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Yew poisoning

obovis
Contributor(s):

Nicola Bates

Paul Wood

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Synonym(s): Taxus poisoning


Introduction

  • Cause: taxus spp. contain taxine alkaloids which are cardiotoxins. Most cases occur due to accidental ingestion of hedge trimmings or by grazing on yew plant material. Livestock may be exposed through: 
    • Garden waste containing clippings of yew plant material discarded onto grazing pasture.
    • Yew tree or shrub felling/pruning/trimming in or around grazing pasture.
    • Livestock gaining access to private gardens, churchyards or woods containing Taxus spp..
  • Signs:
    • Acute toxicity: sudden death.
    • Subacute toxicity: ataxia, bradycardia, dyspnea, tremors, collapse and death.
  • Diagnosis: history of exposure, visual presence of Taxus spp. material in gastrointestinal tract (GIT) at necropsy, identification of Taxine alkaloids in rumen contents.
  • Treatment: supportive care and removal from the source of Taxus spp..
  • Prognosis: mortality can be high.  Animals may be found dead.

Pathogenesis

Etiology

  • All species of yew contain toxins, called Taxine alkaloids.  
  • The various species of Taxus can contain different types and amounts of alkaloids, hence the toxicity of the plant varies with the different species of yew.  
    • The English yew (T. baccata) and the Japanese yew (T. cuspidata) are recorded as the species of greatest toxicity; these two yew species contain large amounts of the Taxine alkaloids Taxine A and Taxine B when compared to, for example, the pacific/western yew (T. brevifolia) in which small quantities of Taxine alkaloids are found. 
    • The type of alkaloids present in the different yew species can influence the clinical picture and type of effects observed.
  • Yew plant material is still toxic after drying.  It has been suggested it may be more toxic than fresh Taxus spp. material.
  • Parts of the plant ingested:
    • All parts of the Taxus spp. are toxic, except the flesh of the 'fruit' (the coloured aril).
    • Older, mature plant material has higher levels of alkaloids compared to young plant material or new shoots.  Stems have been reported to be more toxic than the leaves.

Predisposing factors

General

  • It has been suggested that male plants are more toxic in comparison to female specimens of yew species.
  • Time of the year: the highest level of Taxines occur in the yew plant at wintertime.
  • The amount of Taxus spp. plant material ingested. The more material ingested, the more severe the toxicity picture.  
  • Individual animal grazing behaviours and availability of, and access to, other forage: 
    • Yew is not thought to be palatable and is more likely to be ingested when it has been mixed with other more palatable foods, such as hay or grass. 
    • Incidents of yew poisoning in cattle may occur in malnourished animals, or when availability of other forage/fodder is limited.

Pathophysiology

  • The toxic component is Taxine, which is a complex mixture of alkaloids, such as Taxine A, B and C.
  • Numerous alkaloids have been isolated from the various species of Taxus.
  • The main alkaloid toxins are Taxine A and Taxine B, with Taxine B being more toxic than Taxine A and more prevalent in the Taxus species.
  • Taxines are quickly absorbed and metabolised in the liver.  Elimination occurs via the kidneys.
  • Taxines are cardiotoxins.  
  • The Taxine alkaloids interfere with the ion channels in the myocardial cells (i.e. calcium and sodium channels). Their main action is antagonism of calcium channels, which reduces atrio-ventricular (AV) conduction, causing arrhythmias, bradycardia and cardiac arrest. 
  • Taxine B has negative inotropic effects and causes hypotension as a result of arterial vasodilation.
  • In comparison to Taxine B, Taxine A has less effect on the heart rate and AV conduction.
  • The Taxines may also effect involuntary muscle action.  In experimental animal studies uterine contraction and intestinal relaxation was observed, as well as reduced peristalsis in the GIT. 
  • In addition to the Taxines, Taxus species contain an irritant volatile oil which is present throughout the plant and can cause gastrointestinal irritation and diarrhoea in cattle with subacute toxicity. 

Timecourse

  • The onset of clinical signs can vary, during which time the exposed animal may appear clinically well. 
  • Sudden death is common.  
  • Death can occur within 2-36 hours, usually within 24 hours, depending on the quantity of Taxus spp. material ingested.  
  • In ruminants the onset of effects may be delayed. Death could be delayed for up to 48 hours in cattle, which may appear asymptomatic in the interim period.
  • Cases showing a prolonged clinical picture may also occur, with clinical effects observed days post initial exposure.  

