Bovis ISSN 2398-2993

Water hemlock poisoning

Synonym(s): Cicuta virosa, Cicuta bulbifera, Cicuta douglasii, Cicuta maculata

Contributor(s): Nicola Bates , Mike Reynolds

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Introduction

  • Cause: ingestion of Cicuta species.
  • Signs: gastrointestinal and neurological, particularly convulsions. 
  • Diagnosis: based on history, clinical signs and access to the plant material. 
  • Treatment: Supportive.
  • Prognosis: good if there are only mild signs and survival beyond 8 hours; poor in animals with pronounced neurological signs and convulsions. 

Pathogenesis

Etiology

  • Cattle will eat water hemlock readily, particularly new growth although this may be tolerated due to low concentrations of toxins.
  • The concentration of cicutoxin varies throughout the year. It is present in greatest concentration between autumn and early winter, and is found mainly in the yellow oily juice of the roots. 
  • In spring the concentration in leaves and stems increases to concentrations sufficiently high to prove fatal, if ingested in sufficient quantity.  
  • Most cases of poisoning occur in the early spring, when other plants may be unavailable or less attractive. The tuber is palatable and also most toxic in early spring. 
  • As the plant grows toxicity decreases until the flowers and seeds develop; deaths have been reported from ingestion of mature umbrels and fruits. Mature leaves in late spring and summer are less hazardous and poisoning generally only occurs in these seasons if the tubers are consumed. 
  • Wet weather may make water hemlock roots more accessible to animals, leading to episodes of poisoning. In early spring the roots may be partially above ground due to winter frost and ice and may be available when other plants have little material available for forage.

Predisposing factors

General

  • Roots may be exposed following wet weather.
  • Grazing along water courses.
  • Lack of availability of other vegetation.

Pathophysiology

  • All Cicuta species appear to be similar in toxicity. 
  • All parts of the plant are toxic, particularly the root. 
  • The main toxin is cicutoxin, a polyacetylene alcohol. Another compound, cicutol, an alcohol, is relatively non-toxic as demonstrated in a mouse bioassay.  There may also be other substances present in the plant that are equally or more toxic that cicutoxin. 
  • The concentrations of cicutoxin and other components vary with geographical location and season. 
  • The exact mechanism of poisoning is unknown. 
  • Cicutoxin affects Na+ and K+ channels and delays repolarisation. Prolongation of the action potential at excitatory synapses could promote excitatory activity. 
  • Cicutoxin is a powerful CNS stimulant (having similar actions to strychnine) that blocks gamma-amino butyric acid A (GABAA) receptors causing neuronal depolarisation resulting in grand mal convulsions and death. 
  • Cicutoxin may also have cardiopulmonary effects. 

Timecourse

  • Signs may occur suddenly, usually within 15-60 minutes, death can occur quickly (within 15 minutes) or up to 8 hours after ingestion. 
  • Animals may be found dead with evidence of a violent terminal struggle. 
  • Recovery may take 4-5 days. 

Epidemiology

  • Cicuta poisoning in cattle occurs mainly in North America and Europe.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMed Resources.
  • Panter K E, Gardner D R, Stegelmeier B L, Welch K D & Holstege D (2011) Water hemlock poisoning in cattle: Ingestion of immature Cicuta maculata seed as the probable cause. Toxicon 57 (1) pp157-161.
  • Uwai K, Ohashi K & Takaya Y (2000) Exploring the structural basis of neurotoxicity in C(17)-polyacetylenes isolated from water hemlock. Journal of Medicinal Chemistry 43, pp 4598-4515.
  • Wittstock U, Lichtnow KH & Teuscher E (1997) Effects of cicutoxin and related polyacetylenes from Cicuta virosa on neuronal action potentials: a comparative study on the mechanism of the convulsive action. Planta Medica 63 pp 120-4.
  • Panter K E, Keeler R F, Baker D C (1988) Toxicoses in livestock from the hemlocks (Conium and Cicuta spp.). Journal of Animal Science 66 (9) pp 2407-13.
  • Smith R A & Lewis D (1987) Cicuta toxicosis in cattle: case history and simplified analytical method. Veterinary and Human Toxicology 29 (3) pp 240-1.
  • Völker H, Schulz O, Albrecht K & Siering W (1983) Poisoning by cowbane (Cicuta virosa) in fattening bulls. Monatshefte für Veterinärmedizin 38, pp 11-13.
  • Grundy H F & Howarth F (1956) Pharmacological studies on hemlock water dropwort. British Journal of Pharmacology and Chemotherapy 11 (3) pp 225-30.
  • Anet B, Lythgoe M H, Silk S & Trippett S (1953) Oenanthotoxin and cicutoxin. Isolation and structures. Journal of the Chemical Society 66 pp 309-322.
  • Jenkins L & Jackman E R (1941) Water hemlock. Oregon Agricultural Experiment Station Extension Bulletin 559, 4 pages.
  • Fleming C E, Peterson N F (1920) The poison parsnip or water hemlock (Cicuta occidentalis). University of Nevada Agricultural Experiment Station Bulletin 100 pp 1-23.
  • Hedrick U P (1897) A plant that poisons cattle. Oregon Agricultural Experiment Station Bulletin 46 pp 1-12.

Other sources of information

  • Burrows G E & Tyrl R J (2013) Toxic Plants of North America, 2nd edition. Wiley Blackwell, Ames, Iowa.
  • Panter K E, Gardner D R, Holstege D & Stegelmeier BL (2007) A case of acute water hemlock (Cicuta maculata) poisoning and death in cattle after ingestion of green seed heads. In: Poisonous plants: global research and solutions.  CABI Publishing, Wallingford, pp 259-264.
  • Kingsbury J M (1964) Poisonous Plants of the United States and Canada. Prentice Hall, Inc. Englewood Cliffs, New Jersey.

Organisation(s)

  • ASPCA Animal Poison Control Center: www.aspca.org/pet-care/animal-poison-control, telephone number (888) 426-4435.
  • Veterinary Poisons Information Service (VPIS); www.vpisglobal.com. + 44 (0) 2073 055 055. 


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