Introduction

• A large plant group of mostly perennial bulbous herbs with characteristic aroma.
• Group includes onion, spring onion, shallots, field garlic, garlic, chives, leeks, wild or wood garlic, crow or false garlic.
• All parts of the plants should be considered toxic.
• The onion (Allium cepa) is the most significant toxicologically in cats.
• Signs: gastrointestinal effects, dehydration and subsequent development of hemolytic anemia and Heinz body formation.
• Diagnosis: signs and case history.
• Treatment: gastric decontamination if appropriate, with symptomatic and supportive care. Emphasis on addressing a potential hemolytic anemia.
• Prognosis: fatal cases are rare.

Pathogenesis

Etiology

• Ingestion of plants or plant extracts.
• Note that cooked plant material may still be hazardous.
   

Predisposing factors

General

• Cats appear particularly susceptible to ingestion of plants from this group.

Specific

• Hemoglobin in cats is particularly susceptible to oxidative denaturation. Splenic removal of Heinz body-containing red blood cells is very efficient in cats, and the presence of Heinz bodies does not always lead to a hemolytic event.
• Heinz body formation has been reported in cats fed baby food containing onion powder.
• A dosage as low as 5 g/kg BW may lead to hematological abnormalities.

Pathophysiology

• The toxic mechanism has not been fully elucidated and probably multifactorial.
• Toxins are thought to be a group of structurally similar disufides and thiosulfate compounds.
• N-propyl disulfide depletes glucose-6-phosphate dehydrogenase (G6PD) within erythrocytes diminishing the protective effect of glutathione, as this remains in its oxidized state.
• In this state glutathione forms mixed sulfide bonds with hemoglobin and precipitates within the cell resulting in the formation of Heinz bodies.
• These affected cells are usually removed from circulation by the reticuloendothelial system, thereby inducing anemia.
• There is evidence to suggest that there are other oxidative extracts within the plant material that may directly induce methaemoglobinemia and Heinz body formation.

Timecourse

• Onset of signs is variable, although signs are usually apparent within 6-24 hours.
• Signs of hemolytic anemia or methemoglobinemia may be delayed for 1-5 days.
• Full recovery may take 7 days or more.

Diagnosis

Treatment

Outcomes