Chapter 37 Christmastime Plants
Christmastime brings with it a large assortment of plants that are used for decorative purposes throughout the holiday season. Because of their novelty, when they seasonally appear in the house, and because these plants are kept primarily indoors, there is increased potential for household pets to be exposed to them. Both dogs and cats have been known to chew on houseplants, with the primary difference between these two species being the amount of plant material ingested. Although cats often only nibble on a few leaves, many dogs will devour the entire plant, including potting soil, if the opportunity arises. Other indoor pets, such as birds and rabbits, may similarly be exposed to these decorative plants. Fortunately, few of the plants common to the Christmas holiday have the potential to cause serious or life-threatening signs in pets if ingested, and the majority are generally expected to cause at most mild gastrointestinal upset.
When dealing with an exposure of a pet to any plant, it is important to determine the identity of the plant (ideally genus and species name) and whether any plant care products (especially systemic insecticides) may have been applied to the plant or soil.
AMARYLLIS (HIPPEASTRUM SPP.)
Amaryllis (Hippeastrum spp.) is a popular Christmastime plant, native to South America, which blooms from late December until early June. The large blossoms occur in a variety of solid, striped, or variegated colors ranging from white to salmon to red.
Mechanism of toxicity
Amaryllis and other members of the Amaryllidaceae family contain phenanthridine alkaloids, such as lycorine and tazetine.1 The alkaloids are primarily concentrated within the bulb and leaves where they can be present in concentrations up to 0.5%. Lesser amounts of alkaloids are present in the bulbils and flowers. Lycorine, the principal alkaloid responsible for clinical effects, is a centrally acting emetic, and various other alkaloids have cholinergic, analgesic, hypotensive, and cytotoxic effects. In most pets, chewing on or ingesting leaves generally only causes mild gastrointestinal upset, and ingestion of parts of the bulb may lead to more severe signs.1,2
Mild to moderate vomiting, diarrhea, anorexia, and hypersalivation are the most common signs seen when animals ingest leaves, flowers, or small amounts of amaryllis bulb.2 More severe gastrointestinal upset may be manifested by restlessness, tremors, or dyspnea.1 Less commonly, hypotension, sedation, or seizures may occur, especially if large amounts of bulb material have been ingested.2 In humans asthma has been associated with exposure to amaryllis, but this has not been reported in small animals.3
Because protracted vomiting and/or diarrhea may result in dehydration and electrolyte abnormalities, animals showing severe or prolonged gastrointestinal upset should have their hydration and electrolyte status monitored. Hepatopathy has occasionally been reported to be associated with amaryllis ingestion,2 so measurement of baseline and 72-hour liver enzyme values may also be indicated in more severe cases. Complete evaluation of hematological and serum biochemical values is usually prudent for aged animals or those with preexisting health problems.
Decontamination via emesis and/or administration of activated charcoal should be considered with ingestion of large amounts of leaf material or when parts of the bulb have been ingested. Symptomatic care in animals displaying mild clinical signs might include maintaining the animal with nothing per os for a few hours to allow the stomach to rest. Moderate to severe or persistent vomiting may necessitate the use of antiemetics and/or gastrointestinal protectants. Intravenous fluid therapy and correction of electrolyte abnormalities may be required in severe cases. Seizures, should they occur, can usually be managed by the use of diazepam or barbiturates to effect.
In most cases of amaryllis ingestion, the prognosis is very good, and signs usually resolve within 24 hours. Ingestion of large amounts of bulb material or ingestion of amaryllis by animals with prior health conditions may result in more severe signs or prolongation of the course of the toxicosis.
Gross and histological lesions
No significant gross or histopathological lesions have been reported in association with amaryllis ingestion in small animals.
Differential diagnoses for the gastrointestinal upset caused by amaryllis ingestion could include ingestion of other gastrointestinal irritants (e.g., other plants, arsenic, lead, zinc, zinc phosphide poisoning), bacterial or viral gastroenteritis (e.g., parvoviral enteritis), and pancreatitis.
CHRISTMAS CACTUS (SCHLUMBERGERA TRUNCATA)
Christmas cactus (Schlumbergera truncata), also known as crab’s claw cactus, is a member of the cactus family that is native to the jungles of Brazil.4 These popular cacti have flattened, spineless branches tipped with flowers that range in color from red to pink, white, yellow, or orange.
Mechanism of toxicity
In humans exposure to Christmas cactus has occasionally been associated with type 1 hypersensitivity, resulting in urticaria and rhinoconjunctivitis.5 However, in dogs and cats, the primary clinical effects are due to irritation of the gastrointestinal tract from ingested leaves.4
Clinical signs following ingestion of Christmas cactus include vomiting (with or without blood), diarrhea (with or without blood), depression, and anorexia.4,6 In cats ataxia has occasionally been reported as well.6 These signs are generally mild and rarely require more than withholding of food and water to allow the digestive tract to recover. Aged animals or animals with preexisting health conditions may experience more moderate to severe signs requiring veterinary intervention including the use of antiemetics or antispasmodics, and correcting any hydration or electrolyte abnormalities.
In most cases of Christmas cactus ingestion, there is little need for evaluation of clinical laboratory values because signs are generally mild and transient. Animals showing more than mild signs should have clinical laboratory values evaluated to rule out other potential causes for the clinical signs.
