Canis ISSN: 2398-2942

Venomous animals of North America

Contributor(s): Rosalind Dalefield, Dawn Ruben

Introduction

Presenting signs

  • Depends on the nature of the venom.
  • Envenomation by crotalid snakes causes pain, swelling, necrosis, shock and clotting disorders.
  • Elapid envenomation leads to weakness, paralysis and CNS depression.
    Black Widow spider venom causes pain, muscle tremors and cramps, and ataxia leading to paralysis.
  • Loxosceles envenomation causes necrosis.
  • Scorpion venom causes clinical signs similar to those in Black Widow envenomation.
  • Ticks of the genus Dermacentor may cause an ascending paralysis Neurology: tick paralysis.
  • Heloderma envenomation leads to pain, shock and CNS depression.
  • Hymenoptera stings Dermacentor variabilis cause pain and swelling, and may cause anaphylactic shock.

Geographic incidence

  • Snakebite occurs in every US state but Maine, Alaska and Hawaii.
  • Distribution of crotalid snakes varies with species.
  • Coral snakes are found in the South and Southwest of the United States.
  • Spiders of the genus Latrodectus are found throughout North America.
  • Spiders of the genus Loxosceles are widespread in North America. The Brown Recluse spider Loxosceles reclusais found in the South from Texas to Florida and in the Midwest.
  • Scorpions are most likely to be encountered in the Southwest and in Mexico.
  • Dermacentor tick distribution varies with species. Dermacentor variabilis Dermacentor variabilis, the American dog tick, is the most common cause of paralysis in domestic pets and is found throughout the USA as well as in parts of Canada and Mexico.
  • Heloderma lizards are found in the Southwestern USA and in Mexico.
  • Hymenoptera are found throughout North America except in the most northerly parts of Canada.

Cost considerations

  • May be expensive.
  • Some antivenom is expensive and not likely to be stocked in many veterinary practices.
  • Treatment for severe complications can be expensive.

Pathogenesis

Etiology

  • Crotalid venoms contain a wide variety of lytic enzymes and nonenzymatic proteins. Effects include proteolysis leading to necrosis, hemorrhage, shock and hypotension. Neurotoxic componenets are present in some crotalid venoms. Disseminated intravascular coagulation Disseminated intravascular coagulation may occur.
  • Coral snake venom is primarily neurotoxic leading to depression, weakness, paralysis, hypotension and respiratory distress.
  • Latrodectus venom is primarily neurotoxic, interfering with neurotransmission and neuromuscular function, causing pain, ataxia, muscle tremors, muscle cramping and restlessness, and ultimately fatal paralysis. Nausea, vomiting and diarrhea are also common.
  • Loxosceles bites in domestic pets typically lead to an indolent ulcer that takes a long time to heal. Systemic effects are rare but may include hemolytic anemia with hemoglobinuria, fever, nausea and weakness.
  • Scorpion venoms are complex, containing a variety of enzymes and neurotoxins. Reported effects in pets include parasympathomimetic syndrome, skeletal muscle stimulation, hypertension and respiratory failure. Cranial nerve dysfunctions occur in human beings.
  • The toxin responsible for tick paralysis appears to interfere with acetylcholine synthesis or release at neuromuscular endings.
  • Heloderma venom is complex including hydrolytic enzymes and a neurotoxin. Heloderma lizards typically hang on and chew when they bite, causing local tissue damage. Systemic signs in the dog include hyperpnea, emesis, polyuria, salivation and lacrimation.
  • Hymenoptera venoms are a complex mixture of toxic chemicals. Locally there is pain and swelling. Systemic effects may include cardiovascular and respiratory collapse. CNS depression, nerve dysfunction and severe gastrointestinal effects have been reported in the dog. Anaphylatic shock may also occur.

Timecourse

  • 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 hours 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 hours.
  • Onset of clinical signs of Latrodectus envenomation occurs within 8 hours of the bite. In dogs, signs of restlessness may diminish within 10-20 hours and signs of paralysis may then occur.
  • Loxosceles bites typically take several days to become evident but may take months to heal.
  • Scorpion stings are painful and onset of clinical signs is generally rapid.
  • Tick paralysis is gradual in onset.
  • Heloderma bites are intensely painful and local trauma is immediately apparent. It may be necessary to pry the lizard off the patient.
  • 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 and Talcott. Saunders.
  • Peterson M E (2001) Snake Bite: Pit Vipers and Coral Snakes. In: Small Animal Toxicology. Eds Peterson and Talcott. Saunders.
  • Peterson M E & McNalley J (2001) Black Widow Spider Envenomation. In: Small Animal Toxicology. Eds Peterson and Talcott. Saunders.
  • Peterson M E & McNalley J (2001) Brown Spider Envenomation. In: Small Animal Toxicology. Eds Peterson and Talcott. Saunders.
  • Murray E Fowler (1992) Veterinary Zootoxicology. CRC Press.
  • Oehme F W (1987) Clinical Toxicology in Small Animals. Proceedings # 103 Veterinary Clinical Toxicology University of Sydney Postgraduate Committee in Veterinary Science 1987.

Organisation(s)


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