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Yew poisoning
Synonym(s): Taxus spp., taxine, alkaloids, sudden death, cardiac
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.
Geographic incidence
- Taxus spp. (yew) are evergreen trees or shrubs that can be found in many countries across the world.
- There are a variety of yew species, such as the European/English yew (Taxus baccata), Japanese yew (T. cuspidata), Chinese yew (T. chinensis), western/pacific yew (T. brevifolia), American yew (T. canadensis), Hicks yew (T media) and Florida yew (T floridana).
- All species of yew are toxic following ingestion, although the toxicity varies with the species.
Age predisposition
- Calves feeding from their mothers may show toxicity whilst their dams appear asymptomatic.
Breed/Species predisposition
- None
Public health considerations
- May have food safety implications for meat and milk.
Cost considerations
- There are obvious production losses associated with fatalities.
- Animals requiring veterinary attention will result in increased veterinary fees for the farmer.
- There may also be cost implications associated with the management of any food safety issues.
Special risks
- Seasonality:
- Poisoning can occur at any time of the year.
- However, the season and environmental conditions can affect alkaloid levels and the toxicity of the plant. It has been suggested that the toxicity of mature leaves and the plant in general is greater in the wintertime.
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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Outcomes
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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
- Waine K, Busin V & Strugnell B (2019) Getting the Most out of On-Farm Post-Mortems: A Guide for Veterinary Surgeons. AHDB, UK. Website: https://ahdb.org.uk.
- 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.