Equis ISSN 2398-2977

Toxicity: snakebite

Contributor(s): Rosalind Dalefield, Vetstream Ltd

Introduction

  • Cause: envenomation by snakebite.
  • Signs: marked local edema; dyspnea; neurological, circulatory and cytotoxic effects; myonecrosis (maybe secondary clostridial infection); rarely - sudden death.
  • Diagnosis: hematology; season and geographical location; elimination of other causes.
  • Treatment: antivenin, supportive.
  • Prognosis: good - guarded.

Pathogenesis

Etiology

  • Snakebite:
    • Rattlesnake.
    • Copperhead.
    • Water moccasin.
    • Coral snake.
  • The rattlesnake, copperhead and moccasin are known as 'pit vipers'.

Predisposing factors

General

  • Season - snakes more active in warmer months.
  • Thoroughbreds Thoroughbred more susceptible.

Specific

  • Size of horse.
  • Size and age of snake.
  • Species of snake.

Pathophysiology

  • Mortality 10-30%.
  • Bite → local tissue edema, necrosis → secondary bacterial infection, eg with Clostridia  Clostridia spp → myonecrotic wound.
  • Systemic effects include hematotoxicity and neurotoxicity → death about 5 days later.
  • Toxicity varies with species and age.

Venoms

  • Rattlesnake Crotalus spp and other pit vipers:
    • Edemetogenic.
    • Myotoxic: rapid disruption of the plasma membrane, hypercontraction and clumping of the myofilaments, and necrosis of affected skeletal muscle cells.
    • Proteolytic.
    • Hematotoxic → echinocytic, spheroechinocytic and spherocytic red blood cell changes as well as haemorrhagic effects.
  • Coral snake:
    • Neurotoxic - envenomation appears to be very rare in horses.

Bites

  • Most commonly around the face, neck and head, due to curiosity.
  • Other sites include legs and chest.
  • Bite on face:
    • Rapid development of edema → nasal mucosa swells and occludes nares → severe and audible dyspnea.
    • Exudation of blood-stained froth from nose.
    • Eyelids and ears become edematous.

Timecourse

  • Local reaction within minutes.
  • Systemic effects → death within hours to days.

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.
  • Anlen K G (2008) Effects of bites by the European adder (Viper berus) in seven Swedish horses. Vet Rec 162 (20), 652-656 PubMed.
  • Santoro M L et al (1999) Comparison of the biological activities in venoms from three subspecies of the South American rattlesnake (Crotalus durissus terrificusC. durissus cascavella and C. durissus collilineatus). Comp Biochem Physiol C Pharmacol Toxicol Endocrinol 122 (1), 61-73 PubMed.

Other sources of information

  • Bailey E M & Garland T (1997) Appendix 4 - Antidotes for Common Poisons. In: Current Therapy in Equine Medicine. Ed: Robinson N E. W B Saunders. ISBN: 0-7216-2633-5.
  • Fowler M E (1993) Veterinary Zootoxicology. CRC Press. ISBN: 0849367913.
  • Burger C H & Van Gelder G A (1982) Snakebite. In: Equine surgery and medicine. Eds: Mansmann R S, McAllister E S & Pratt P W. American Veterinary Publications. Catalog Card No. 81-70196.


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