Equis ISSN 2398-2977

Toxicity: venomous animals and insects of North America

Contributor(s): Dawn Ruben, Wilson Rumbeiha, Vetstream Ltd

Introduction

Pathogenesis

Etiology

Snakes

  • Crotalid venoms contain a wide variety of lytic enzymes and non-enzymatic proteins:
    • Effects include proteolysis → necrosis, hemorrhage, shock and hypotension.
    • Neurotoxic components are present in some Crotalid venoms; these cause ataxia and paralysis, especially of the respiratory muscles.
    • Disseminated intravascular coagulation Disseminated intravascular coagulation may occur.
    • Usually there is edema and severity of clinical signs depends on the site of the bite.
    • Bites to the head and neck are life-threatening.
    • Horses are obligate nasal breathers and severe edema may cause suffocation through nasal obliteration. 
  • Coral snake venom is primarily neurotoxic → depression, weakness, paralysis, hypotension and respiratory distress:
    • Bites to the head and neck are more life-threatening because of proximity to the brain.
    • Lactrodectus venom is primarily neurotoxic, interfering with neurotransmission and neuromuscular function, through release of acetylcholine and adrenaline; this causes pain, ataxia, muscle tremors, muscle cramping and restlessness and paralysis.
    • Severity of signs depends on both the spider and the horse.
    • Older larger spiders are more likely to have more venom.
    • Location of bite is also another factor.
    • Young healthy victims are likely to be less affected than old predisposed victims. 
  • Loxosceles bites typically → an indolent ulcer (necrotic arachnidism) that takes a long time to heal. Systemic effects are rare but may include hemolytic anemia Anemia: auto-immune hemolytic (AIHA) with hemoglobinuria, fever, nausea and weakness.

Scorpions

  • Scorpion venoms are complex, containing a variety of neurotoxic proteins and non-proteins, eg amino acids, histamine and serotonin.
  • Some contain enzymes others do not. 
  • Envenomation causes release of acetylcholine.
  • Reported effects in pets include parasympathomimetic syndrome, including skeletal muscle stimulation and hypertension. 

Ticks

  • The toxin responsible for tick paralysis interferes with acetylcholine synthesis or release at neuromuscular endings. 

Lizards

  • Heloderma venom is complex including hydrolytic enzymes (phospholipase A2, hyaluronidase) and gilatoxin, a neurotoxin.
  • Heloderma lizards typically hang on and chew when they bite, causing local tissue damage.
  • Although there is potential for envenomation in horses, currently there are no reports.

Bees/wasps/hornets/ants

  • Hymenoptera venoms are a complex mixture of toxic chemicals, including formic acid, enzymes, dopamine, amino acids, etc.
  • Locally there is pain and swelling.
  • Systemic effects may include cardiovascular and respiratory collapse.
  • Multiple bee stings cause frenzy in horses and could cause urticarial reaction Urticaria / angiedema, prostration and hemoglobinuria.

Timecourse

Snakes

  • Crotalid bites are painful and onset of clinical signs is usually rapid but may be delayed for several hours. 
  • Envenomation does not always occur in snakebite.
  • If there is no swelling apparent within 2 h of a Crotalid bite, then envenomation has not occurred. 
  • Coral snake envenomation may be painless, and onset of clinical signs may be delayed for up to 18 h. 
  • Onset of clinical signs of Lactrodectus envenomation occurs within 8 h of the bite. 
  • Loxosceles bites typically take several days to become evident but may take months to heal. 

Scorpions

  • Stings are painful and onset of clinical signs is generally rapid. 

Ticks

  • Paralysis is gradual in onset. 

Lizards

  • Heloderma bites are intensely painful and local trauma is immediately apparent.
  • It may be necessary to pry the lizard off the patient. 

Bees/wasps/hornets/ants

  • Hymenoptera stings cause an immediate reaction.

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

Other sources of information

  • Peterson M E (2001) Poisonous Lizards. In: Small Animal Toxicology. Eds: Peterson & Talcott. Saunders. 
  • Peterson M E (2001) Snake Bite: Pit Vipers and Coral Snakes. In: Small Animal Toxicology. Eds: Peterson & Talcott. Saunders. 
  • Peterson M E & McNalley J (2001) Black Widow Spider Envenomation. In: Small Animal Toxicology. Eds: Peterson & Talcott. Saunders. 
  • Peterson M E & McNalley J (2001) Brown Spider Envenomation. In: Small Animal Toxicology. Eds: Peterson & Talcott. Saunders. 
  • Colahan P T, Merrit A M et al (1999) Equine Medicine and Surgery. 5th edn. Mosby.
  • Murray E F (1993) Veterinary Zootoxicology. CRC Press. 
  • Oehme F W (1987) Clinical Toxicology in Small Animals. In: Proc 103 Vet Clin Toxicol. University of Sydney Postgraduate Committee in Veterinary Science.


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