Avocado toxicosis occurs after ingesting fruit, stems, leaves, or seeds of the avocado plant. Clinical effects include sterile mastitis in lactating mammals and myocardial necrosis in susceptible mammals and birds. No tests are currently available to aid diagnosis of avocado toxicosis, and treatment is limited to addressing clinical signs.
Ingestion of avocado (Persea americana) has been associated with development of myocardial necrosis in mammals and birds and with sterile mastitis in lactating mammals. Cattle, goats, horses, mice, rabbits, guinea pigs, rats, sheep, budgerigars, canaries, cockatiels, ostriches, chickens, turkeys, lemurs, aye-ayes, and fish are susceptible to these conditions after avocado ingestion. Caged birds seem more susceptible to the effects of avocado, whereas chickens and turkeys seem more resistant.
Although a single case report exists of 2 dogs developing myocardial damage after avocado ingestion, dogs seem relatively resistant compared with other species. In addition, dogs ingesting the intact pit of the avocado fruit can develop foreign body obstruction of the GI tract.
Etiology of Avocado (Persea spp) Toxicosis in Animals
Ingestion of avocado fruit, leaves, stems, and seeds has been associated with toxicosis in animals; leaves are the most toxic part. The Guatemalan varieties of avocado have been most commonly associated with toxicosis.
When purified, persin, the toxic principle in avocado, causes mastitis in lactating mice at 60–100 mg/kg, and doses > 100 mg/kg result in myocardial necrosis. Goats develop severe mastitis after ingesting 20 g of leaves/kg, and ingestion of 30 g of leaves/kg typically results in cardiac injury. Acute cardiac failure occurred in sheep fed avocado leaves at 25 g/kg for 5 days; sheep that were fed 5.5 g/kg of leaves for 21 days or 2.5 g/kg for 32 days developed chronic cardiac insufficiency. Budgerigars fed 1 g of avocado fruit developed agitation and feather pulling, and ingestion of 8.7 g of mashed avocado fruit resulted in death within 48 hours (1). Myocardial injury, mastitis, and colic have been reported in horses that have ingested avocado fruit or leaves.
Pathogenesis of Avocado (Persea spp) Toxicosis in Animals
Avocado ingestion causes necrosis and hemorrhage of mammary gland epithelium in lactating mammals and myocardial necrosis in birds and mammals. Ingestion of persin, isolated from avocado leaves, has caused lesions similar to those reported in cases of avocado ingestion.
Clinical Findings of Avocado (Persea spp) Toxicosis in Animals
In lactating animals, sterile mastitis, accompanied by a 75% decrease in milk production, occurs within 24 hours after avocado ingestion. Affected mammary glands are firm and swollen and produce watery, curdled milk. Lactation may provide some protection against myocardial injury when small amounts of avocado are ingested.
Nonlactating mammals or animals who have ingested a large amount of avocado may develop myocardial insufficiency within 24–48 hours and may exhibit lethargy, respiratory distress, subcutaneous edema, cyanosis, cough, exercise intolerance, and death.
Horses may develop edema of the head, tongue, and breast region.
Birds exhibit lethargy, dyspnea, anorexia, subcutaneous edema of the neck and pectoral regions, and death.
Lesions
Animals with avocado toxicosis have edematous, hyperemic mammary glands and watery, curdled milk. Animals that develop cardiac insufficiency typically have pulmonary and hepatic congestion with dependent subcutaneous edema. Pulmonary edema and free fluid may develop within the abdomen, pericardial sac, and thorax. The heart may have pale streaks.
Histopathological lesions in the mammary gland include degeneration and necrosis of secretory epithelium, with interstitial edema and hemorrhage. Myocardial lesions include myocardial fiber degeneration and necrosis, most pronounced in ventricular walls and septum; interstitial hemorrhage with or without edema may be present.
In horses, symmetric ischemic myopathy of the head muscles and tongue, as well as ischemic myelomalacia of the lumbar spinal cord, has been reported.
Diagnosis of Avocado (Persea spp) Toxicosis in Animals
Clinical evaluation
History of exposure
Diagnosis of avocado toxicosis relies on history of exposure and clinical signs. No specific tests to confirm diagnosis are available. Differential diagnoses include other causes of mastitis (eg, infectious) and other myocardial disorders, including ionophore toxicosis, yew toxicosis, vitamin E/selenium deficiency, gossypol toxicosis, cardiac glycoside toxicosis (eg, oleander), cardiomyopathy, and infectious myocarditis.
Treatment of Avocado (Persea spp) Toxicosis in Animals
Supportive care
Analgesics (eg, NSAIDs) may benefit patients with mastitis caused by avocado toxicosis. Treatment for congestive heart failure (eg, diuretics, antiarrhythmic drugs) may be beneficial but may not be economically feasible in production animals.
Key Points
Birds and livestock exposed to avocado plants or fruits are at greatest risk of avocado toxicosis.
Myocardial injury can be extensive, especially in birds.
Treatment is supportive and focused on managing clinical signs.
For More Information
Also see pet owner content regarding avocado poisoning.
Reference
Burrows GE, Tyrl RJ. Toxic Plants of North America. 2nd ed. Wiley-Blackwell; 2013:744-747.
