• Most venomous snakebites in North America are due to Pit Vipers.
• The Pit Vipers of North America include:
  • Species of rattlesnakes (genus Crotalus)  .
  • Pygmy rattlesnakes (genus Sistrurus).
  • Massasauga (genus Sistrurus).
  • Cottonmouths (genus Agkistrodon).
  • Copperheads (genus Agkistrodon) .
• Cause: snakebite by Pit Viper.
• Signs: extensive swelling and bruising at the site of envenomation, persistent hemorrhage at site of envenomation. Patients are often agitated, excited, painful on presentation and occasionally the patient will present in shock.
• Diagnosis: localized swelling and bruising, usually of the head or distal limbs. Scabbed-over or bleeding puncture wounds in the region of swelling from fang penetration.
• Treatment: specific antivenom and supportive therapy.
• Prognosis: mortality is low if appropriate therapy is initiated within the first 1-4 hours after envenomation, but will vary with venom dose and site of bite.
  Print off the owner factsheet Venomous snake bite in dogs to give to your client.

Presenting signs

• Generally dogs are bitten during the warmer summer months, between April and October.
• Dogs are often bitten on the head   and/or distal limbs resulting in localized swelling. However, snakebites are not always easy to diagnose due to several factors including:
  • The individual victim.
  • Species of snake.
  • Dose of venom administered.
  • The proportion of venom delivered to the subcutaneous, intramuscular, or intravenous tissue compartments.
• It is estimated that nearly 20% of snakebites in humans are "dry" bites, meaning a bite where no evidence envenomation is present.
• Clinical signs associated with snakebites include:
  • Fang marks (sometimes with persistent hemorrhage).
  • Rapid swelling of envenomation site(s).
  • Edema either proximal or distal to the envenomation site(s).
  • Pain in the region of envenomation site(s).
  • Erythema.
  • Petechia.
  • Ecchymosis.
  • Localized tissue necrosis.
  • Vomiting Vomiting (less common).
  • Respiratory distress if there is extensive swelling of the soft tissues associated with the airway.
  • Hypotension, tachycardia and/or arrhythmia.
  • Fever.
  • Bleeding disorders.
  • Neurologic dysfunction including seizures if the snake possesses a neurotoxin.
• Often clients will present their dog after witnessing the pet harassing a rattlesnake on an walk.

Geographic incidence

• Rattlesnakes are found throughout both North and South America in ranges from southern Canada to northern Argentina and Uruguay.
• They are found throughout all of the United States except for Alaska, Hawaii, Maine, and Delaware.
• Because rattlesnakes are cold-blooded animals, they prefer hot arid environments such as the desert, sand hills, grassy planes or rocky hillsides. However, they are present in the Rocky Mountains where the temperatures get quite cold in the winter months. They are also very common in areas where there is an ample supply of rodents.

Age predisposition

• Although there are no studies to support this, young animals are more likely to receive multiple snakebites.
• As a result, young animals are more likely to suffer severe envenomation.

Cost considerations

• Antivenom:
  • Boehringer Ingelheim Antivenin Polyvalent - equine origin, lyphophylized serum whole IgG product, manufactured using venoms from Western Diamondback, Eastern Diamondback, Tropical and Fer de Lance costs the veterinarian approximately $400/vial.
  • CroFab - Crotzlidae Polyvalent Immune Fab - ovine origin, lyophylized serum Fab fragment product, manufactured using venoms from Western and Eastern Diamondback and Pacific rattlesnakes and Copperhead, costs the veterinarian approximately $1000/vial.
  • Venom Vet" - equine origin, non-lyophylized serum Fab2 fragment product, manufactured using venoms from 3 species ofBothrops, South American and Aruba rattlesnakes, costs the veterinarian approximately $295/vial.
  • Crotalid Antivenin, Equine Origin (Lake Immunogenics) - plasma whole IgG product, manufactured using venoms form Western Diamondback, Prairie and Mojave rattlesnakes, costs the veterinarian approximately $150/liter.
• Hyperimmune plasma:
  • RTLR" (Mg Biologics) - equine origin, plasma whole IgG product, manufactured using venoms from Western and Eastern Diamondback, Mojave and Prairie rattlesnakes, costs the veterinarian approximately $110/100 ml.
• Because of the cost, it is unlikely that veterinarians will stock the antivenom unless they are in the south-western United States.

Special risks

• There are several publications in the literature reporting envenomation by rattlesnakes after death (or decapitation).
• Therefore, venomous snakes are still capable of injuring humans and their pets after death.