Christmas Plants: Hazards, History, and Holiday Dangers

The Christmas season is filled with wonderful scents, lights, and music. Homes are filled with family and friends. Plants and bouquets are frequently presented as gifts, and homes are decorated with more flowers and plants than at many other times of the year. Dogs and cats, being curious, are likely to investigate new plants. Cats tend to nibble on them, while dogs are more likely to ingest the entire plant, including the soil, roots, or bulb. In all cases of plant ingestion, it is important to identify the ingested plant, ideally with the genus and species name.

Welcome to Practical Toxicology, brought to you in partnership between Today’s Veterinary Practice and the ASPCA Animal Poison Control Center (APCC). This column provides practical clinical information about diagnosing and treating pets that have been exposed to potentially harmful substances.

The APCC:

• Provides 24-hour diagnostic and treatment recommendations by specially trained veterinary toxicologists
• Protects and improves animal lives through toxicology education, consulting services, and case data review
• Developed and maintains AnTox, an animal toxicology database system that identifies and characterizes toxic effects of substances in animals
• Works closely with human poison control centers to provide animal poisoning information
• Offers extensive veterinary toxicology consulting to organizations in industry, government, and agriculture.

If treating a patient that requires emergency care for poisoning, call the APCC at 888-426-4435.

When obtaining a medical history for a pet with clinical signs of toxicosis, also obtain a list of plants in the home or yard. If clinical signs fit a potential exposure to a known plant in the environment, the plant can be included in the rule-out list and appropriate therapy initiated. If clinical signs are not consistent with plant ingestion, the owner should be asked about other substances, such as insecticides and fertilizers, that might have been added to soil. Owners are not always aware whether a pet has ingested a leaf, eaten the dirt around the plant, or drunk from a pot reservoir. Water in the reservoir of pots may contain the toxic principle of poisonous plants (like cardiac glycosides) or added substances (like insecticides).

Amaryllis (Amaryllis or Hippeastrum species)

Amaryllis is native to South America. It can be forced to bloom in winter, generally during the holiday season. The flowers come in a variety of colors, with red being popular for Christmas.

Like other members of the Amaryllidaceae family, amaryllis contains the phenanthradine alkaloids lycorine and tazetine. These alkaloids reach concentrations of up to 0.5% in the bulb and leaves. Lycorine is the toxic principle responsible for most of the clinical effects. Lycorine acts on neurokinin-1 receptors, with some effect on the 5-hydroxytryptamine receptors. Many other alkaloids are present in the plant as well.

A lycorine study in dogs demonstrated that 0.5 to 2 mg/kg SC causes nausea and vomiting.² At 2 mg/kg SC, 100% of dogs vomited. The gastrointestinal effects of lycorine in the study lasted 2.5 hours. However, the oral bioavailability of lycorine in dogs is only 40%. Clinical signs would likely last longer when plant material is ingested and remains in the gastrointestinal tract.

For most pets, ingesting leaf material results only in mild gastrointestinal upset, with clinical signs that may include mild to moderate vomiting, diarrhea, anorexia, and hypersalivation. Ingestion of portions of the bulb may cause more intense clinical signs, such as restlessness, tremors, or dyspnea, while large or massive bulb ingestions could cause hypotension, seizures, and sedation.

Most cases of vomiting are managed at home by withholding food and water for several hours; additional treatment is rarely required. Moderate to severe vomiting can be managed with antiemetics. Maropitant (Cerenia; zoetisus.com) is a neurokinin-1 receptor antagonist and is the antiemetic of choice. In a study of lycorine-induced vomiting in beagles, maropitant completely blocked vomiting when given before lycorine was administered.^1,2 On the basis of ASPCA Animal Poison Control Center data, maropitant is an effective antiemetic for pets that begin vomiting after amaryllis ingestion. Other antiemetics (ondansetron, metoclopramide) are not as effective as maropitant in these cases.

Other supportive care includes IV fluids and, in severe cases, correction of electrolyte imbalances. Large ingestions of leaves and bulbs may require decontamination with induction of emesis (if within an appropriate time frame). Massive ingestions may require blood pressure monitoring. Prognosis is generally good for amaryllis ingestions, and, in most cases, signs resolve within 24 hours.

