Toxic Weed - Water Hemlock
Posted: June 7, 2011
WATERHEMLOCK - Cicuta species - Maculata (East)
Native perennial herbs 2-10 feet tall; stem stout, hollow, often purple streaked; base of stem below ground ("root-stock") has horizontal plates crossing the hollow central cavity and containing a large concentration of the poison; leaves alternate, sheathing the stem, 2-3 times pinnately compound; flowers small, white, in compound umbels.
Description. Water hemlock, a member of the Umbelliferae family, is characterized by large terminal inflorescences that radiate from a central point, hollow, purple-streaked stems and leaves with veins that end in the notches of the serrations. The bundle of roots somewhat resembles a cluster of small sweet potatoes. The cut surface of the tuber has many cross striations or a matrix of compressed nodes and internodes that exude a yellow oily substance with the odor of parsnip. The plant grows throughout North America and is found near streams or in swampy or wetland areas. The toxin is a resinoid known as cicutoxin. Cicutoxin is present mainly in the roots and base of the stem. Roots are readily pulled out of the soil by grazing animals when the soil is soft and damp. Cicutoxin is believed to have an action similar to that of picrotoxin. Picrotoxin is a GABA antagonist which prevents inhibitory inward chloride currents in the CNS resulting in CNS stimulation and seizures. As little as 8 ounces of water hemlock may be lethal to cattle or horses.
Clinical signs. Water hemlock toxicosis is characterized by the acute onset of violent tetanic seizures that resemble strychnine poisoning. Salivation is followed by muscle twitching that rapidly progresses to seizures, champing of the jaws, coma, and death. With damage to heart and skeletal muscle, may see increases in serum AST and LDH if the animal survives for a period of time.
Lesions are indistinctive. Prolonged or severe seizures can cause severe muscle changes including myofiber vacuolation, degeneration and fibrosis in the heart and myofiber contraction bands and necrosis in skeletal muscle. Treatment is usually of little value because of the rapid course and extreme toxicity of water hemlock. However, in sheep, it has been shown that the intravenous administration of sodium pentobarbital at the onset of the first seizure will prevent mortality following administration of 1.5 to 2.5 times the normally lethal dose. This plant is considered to be one of the most toxic plants in the United States since so little of it needs to be consumed to cause death. Cattle are the primary species affected, hence the name "cowbane". Animals have been poisoned by drinking water that had been contaminated with trampled water hemlock roots.