Mistletoe Poisoning

As much as we may like to kiss under mistletoe, we humans don’t usually eat it. But our pets may have other ideas.

Mistletoe is a semiparasitic vine that takes water and inorganic nutrients from its deciduous tree host while carrying out some photosynthesis on their own. There are 43 species of mistletoe, eight of which are of toxic significance. Phoradendoron flavescens, the American mistletoe, primarily parasitizes oak or walnut trees while Viscum album, the European mistletoe, prefers apple trees. These two species of mistletoe are the most commonly implemented in toxicities. Both American and European mistletoe have ovoid leaves which are opposite in arrangement along the stem. The flowers are tiny and inconspicuous with the fruits being white.

Pets become exposed when the vine is bought into the home for use as holiday decoration. It is an English custom that any two people who meet under a hanging piece of mistletoe are obliged to kiss each other. According to tradition, the mistletoe must not touch the ground between its cutting and its removal as the last of the Christmas greens after Christmas Eve.

Alternatively, the American Indians used mistletoe as an abortifacient.

Many toxins have been found in various species of both American and European mistletoe. These toxins include glycoprotein lectins, phoratoxins, aminobutyric acid, alkaloids, phenethylamines, and flavonoids.

Clinical signs occur within 2 to 24 hours after ingestion of the leaves, berries, or a tea made from the berries. Clinical signs of poisoning are typically a severe gastroenteritis with prolonged emesis (vomiting), followed by depression. In spite of the number of toxic substances available, serious poisonings are infrequent. The more severe clinical signs have been reported in human literature through the consumption of a home-brewed mistletoe abortifacient tea. In 1968, a twenty year-old woman used this tea to abort and within two hours of its consumption became violently ill. She reportedly had abdominal pain, vomiting, diarrhea, and cardiovascular collapse followed by hypotension (low blood pressure), resulting in death within 12 hours of the tea’s consumption.

Treatment associated with any of these plants is symptomatic and supportive. Treatment is aimed at decreasing gastrointestinal distress and assuring that the pet does not become dehydrated or develop an electrolyte imbalance. Demulcents and antacids are often of great benefit.

References:

Ettinger, Stephen. and Edward Feldman. Veterinary Internal Medicine. 6th Ed. Vol. 1. 2005. Elsevier. p.252.

Kahn, Cynthia ed. The Merck Veterinary Manual. 9th Ed. 2005. Pp. 2438-2439.

Volmer, Petra DVM. “How Dangerous are Winter and Spring Holiday Plants to Pets?” Veterinary Medicine. December 2002. p. 879.

“Mistletoe” from Wikipedia, the free encyclopedia.

Fowler, Murray. Plant Poisoning in Small Companion Animals. Ralston Purina. 1981. Pp. 12-14.