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Strychnine is an alkaloid extract obtained from the dried ripe seeds of Strychnos nux vomica, a small tree of the East Indies. In the past strychnine was used as an antiseptic, stomach tonic, circulatory stimulant, central nervous system stimulant, and as a medication for the relief of constipation. Strychnine has been replaced by zinc phosphide as a control agent. Strychnine was primarily used in a cracked corn bait to eliminate unwanted bird and rodent populations, but occasionally other wildlife species were inadvertently poisoned. All animals were susceptible to strychnine poisoning, but birds were more frequently affected. Species that have died from strychnine poisoning in Michigan are: rock dove, cardinal, Canada goose, dark-eyed junco, mallard, common grackle, blue jay and house sparrow. Following ingestion, strychnine is rapidly absorbed through all mucous membranes especially the stomach and small intestines and is rapidly eliminated by the kidney and liver.
Clinical Signs and Pathology
The clinical signs of strychnine poisoning relate to its effects on the central nervous system. The first clinical signs include uneasiness, restlessness, anxiety, muscle twitching and stiffness of the neck. The animal is in severe pain and the pupils are dilated. These signs can resemble tetanus, with an increase in spinal reflexes leading to tonic convulsions characterized by sudden contractions of all striated muscles followed by complete relaxation. The animal becomes hypersensitive to external stimuli and the slightest noise or touch can trigger convulsions.
Birds affected by strychnine poisoning exhibit feathers fluffed or held tightly against the body, ataxia, wing droop, salivation, tremors, muscle tenseness, and convulsions. Death occurs as a result of respiratory arrest. No postmortem lesions are observed with the exception of small pinpoint hemorrhages in the lungs resulting from death due to asphyxia. Rigor mortis occurs shortly after death and persists for days. Strychnine poisoning in birds is generally accompanied by the presence of cracked corn in the digestive tract.
A tentative diagnosis can be made based on clinical signs and history. However, a positive diagnosis can only be made by identifying strychnine in the stomach contents and viscera. The drug can be identified by chemical tests and histopathological identification of typical strychnine crystals.
Treatment and Control
Due to the rapid absorption and action of strychnine, treatment is impractical for wildlife, unless found immediately after ingestion. If treatment is desired, it consists of controlling the seizures with intravenous diazepam (Valium R). Once seizures are controlled, unabsorbed strychnine can be removed from the stomach by gastric lavage of tannic acid (strong tea) or potassium permanganate solutions used as chemical antidotes.
In Michigan, wildlife poisonings due to strychnine were infrequent due to its classification as a restricted use pesticide, with use limited to certified applicators. Strychnine treated peanut bait for mole control was removed from the market in the late 1960's due to accidental pet poisonings. Strychnine is a potent poison for all animals including humans.
For questions about wildlife diseases, please contact the Michigan DNR Wildlife Disease Laboratory.