Japanese Yew Poisoning in Dogs

Unfortunately, the consumption of yew by pets is often fatal, with clinical signs or death occurring minutes or days after. If you suspect your dog has ingested a portion of the Japanese yew, it is vital that he is seen by a veterinarian immediately.

The Japanese yew is a commonly known cause of fatal poisoning in pets. These plants are common shelter, shade, and ornamental plants in the United States and Canada. The toxic chemicals in the plant, taxine alkaloids can have a severe effect on the heart. Oil irritants in the plant can also trigger gastroenteritis, causing vomiting and diarrhea. 

Clinical signs can take effect within minutes of exposure. Unfortunately, in some cases, the first symptom of yew toxicosis is unexpected death. If clinical signs are noticed they may include:

• Nausea, vomiting, and diarrhea
• Ataxia
• Dyspnea 
• Weakness and trembling
• Central nervous system disturbances may be observed, involving mydriasis, tetanic seizures and aggression
• Gastroenteritis is often also a symptom

Types 

Yew is a common name given to numerous plant species in the United States. They are often chosen as an ornamental plant, used for shelter, shade or as hedges. Their leaves are distinctive, and needlelike.  The Japanese yew is the most popular of the species planted in North American gardens.

Other common species of yew are:

• Taxus cuspidata (Japanese yew), T. baccata, and Taxus x media
• Taxus canadensis (Canada yew, ground hemlock, American yew)
• Taxus brevifolia (Pacific or western yew)

Yew poisoning is caused by various chemicals present in the plant. The lethal dose of ingested leaves for dogs is 2.3g/kg, or 11.5mg/kg of taxine alkaloids. Due to the toxicity of the plant it is possible for a pet to suffer poisoning from playing with branches from the trees.

Taxine alkaloids remain in the plant year round with increased concentrations over winter months. Both taxines A and B are considered cardio-toxic, however taxine B is known to be more potent. These chemicals are direct cardiac myocyte calcium and sodium channel antagonists which affect the heart by inhibiting calcium and sodium currents. This creates potential for increased coronary arterial vasodilation and blood flow and suppressed cardiac contractility, sinoatrial node automaticity, and AV node conduction. In animals who ingest a lethal dose, death is contributed to diastolic cardiac standstill and, in some cases, concurrent arterial vasodilation and hypotension.

Another component of this plant, paclitaxel has been shown to be arrhythmogenic in humans, however, is not considered to be the major chemical responsible for the cardio-toxic effects. Volatile oils may also be ingested from the plant causing the gastrointestinal symptoms of vomiting and diarrhea. The process that causes the central nervous system disturbances most commonly seen in non-lethal poisonings is not currently known.

The veterinarian will make a diagnosis of Japanese yew poisoning by assessing your pet’s clinical history, symptoms and possible access to the plant. In cases where emesis has taken place, the stomach contents will be inspected for residual plant matter. It is possible to diagnose by testing with blood by gas or liquid chromatography and mass spectroscopy, though this is not considered feasible due to the acute nature of the illness.

There is no known antidote for yew poisoning and treatment involves trying to reduce the symptoms caused by the poisoning. If your pet receives treatment within one hour of ingestion and is showing no symptoms of cardiovascular anomalies your veterinarian may induce vomiting. If this is performed it will be done with caution as it can increase the risk of cardiac and central nervous system complications. In cases where emesis is contraindicated, a gastric lavage may take place. In both cases, the stomach contents should be examined for yew leaves in order to confirm diagnosis. 

If your pet is symptomatic or has consumed yew over an hour prior to seeing the veterinarian, induced emesis is contraindicated. Instead activated charcoal may be administered. This acts as an absorbent in the gastrointestinal system; there is evidence that suggests this may be an effective treatment. To prevent vomiting your dog may be given an antiemetic such as metoclopramide intravenously or subcutaneously.

Unfortunately, the cardiac arrhythmias caused by Japanese yew poisoning are difficult to control.  Your veterinarian may decide to administer atropine sulfate to counteract the cardio-toxic effects of yew poisoning. This is most effective if done soon after consumption.  This will be done with caution as it can increase the risk of myocardial hypoxia and dysfunction.

Following the exposure, it is vital that your dog revisit the veterinarian periodically for electrocardiographic monitoring. This is important even in cases where the dog has not displayed symptoms. To reduce cardiac stressors and the risk of triggering cardiac arrhythmias, exercise, transportation, and excitement should be avoided. To prevent a repeated poisoning, it is vital to ensure all Japanese yew is not accessible to your pet. As dried yew plant material continues to be toxic for months after felling, it is vital that the plant material is completely removed from the property.