Christmas Cactus (Schlumbergera truncata)

Christmas cactus is a native Brazilian plant and a member of the cactus family (another common name is crab’s claw cactus). The plant is light sensitive and can be forced to bloom seasonally.

In dogs and cats, the most common clinical signs of toxicosis include vomiting, lethargy, anorexia, diarrhea, and hypersalivation. Bloody vomiting and diarrhea can also occur. Ataxia has been reported in cats. Clinical signs are generally mild and resolve within a few hours.

Treatment is generally managed at home by withholding food and water and giving the gastrointestinal tract a chance to recover. If vomiting or diarrhea is moderate to severe, the animal may require antiemetics and correction of dehydration or electrolyte imbalances. A bland diet may be indicated for several days.

Christmas Trees

Christmas trees are the ultimate Christmas season plants. Common species include firs (Abies and Pseudotsuga species), pines (Pinus species), cypresses (Cupressus species), spruces (Picea species), and cedars (Juniperus and Cedrus species). Most Christmas trees are cut before being brought into the house, although some have a root ball so the tree can be planted outdoors after the holidays. Cut trees are usually placed in a stand with a reservoir for water. Frequently, preservatives containing dextrose and fertilizers are added to the water. Drinking the preservative–water mix typically causes only mild, self-limiting gastrointestinal upset. If the water is not routinely changed, bacterial or fungal overgrowth can occur.

Pets may ingest needles, cones, branches, and bark. Most Christmas trees contain essential oils (concentration and specific oils vary by species). Ingestion of large quantities of needles, cones, and parts of the tree may result in a gastrointestinal foreign body.

Although long-term ingestion by livestock causes reproductive losses and concentrated essential oils and extracts can cause central nervous system signs, such as seizures, the amount of essential oil a pet is likely to ingest is minimal. The most common clinical signs of ingestion include vomiting, anorexia, abdominal pain, and depression. Some trees have sharp needles, which can cause mechanical irritation and trauma to the mucosa of the alimentary tract. Signs are generally mild and self-limiting. Typical signs of a foreign body (abdominal distension, persistent vomiting) may occur.

Most cases are managed at home by withholding food and water for several hours. For severe or protracted vomiting, antiemetics may be indicated. Gastrointestinal protectants (sucralfate slurries for mucosal irritation) may be helpful for large ingestions or protracted vomiting. If dehydration is present, replace fluids and correct any electrolyte abnormalities. If a foreign-body obstruction develops, surgical or endoscopic removal of the plant material may be required. In most cases, prognosis is good.

Holly (Ilex aquifolium)

Holly has shiny green leaves with sharp spines and bright red drupes (generally referred to as berries). It is used in wreaths and other decorative trimming. Holly is also planted in gardens.

The sharp leaves can cause mechanical damage. Several potentially toxic substances are found in holly, including methylxanthines and cyanogens, as well as saponins. Significant intoxication usually involves ingestion of concentrated extracts. In plant ingestions, the primary toxic effect in dogs and cats is gastrointestinal irritation from the saponins. Some animals may ingest enough leaf material to cause a foreign-body obstruction, but this is rare.

Typical clinical signs include hypersalivation, vomiting, diarrhea, head shaking, lip smacking, and potential mechanical injury resulting in mild oral ulceration or laceration.

Most holly ingestions can be managed at home. If large quantities of plant material were ingested, bulk up the diet (eg, with bread). Emesis may be attempted for significant ingestions. Mild vomiting can be treated by withholding food and water. Prolonged or significant vomiting can be treated with antiemetics. If oral discomfort is present (head shaking, lip smacking), rinse the mouth with water and administer sucralfate slurries. Evaluate and treat as needed for a foreign-body obstruction if vomiting is protracted. Prognosis is good. Most cases resolve in a few hours.

