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.
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.
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.
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.
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.