Hemlock Poisoning in Dogs

Hemlock can refer either to Conium maculatum, commonly known as poison hemlock, or to the four plants in the Cicuta family, known collectively as water hemlock. The toxins in both plants are dangerous to many animals, including canines. Contrary to what the names may suggest, the water hemlock is the more likely of the two to be lethal even when smaller amounts are ingested. If you suspect your pet ate either of these perennial herbs it is imperative to contact your veterinarian immediately for further treatment options and to start supportive therapy measures.

The two types of plants commonly known as hemlock, while unrelated, are both quite toxic to animals and humans. If your pet ingests either type of hemlock, contact your veterinarian immediately.

Although the toxins in both types of hemlock affect the central nervous system, they do so in slightly differing ways. The signs of water hemlock poisoning can include:

• Abnormal nervousness
• Coma
• Excessive drooling
• Frenzied movement 
• Frothing
• Increased temperature
• Muscle twitching
• Panting
• Pupil dilation
• Rapid pulse
• Rolling eyeballs
• Severe abdominal pain
• Sudden death
• Tremors
• Violent convulsions
• Vomiting

Signs of toxicity from poison hemlock can include:

• Ataxia, especially lower and hind limbs
• Bloody stools
• Coma
• Convulsions
• Excessive drooling
• Frequent urination
• Inability to breathe
• Lack of coordination
• Pupil dilation
• Rapid, weakened pulse
• Respiratory paralysis
• Stimulation followed by depression
• Sudden death
• Trembling
• Weakness

Types

Both types of hemlock are herbaceous flowering plants with purple spotted hollow stems and tight clusters of small white flowers on tall stalks. 

Poison hemlock plants are closely related to the carrot family of plants, and they grow wild in all parts of the United States. Its leaves resemble parsley leaves and it has a single tap root. It is referred to by several common names, including: 

• Carrot fern
• Devil’s bread
• Devil’s porridge
• Poison parsley
• Spotted corobane
• Spotted hemlock

The Cicuta genus of water hemlock plants contains four members and all of them are highly toxic. They grow near the shorelines of lakes and of rivers and have branched root systems with multi-chambered rootstocks which contain an oily yellow liquid. They are also known as:

• Cowbane
• Poison parsnip
• Spotted cowbane
• Spotted parsley

Poisoning from Hemlock is more common in livestock than in dogs as dogs are not generally prone to eating flowering plants. That being said, some dogs will put anything in their mouths, so fatal poisonings have occurred. The toxins in the two types of plants known as hemlock are quite different from one another. 

Poison hemlock, or Conium maculatum, contain piperdine alkaloids such as coniine that cause disruptions to the central nervous system. Coniine has a chemical structure that is similar to nicotine and disrupts the connection between the motor neuron and the muscle fiber causing paralysis. Deaths from poison hemlock are generally asphyxiation deaths caused by the paralysis of the respiratory system. 

Water hemlock, from the Cicuta genus of plants, contains a poisonous compound called cicutoxin. Cicutoxin causes over excitability of the central nervous system which results in violent spasms and seizures as well as disruptions to the rhythm of the heart. Deaths that occur from water hemlock usually occur quickly and are usually due to either respiratory failure or ventricle fibrillation caused by the convulsions.

If you believe your pet has ingested parts of either of these plants do not hesitate to contact your veterinarian. If you see your pet consuming either hemlock plant, identification may be all that is required for diagnosing the origin of your pet’s difficulty. As the two plants look similar to each other and to several other varieties of plants, a sample of the plant may be particularly helpful in this instance. Due to the speed with which the symptoms can become deadly, treatment is often begun even before a diagnosis is proven. Once the animal is somewhat stabilized, a biochemistry profile, complete blood count, and urinalysis are likely to be completed to detect the toxin responsible in the blood or urine. A definitive diagnosis of this poison is often made during necropsy as poison hemlock can cause death in an hour or two, and water hemlock has sometimes been fatal in as little as fifteen minutes.

Prognosis is determined by the amount ingested, the size of the animal, and the speed at which treatment is started, but in most cases, the outcome is guarded to poor. No antidote is available for either toxin so treatment will mainly be symptomatic and supportive. Supportive measures such as IV fluids to keep hydrated and early gastric decontamination (followed by administration of activated charcoal) may be the difference between recovery and death. These measures are frequently initiated immediately upon admission to the veterinary hospital, based on the signs and symptoms that are showing. Stress should be avoided for the patient, as it can hasten the development of symptoms. Intubation and mechanical ventilation may help manage the respiratory paralysis or depression that these chemicals may cause. Intravenous administration of benzodiazepines or barbiturates may be used to help control convulsions, especially in the event of poisoning by the water hemlock.

Even with prompt medical intervention the prognosis from ingestion of either of these toxins is guarded. With poison hemlock, if the toxicity does not end up being lethal most patients recover completely and spontaneously within just a day or two. Water hemlock has an even grimmer prognosis than poison hemlock and canines that recover may suffer from further damage to the heart and skeletal muscle. Depending on the length and severity of the reaction to the poison, the damage may be either temporary or permanent. Your pet may be disoriented and confused from lingering effects of the toxin when they return home, so a calm, quiet atmosphere and ready access to appropriate food and water may help speed recovery.