Kalanchoe (Kalanchoe blossfeldiana)

Kalanchoe has only recently been associated with Christmas. These plants can be forced to bloom during winter, and red kalanchoes are popular Christmas gifts. Because this is a year-round houseplant, ingestions can occur at any time. Dwarf varieties are used as houseplants.

Kalanchoe is a cardiotoxic plant; other cardiotoxic agents are listed in Box 1. The toxic principle is bufadienolides, which are found in all parts of the plant, but are concentrated in the flowers. Bufadienolides inhibit the Na-K adenosine triphosphatase in the myocardial cell membrane. This causes an increase in intracellular sodium and a decrease in intracellular potassium. The net result is a reduction in the normal membrane resting potential, which reduces the myocardium’s ability to act as pacemaker. The loss of the normal myocardial electrical function can result in asystole. Hyperkalemia is seen in severe toxicosis. Dogs are reported to be especially sensitive to the cardiotoxic effects of bufadienolides. However, most of the potted dwarf varieties of kalanchoe cause only mild gastrointestinal effects; cardiovascular signs are uncommon.

The most common clinical signs in dogs and cats are vomiting, depression, lethargy, and diarrhea. Other reported signs include weakness, dyspnea, anorexia, tachycardia, and vocalization. Neurologic signs have been reported in dogs and include nystagmus, tremors, seizures, and disorientation.

Ingestion of kalanchoe warrants decontamination (asymptomatic pets only). Monitor pets for clinical signs at a veterinary hospital. In most cases, signs develop within a few hours, but onset can be delayed up to 12 hours. Any pet developing clinical signs after kalanchoe ingestion should have heart rhythm, blood pressure, and electrolytes monitored. Hyperglycemia has been reported in kalanchoe intoxications, although many cardiotoxic substances cause hypoglycemia instead. Gastrointestinal signs are managed as needed, and fluids should be administered. Add dextrose to the fluids if hyperkalemia is present. Manage vomiting and gastrointestinal clinical signs with antiemetics and histamine-2 blockers.

Antiarrhythmic drugs (Table 1) should be used as needed. Treat the specific arrhythmia. A digoxin-specific immune Fab (Digibind; DigiFab, digifab.us) is indicated when serum K+ >5 mEq/L or if arrhythmias do not respond to standard therapy. In most veterinary cases, the initial dose is 1 to 2 vials empirically. The vials should be reconstituted in sterile water and then added to 50 mL of saline. Administer IV over 30 minutes (improvement is noted within 20 minutes to a few hours).

Monitor potassium and electrocardiograms while maintaining fluid therapy. Sometimes, the toxin redistributes in tissues and signs reappear. The prognosis is excellent if only mild gastrointestinal signs develop. If significant cardiovascular signs and/ or hyperkalemia develop, the prognosis is guarded.

TABLE 1. Antiarrhythmic Therapies for Dogs and Cats

[ultimatetables 16 /]

Mistletoe (Phoradendron species)

There has been significant confusion over the years between European and American mistletoe; the genus discussed here, Phoradendron, is the American mistletoe. The plants are semiparasitic and live on tree branches. One theory suggests toxicity may vary depending on the species of tree in which the mistletoe grows.

Mistletoe contains a variety of potentially toxic compounds, although serious signs are uncommon. Human poison control centers have published retrospective studies of mistletoe ingestions. Most people remained asymptomatic, and gastrointestinal effects were the primary clinical signs in symptomatic cases. In rare cases, hypotension, collapse, ataxia, seizures, and death were reported.4–6

Mistletoe contains glycoprotein lectins, which are same type of toxin found in castor beans (Ricinus communis). Mistletoe lectins (phoratoxin and ligatoxin A) are significantly less toxic than ricin. The toxins act as a cardiac depressant, causing hypotension, bradycardia, and decreased contractility.

The most common clinical signs include vomiting, depression, and diarrhea. Rarely, with large ingestions, hypotension may be seen. Most ingestions are managed at home by withholding food and water. Large ingestions warrant decontamination. Pets experiencing more than mild gastrointestinal upset should be evaluated for hypotension. Prognosis is generally good.

