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Allium spp Toxicosis in Animals


Sharon M. Gwaltney-Brant

, DVM, PhD, DABVT, DABT, University of Illinois

Reviewed/Revised Jun 2021 | Modified Nov 2022

Allium spp toxicosis is characterized by development of hemolytic anemia Hemolytic Anemia in Animals Hemolytic anemia results from loss of RBCs. Immune-mediated destruction is the most common cause in dogs, although infections, tumors, and other causes also occur. Immune-mediated hemolytic... read more Hemolytic Anemia in Animals after ingestion of large amounts of plant material. Toxicosis has been reported in livestock after feeding of onions, and dogs and cats have been affected after ingesting cooked, dehydrated, or granulated forms of onions or garlic. Several days after ingestion, clinical signs of acute hemolytic anemia develop, including weakness, pallor, icterus, and collapse. Treatment entails early decontamination and management of acute hemolytic anemia.

Etiology of Allium spp Toxicosis in Animals

Allium spp include garlic, onions, chives, and leeks, although garlic and onions are the most commonly associated with toxicosis. Garlic is 3–5 times more toxic than onion. Cats are the most sensitive species, followed by dogs; toxicosis in these species is most commonly associated with ingestion of concentrated forms of Allium, such as dehydrated flakes, powders, or dry onion soup mixes. However, toxicosis has been reported in cats after ingestion of less than a teaspoon of cooked onions. Toxicosis also has been reported in livestock, with goats and sheep seemingly more resistant than cattle or pigs; ruminants can develop a tolerance for Allium spp with a gradual increase of their concentration in feed.

Pathogenesis of Allium spp Toxicosis in Animals

Sulfur-containing oxidants in Allium spp are thought to be responsible for the hemolysis that occurs after ingestion. These compounds are released via mechanical disruption of the plant (chopping, cooking, chewing) and by the action of GI microbes on the material. Absorption of these oxidant compounds results in oxidative damage to RBCs, leading to Heinz body formation and methemoglobinemia, which begins within 24 hours and peaks in approximately 72 hours; hemolysis typically occurs 3–5 days after exposure. Hemoglobinuria may result in secondary nephrosis after hemolysis.

Clinical Findings of Allium spp Toxicosis in Animals

Clinical signs of Allium spp toxicosis are generally not noted until substantial hemolysis has occurred, usually a few days after exposure. Depression, anorexia, tachypnea, tachycardia, weakness, exercise intolerance, icterus, hemoglobinuria, collapse, and death may occur.

Diagnosis of Allium spp Toxicosis in Animals

  • Clinical evaluation and patient history of exposure

  • Presence of Heinz body hemolytic anemia +/– methemoglobinemia

Diagnosis of Allium spp toxicosis relies on patient history of exposure, clinical signs, and clinicopathologic confirmation of Heinz body hemolytic anemia; methemoglobinemia may or may not be present by the time extensive hemolysis has occurred.

Treatment of Allium spp Toxicosis in Animals

  • Early GI decontamination

  • Supplemental oxygen or blood transfusion, if needed

  • IV fluids

Life-threatening clinical signs of Allium spp toxicosis should be managed first, including provision of supplemental oxygen and/or blood transfusion as needed. Intravenous fluid therapy is recommended to help protect the kidneys against hemoglobinuric nephrosis.

Gastrointestinal decontamination in cases of recent ingestion is recommended. Emesis should be induced via administration of apomorphine (dogs; 0.03–0.04 mg/kg, IM, IV, SC, or intraconjunctivally, although IV is now preferred due to its speed), 3% hydrogen peroxide (dogs; 2.2 mL/kg, maximum of 45 mL), or dexmedetomidine (cats; 7–40 mcg/kg, IM or 3.5 mcg/kg IV). Administration of activated charcoal is generally recommended in cases of Allium exposure in dogs and cats, but whether it absorbs or prevents production of sulfides derived from Allium is unknown.

Key Points

  • Ingestion of raw or concentrated forms of onions and garlic can result in Heinz body hemolytic anemia in cats, dogs, and food-producing animals.

  • Although Heinz bodies and methemoglobin levels increase within 24 hours of ingestion of Allium spp, clinical signs of anemia may take as long as several days to appear.

  • Treatment involves early decontamination, management of acute hemolytic anemia, and intravenous fluid therapy.

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