The prognosis for complete recovery following ingestion of Christmas cactus is excellent in most cases, with signs often subsiding within a few hours of ingestion.4
Gross and histological lesions
No specific lesions would be expected with ingestion of Christmas cactus.
Differential diagnoses for the clinical signs produced by ingestion of Christmas cactus include dietary indiscretion and other causes of mild, self-limiting gastrointestinal upset. Signs that are persistent or especially severe should lead the clinician to reevaluate the animal to rule out other potential causes of gastrointestinal upset.
A large variety of evergreen trees are sold for use as Christmas trees in the United States. Generally the broad categories of trees that are most commonly used as Christmas trees include the firs (Abies spp., Pseudotsuga menziesii), pines (Pinus spp.), cypresses (Cupress spp.), spruces (Picea spp.), and cedars (Juniperus spp. and Cedrus spp.). Christmas trees are most commonly cut before being brought indoors, although occasionally live trees with root-balls will be used as Christmas trees, with the trees planted outdoors after the holiday is over. Indoor pets may ingest needles, cones, branches, or bark from the trees. Cut trees are usually placed in a receptacle into which water is placed, and pets may also be exposed to sap and soluble plant components by drinking the water in the receptacle. (A word about commercial Christmas tree preservatives: these products usually are composed of small amounts of fertilizer and dextrose and are in themselves unlikely to produce more than mild gastric upset if ingested from the water receptacle. However, the potential exists for bacterial or fungal growth over time if the water-fertilizer substance is not routinely changed and could result in more severe gastroenteritis if the contaminated water-fertilizer substance is ingested. Older preservatives may contain copper sulfate; this could potentially be hepatotoxic.)
Mechanism of toxicity
The seed cones from some species of Juniperus have been used as food by wildlife and humans, and seed cones and foliage from other Juniperus species have been used medicinally for their diuretic and uterine stimulant effects.1 Needles, branches, and bark of many of the evergreens used as Christmas trees contain monoterpenes and diterpenes and a variety of essential oils. Some of the terpenes and essential oils have been demonstrated to produce fetal deaths and malformations in laboratory rodents.7 In livestock, ingestion of green or dry needles, bark, or budding branches of various evergreen plants has been associated with stillbirths, abortions, and other reproductive disorders.1 Reproductive effects in livestock generally require ingestion of relatively large amounts of plant material over days to weeks. In small animals, where relatively small amounts of evergreen material might be ingested and chronic ingestion is unlikely, reproductive effects would not be expected. Concentrated essential oils of a variety of evergreens (e.g., thujone from cedar oil) have been shown to cause CNS effects, including seizures in animals,8 but exposure to the level of essential oils in Christmas tree material is unlikely to cause significant CNS effects in pets.
The mechanisms of action for the majority of the constituents of Christmas tree evergreens are not known. Some Juniperus species contain podophyllotoxin, which binds tubulin, resulting in arrest of cell division in metaphase and that may contribute to the teratogenic and reproductive disorders seen in livestock ingesting these plants.1 Some volatile oils in evergreens have been demonstrated to induce hepatic P450 enzymes, which can alter xenobiotic metabolism.9 In small animals, ingestion of plant material would be expected to cause gastrointestinal upset, either through mechanical irritation or irritation from terpenes or essential oils. Rarely, ingestion of large quantities of evergreen needles, bark, or cones might result in gastrointestinal foreign body obstruction.
In small animals, the most common clinical signs expected with ingestion of evergreen tree material are vomiting, anorexia, abdominal pain, and depression (American Society for the Prevention of Cruelty to Animals [ASPCA] Animal Poison Control Center, unpublished data). Some varieties of evergreens have sharp needles and/or cones, which may cause mechanical trauma to mucous membranes of the alimentary tract. In most cases clinical signs are expected to be mild and self-limiting, although animals with preexisting health problems may be at increased risk for complications, such as dehydration or electrolyte imbalances. Typical signs of gastrointestinal foreign body obstruction (e.g., abdominal discomfort and persistent vomiting) may occur following ingestion of large quantities of plant material.
Because signs from ingestion of Christmas tree material are expected to be mild, laboratory evaluation is rarely necessary, although monitoring of hydration and electrolyte status is recommended in animals with preexisting health problems. Animals with severe or protracted vomiting should receive a complete laboratory work-up to rule out foreign body obstruction and other potential causes of vomiting (e.g., pancreatitis, liver disease, renal disease).
In most cases clinical signs associated with ingestion of Christmas tree material are self-limiting and require little treatment beyond withholding food and water to rest the gastrointestinal tract. Antiemetics would be indicated for severe or protracted vomiting, and gastrointestinal protectants (e.g., sucralfate slurries) or antibiotics may be beneficial if there is evidence of mechanical mucosal injury. Correction of hydration and/or electrolyte abnormalities via the use of crystalloid fluid therapy might be required in rare instances. Treatment of foreign body obstruction (e.g., surgical or endoscopic removal of plant material) might be required in rare cases where large amounts of plant material have been ingested.
The prognosis for animals ingesting Christmas tree material is very good, and most signs are expected to be mild and self-limiting. Animals having more severe or protracted signs should be worked up for other potential causes of gastrointestinal distress.
Gross and histological lesions
Other than potential mechanical damage to oral, pharyngeal, and gastric mucosa, no significant lesions are expected from ingestion of Christmas trees by pets.