Diagnosis

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Treatment

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Prevention

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed And VetMedResource
  • Burcham G N, Becker K J, Tahara J M, Wilson C R & Hooser S B (2013) Myocardial fibrosis associated with previous ingestion of yew (Taxus spp.) in a Holstein heifer: evidence for chronic yew toxicity in cattle.J Vet Diag Invest 25 (1), 147-152.
  • Sula M J M, Morgan S, Bailey K L, Schumpert M & Njaa B L (2013) Characterization of cardiac lesions in calves after ingestion of Japanese yew (Taxus cuspidata). J Vet Diag Invest 25 (4), 522-526 PubMed.
  • Cope R B (2005) The dangers of yew ingestion. Vet Med 100 (9), 646- 650.
  • Wilson C R, Sauer J M & Hooser S B (2001) Taxines: a review of the mechanism and toxicity of yew (Taxus spp.) alkaloids. Toxicon 39 (2-3), 175-185 PubMed.
  • Panter K E, Molyneux R J, Smart R A, Mitchell L & Hansen S (1993) English yew poisoning in 43 cattle. JAVMA 202 (9), 1476-1477 PubMed.
  • Ogden L (1988) Taxus (yews) – a highly toxic plant. Vet Hum Toxicol 30 (6), 563-564 PubMed.
  • Veatch J K, Reid F M & Kennedy G A (1988) Differentiating yew poisoning from other toxicosis. Vet Med 83, 298-300.
  • Casteel S W & Cook W O (1985) Japanese yew poisoning in ruminants. Mod Vet Pract 66, 875-877.
  • Miller R W (1980) A brief survey of Taxus alkaloids and other taxane derivatives. J Natural Prod (Lloydia) 43 (4), 425-437
  • Thomson G W, Barker I K (1978) Japanese yew (Taxus cuspidata) poisoning in cattle. Can Vet J 19 (11), 320-321 PubMed.
  • Alden C L, Fosnaugh C J, Smith J B & Mohan R (1977) Japanese yew poisoning of large domestic animals in the Midwest. JAVMA 170, 314-316 PubMed
  • Anon (1972) Yew poisonous. Anim Nutr Health 5, 15.

Other sources of information

  • EMA (2015) CVMP Assessment Report Regarding the Request for an Opinion Under Article 30(3) of Regulation (EC) No. 726/2004 in Relation to the Potential Risk for the Consumer Resulting from the use of Lidocaine in Food Producing Species. [online] Last accessed on 21st November 2017. Available at: www.ema.europa.eu/
  • Smith B P (2015) Large Animal Internal Medicine. 5th edn. Eds: B P Smith. Elsevier Mosby.
  • Plumb D C (2013) Atropine. Plumb Online. [online] Last accessed on 21st November 2017. Available at www.plumbsveterinarydrugs.com.
  • Baskin S I, Czerwinski S E, Anderson J B & Sebastian M M (2007) Toxic Plants Affecting the Cardiac System – Taxus spp. In: Veterinary Toxicology, Basic and Clinical principles. 1st edn. Ed: Gupta R C. Elsevier Inc. pp 199.
  • Wilson C R and Hooser S B (2007) Toxicity of Yew (Taxus spp) Alkaloids. In: Veterinary Toxicology, Basic and Clinical principles. Ed: Gupta R C. Elsevier Inc. pp 929-935.
  • Anon (2006) Diseases Associated with Toxins in Plants, Fungi, Cyanobacteria, Plant-Associated Bacteria and Venoms in Ticks and Vertebrate Animals – Taxine. In: Veterinary Medicine – A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goats. 10th Edn. Eds: Radostits O M, Gay C C, Hinchcliff K W & Constable P D.  Saunders, Elsevier. pp 1893.
  • Orbell G (2006) Fatal Yew Toxicity in Beef Heifers. In: Proceedings of the Society of Sheep and Beef Cattle Veterinarians of the NZVA. pp 117-121.
  • Casteel S W (2004) Taxine Alkaloids. In: Clinical Veterinary Toxicology. Ed: Plumlee K H. Mosby. pp 379-381.  
  • Cooper M R, Johnson A W (1998) Poisonous Plants and Fungi in Britain. 2nd edn. The Stationer Office, UK.
  • Hare W R (1998) Yew (Taxus spp) Poisoning in Domestic Animals. In: Toxic Plants and Other Natural Toxicants. Eds: Garland T & Barr A C. CAB International. pp 78-80.
  • EMA (1995) Heptaminol: Summary report - Committee for Veterinary Medicinal Products. [online] Last accessed 21st November 2017. Available from: www.ema.europa.eu
  • Andrews A H & Humphreys D J (1982) Taxus Baccata. In: Poisoning in Veterinary Practice. 2nd edn. NOAH, UK. pp 103. 
  • Kingsbury J M (1964) Taxaceae. In: Poisonous Plants of the United States and Canada. 3rd edn. New Jersey. pp 121-123.

Organisation(s)

  • Tiffany Blackett. Veterinary Poisons Information Service (VPIS), London. UK.

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