Poinsettia (Euphorbia pulcherrima)

Poinsettia is an especially popular Christmas plant. The upper leaves come in a variety of colors and resemble a flower. The flowers are the tiny yellow structures resembling stamens. Poinsettias have received a great deal of negative publicity based on a probable urban legend from 1919.

All Euphorbia plants produce a milky sap containing latex irritants. However, poinsettias are much less potent than many Euphorbia species. Diterpenoid euphorbol esters and steroids with saponin-like properties in the sap are the toxic principle and have a “soapy” effect on tissues. Dermal exposures in pets can cause pruritus, erythema, and irritation. Ocular exposure may lead to conjunctivitis. Ingestion irritates the mucosa, resulting in hypersalivation, vomiting, and possibly diarrhea. Clinical signs are expected to be mild and self-limiting, and frequently no medical treatment is required.

Large ingestions can be diluted with milk and water. Owners should withhold food and water for several hours if vomiting occurs. The pet should be bathed with a mild shampoo and water if sap is on the coat. In cases of ocular exposure, flush eyes with saline or tepid tap water. Prognosis for full recovery is excellent.

Rosemary (Rosmarinus officinalis)

Rosemary is known as the herb of love and remembrance. A small evergreen shrub, it has a rich, pungent flavor and a pleasant aroma. Although exposure to rosemary occurs year round, rosemary is often trimmed into a pine tree shape for a miniature Christmas tree.

Rosemary contains a variety of volatile essential oils. In small quantities (such as the amount used in cooking), no toxic effects are seen. However, large ingestions of extracts or oils can result in gastrointestinal upset and irritation, as well as renal and neurologic effects. The mechanism of toxicity is not well understood. Gastrointestinal signs are most likely due to a direct irritant effect. The hypotensive effects are due to the spasmolytic action on smooth and cardiac muscles. Finally, the convulsant effect is theorized to be caused by monoterpene ketones. Reproductive effects are possible but rarely a concern in dogs and cats.

Small to moderate ingestions may cause nausea and vomiting, as well as diarrhea. Large ingestions, in addition to gastrointestinal signs, may cause hypotension, weakness, pale mucous membranes, depression, acute kidney injury, and seizures (humans). Seizures are most likely due to monoterpene ketones.7

Most cases causing significant clinical signs involve concentrated oils and extracts. Ingestion of the plant typically causes only mild gastrointestinal upset, which can be managed by a pet owner at home by withholding food and water for 1 to 2 hours. If vomiting and diarrhea worsen, the animal should be transported to the veterinarian. In cases of large ingestion, induce emesis. Antiemetics, fluid therapy, and pressor agents (drugs that raise the arterial blood pressure, such as epinephrine or norepinephrine) should be used in cases of hypotension. Obtain a complete blood count and chemistry profile and manage seizures if needed.

Antiemetics, fluid therapy, and pressor agents (drugs that raise the arterial blood pressure, such as epinephrine or norepinephrine) should be used in cases of hypotension. Obtain a complete blood count and chemistry profile and manage seizures if needed.

Star-Of-Bethlehem (Ornithogalum species)

Star-of-Bethlehem is a perennial plant that grows from a bulb. Most plants are grown outdoors, although some dwarf varieties are potted. Because of the star-shaped petals, this plant is frequently included in bouquets around the Christmas holidays. All parts of the plant are toxic, although the toxins are concentrated in the bulb.

This plant contains 2 alkaloids: convallatoxin and convalloside. These are cardiac glycosides. Clinical signs and treatment are similar to those for kalanchoe ingestion. Pets generally have access only to the foliage, and most ingestions of cut flowers result in mild clinical signs.

Summary

Although pets are more likely to be exposed to these plants at Christmas, ingestions are unlikely to cause serious, life-threatening signs. Most cases can be managed at home. Advise clients to gift pet-safe bouquets and houseplants to friends and family members who have pets. Some common safe houseplants include African violets and orchids. Suggestions for cut flowers include roses, Alstroemeria species (Peruvian or Brazilian lily), Gerbera daisies (Gerbera jamesonii), snapdragons, and sunflowers.