Dogs with heritable high erythrocyte reduced glutathione and potassium concentrations are more susceptible to the hematologic effects of onions.¹² This trait is relatively common in Japanese breeds. Other inborn errors in metabolism or nutritional deficiencies that result in decreased erythrocyte antioxidant defenses, such as glucose-6-phosphate dehydrogenase deficiency or zinc deficiency, could increase an animal's susceptibility to Allium species toxicity.¹³ Concurrent treatment with xenobiotics, drugs, or dietary factors that induce erythrocyte oxidative injury (e.g. propofol, propylene glycol, dl-methionine, sulfonamides, sulfapyridine, large doses of vitamin K₃, benzocaine) or diminish erythrocyte oxidative defenses (e.g. acetaminophen) is likely to increase an animal's susceptibility to Allium species toxicosis.

Clinical signs and laboratory findings

In dogs and cats, clinical signs of Allium species toxicosis may appear within one day of consumption if large amounts of material have been ingested; however, it is more common for clinical signs to develop after a lag of several days. Clinical signs often include depression, hemoglobinuria, hemoglobin and possibly hemosiderin urinary casts, icterus, tachypnea, tachycardia, weakness, exercise intolerance, and cold sensitivity. Inappetence, abdominal pain, and diarrhea may also be present. In cases of recent ingestion, the affected dog's or cat's breath may smell of onions or garlic.

Necropsy and histologic findings typically indicate hemolytic anemia. Because of the common lag of several days between ingestion and the development of clinical signs, gastrointestinal erosion or Allium species in the gut content may not be seen. Histopathologic findings, although consistent with hemolytic anemia, are not specific for Allium species toxicosis and may include deposition of hemosiderin in the phagocytic cells of the liver, spleen, and renal tubular epithelium; renal tubular pigment necrosis; and nephrotubular casts and hemoglobin casts in the renal tubules.¹

Differential diagnoses

Differential diagnoses include other common toxicoses: brassicaceous vegetables, propylene glycol, acetaminophen, benzocaine, vitamin K₃, dl-methionine, naphthalene, zinc, and copper. Common feline disorders associated with Heinz body formation include diabetes mellitus, particularly if ketoacidosis is present; hepatic lipidosis; hyperthyroidism; and lymphoma and other neoplasms.

Diagnosis and treatment

Allium species toxicosis is typically diagnosed through a combination of history, clinical signs, and microscopic confirmation of a Heinz body-type hemolytic anemia.

No specific antidote is available for Allium species toxicosis. Treatment involves gastrointestinal decontamination and removing the Allium species source, treating the anemia, and providing general supportive care. Inducing emesis can be valuable in asymptomatic dogs and cats provided no complicating factors are present and ingestion was within the last one or two hours. Consider administering activated charcoal after emesis. In severely affected animals, a blood transfusion and supplemental oxygen therapy may be required. Administering intravenous crystalloids is indicated if extensive vomiting and diarrhea have occurred or if hemoglobinuria or hypotension is evident.

Carefully monitor the patient's erythron for several days after ingestion since that is when the anemic nadir usually occurs. Antioxidants, such as sodium ascorbate, vitamin E, and N-acetylcysteine, have minimal overt protective effects in onion powder toxicosis in cats.¹⁴ Diets low in potential oxidants are recommended; semimoist foods that contain propylene glycol should be avoided, particularly in cats.¹⁵

A patient's prognosis depends on the species of plant involved, the severity of the anemia, and the institution of supportive care. In companion animals, avoiding exposure is the best preventive strategy. Feeding pets onions or other Allium species or their derivatives should be stopped.

"Toxicology Brief" was contributed by R.B. Cope, BSc, BVSc, PhD, Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331. The department editor is Petra Volmer, DVM, MS, DABVT, DABT, College of Veterinary Medicine, University of Illinois, Urbana, IL 61802.

REFERENCES

1. Burrows GE, Tyrl RJ. Liliaceae Juss. Toxic plants of North America. Ames: Iowa State Press, 2001;751-805.

2. Amagase H, Petesch BL, Matsuura H, et al. Intake of garlic and its bioactive components. J Nutr 2001;131:955S-962S.