Pit Viper Snakebite Poisoning (Crotalid Envenomation) in Dogs

Venomous snakes are found in many locations throughout the world, however most reports of dog envenomation occur in North America and Australia. Pit vipers are a family of venomous snakes also referred to as crotalids. North American species of pit vipers include the cottonmouth (water moccasin), copperhead, and a variety of rattlesnakes, all of which have been reported to cause serious envenomation of dogs.

The severity of crotalid envenomation varies widely depending on many factors, including:

• Size of the affected dog
• Amount of venom delivered
• Location of the bite
• Vaccination status of the dog
• Species of snake

If the snake delivers only a small amount of venom, symptoms may be limited to local tissue damage. The effects of venom may be proportionate to the size of dog, with smaller dogs being more severely affected. Bites to the chest or abdomen have a higher mortality rate than bites to the head or limbs.

Snake bites are considered an emergency. Severe envenomation causes widespread cellular damage throughout the body and life-threatening shock results. If the dog survives the initial shock, destruction of local tissue develops and creates a large wound. Dogs with suspected venomous snake bites need immediate veterinary care. Rapid access to antivenin is the priority for treatment, so transportation should not be delayed for any reason, including initiating first aid efforts like ice packs or applying a tourniquet.

The Crotalus Atrox Toxoid (CAT) vaccine can help reduce the damage caused by venom, and slow the onset of symptoms. Keeping a dog up to date on CAT vaccinations is a preventive measure and is not a replacement for emergency care when a dog has been envenomated by a pit viper.

Pit viper envenomation in dogs occurs when a dog receives a bite from a pit viper that delivers venom.

Pit vipers found in North America include:

• Several species of rattlesnakes
• Cottonmouth (water moccasin)
• Copperheads

Severe systemic symptoms are usually associated with species of crotalids that produce a neurotoxin which impairs muscle contraction. Neurotoxin producing crotalids include:

• Mojave rattlesnake
• Tiger rattlesnake
• Neotropical rattlesnake
• Bushmaster

Pit vipers do not always deliver venom when they bite. The snake has control over how much venom (if any) to deliver. The severity of symptoms produced following a pit viper envenomation event depends on many variables, but the amount of venom injected is a primary factor.

The symptoms associated directly with the wound itself include:

• Dark red to brown skin
• Significant swelling
• Dark red fluid oozing from the wound
• Pain

When the venom damages tissues and cells throughout the body, symptoms progress.

Symptoms usually appear quickly, but it can take up to 8 hours for symptoms to appear after a pit viper envenomation event.

If the snake bite was witnessed, the diagnosis is self-evident. If the bite was not witnessed but the typical clinical signs are present, crotalid envenomation is suggested by specific changes in:

• Routine screening blood tests (complete blood count and serum chemistry profile)
• Blood clotting profiles
• Urinalysis
• Blood pressure

Timely IV administration of antivenin is the priority when treating crotalid envenomation, ideally within the first four hours following the bite.

Supportive care for a dog in shock as a result of crotalid envenomation includes:

• IV fluids
• Oxygen
• Analgesics (painkillers)

Once the dog is stable, treatment of the wound is the next priority. In severe envenomations, tissue death will continue over several days, so wound management is an ongoing process. Multiple surgeries and blood transfusions may be necessary.

The outcome of a snake bite depends on the species of snake, location of the bite, amount of venom delivered, size of the dog, and how rapidly treatment was implemented.

The prognosis for pit viper bites is generally favorable if antivenin is administered in the first four hours following envenomation. Careful monitoring for adverse reactions during antivenin administration is critical.

In some cases, severe local tissue damage may lead to further complications. For example, the area of the bite wound may lose function or need amputation.

Snakebite envenomation is prevented by avoiding contact with poisonous snakes. Keeping up to date on CAT vaccination can help prevent severe symptoms or death if an envenomation occurs, but emergency medical attention is still required whether a dog is vaccinated or not.

Pit viper envenomation is common in regions with venomous snakes.

The best, most effective treatment for crotalid envenomation is antivenin/antivenom, ideally administered within four hours of the bite.

Supportive care is also provided as needed, including:

• Wound care
• IV fluids
• Oxygen
• Analgesics
• Sedation