been shown to reduce hepatic uptake of the toxin in the first few hours of exposure. Basic supportive measures may include IV fluid therapy, SAMe, actigall, n-acetylcysteine, vitamin E, correction of acid-base abnormalities, blood and/or plasma transfusions, providing adequate respiratory support, correcting hypothermia and basic palliative care. It is recommended that renal and hepatic function be monitored for up to 72 hours post ingestion. A few laboratories offer amatoxin testing, but the half-life can be short, so not finding it in biological specimens does not rule out exposure.
Category B includes mushrooms from the genus Cortinarius. Poisoning with these mushrooms has rarely been reported in the United States, though it is well documented in Europe. The toxins orelline and orellanine specifically target the gastrointestinal tract and kidney. Initial signs include vomiting and diarrhea, followed later [3-14 days] by signs associated with renal failure [e.g., vomiting, depression, oliguria, isosthenuria, tubular casts]. Treatment involves decontamination of the asymptomatic patient, with basic symptomatic/supportive care. Aggressive IV fluid therapy with lasix is highly encouraged. Prognosis is guarded, depending on the severity of the renal damage.
Category C contains mushrooms of the genera Amanita and Tricholoma, which contain ibotenic acid and muscimol. There is generally a very rapid onset [within few minutes to 2 hours] of abdominal pain, vomiting, ataxia and muscle spasms, which are then followed by neurological signs such as confusion, drowsiness, delirium, hallucinations, agitation, muscle twitching, and seizures [peak effect is usually within 2 to 3 hours]. The usual duration is generally less than 10-24 hours. Treatment consists largely of decontamination of the asymptomatic patient, and symptomatic and supportive care [e.g., diazepam, IV fluids]. Data in the human literature indicate a lethality percentage of up to 12%.
Category D consists of mushrooms in the genera Psilocybe, Panaeolus, Gymnopilus, Conocybe and Stropharia. These are your "magic mushrooms" that contain the hallucinogens psilocybin and psilocin. An estimated toxic exposure is between 1-20 'caps'. Within 30 to 60 minutes of ingestion, one can see vomiting, disorientation, hallucinations, tremors, lethargy and dilated pupils. Most animals recover uneventfully within 6 hours. Dilated pupils, hypertension and drowsiness may last up to 24 hours. Treatment is largely symptomatic and supportive.
Category E consists of those mushrooms [Gyromitra, Helvella, Verpa] that contain the toxin, monomethylhydrazine. Many systems are affected, including gastrointestinal, hepatic, renal, nervous and cardiovascular. Signs of illness may be acute or delayed [6-24 hours up to 2 days], and include vomiting, diarrhea, depression, jaundice, methemoglobinemia, hemolysis, coma and seizures. Treatment options include decontamination in the asymptomatic patient, and fluids, electrolytes, blood transfusion, methylene blue/ascorbic acid, folic acid, and benzodiazepines and pyridoxine in affected patients. The prognosis is guarded.
Category F includes muscarine-containing mushrooms [Coprinus, Clitocybe, Boletus, Inocybe, Entoloma, Mycena, Omphalotus, Amanita). Signs generally appear within 2 hours, and include vomiting, diarrhea, excessive salivation, lacrimation, excessive urination, blurred vision, hypotension and bradycardia, miosis, nasal discharge, and dyspnea [SLUD; SLUDGE, DUMBBELS]. Treatment of affected pets may include atropine, IV fluids, oxygen and bronchodilator.
Category G contains a number of genera, including Agaricus, Amanita, Boletus, Cantharellus, Chlorophylum, Laccaria, Lepiota, Lycoperdon, Omphalotus, Ramaria and Scleroderma, which contain compounds that primarily cause gastrointestinal upset within 30 minutes to 3 hours post ingestion. The clinical signs are usually self-limiting and the patient generally recovers within 1-2 days. There are few serious side effects seen with these mushrooms. Hemolysis has been reported in rare instances.
"Mushroom Poisoning", Compendium on Continuing Education for the Practicing Veterinarian, Vol. 9, No. 8, August 1987, pp. 791-793.
Handbook of Mushroom Poisoning (Ed. D.G. Spoerke, B.H. Rumack), Published by CRC Press, 1994.
The Audubon Society Field Guide to North American Mushrooms (Ed. G.H. Lincoff), Published by Alfred A. Knopf, New York, 1992.
"Mushroom Exposure", In: Small Animal Toxicology (Ed. M. Peterson, PA Talcott), Published by W.B. Saunders, 2006, pp. 860-887.