Pit Viper Snakebite Poisoning (crotalid envenomation) - Dogs - Causes, Treatment and Associated Conditions

Key takeaways

Pit viper snake bites in dogs are caused by a family of venomous snakes also referred to as crotalids. The venom is toxic to multiple tissue and cell types throughout the body.

Symptoms of pit viper envenomation fall into two categories: local tissue damage near the site of the bite, and systemic symptoms throughout the body
The area around a crotalid bite rapidly swells and becomes red and painful
Severe envenomation leads to symptoms of life-threatening shock (ataxia, weakness, collapse, pale gums, labored breathing, abnormal bleeding, seizures, loss of consciousness_
Rapid administration of antivenin (antivenom) is the most effective treatment
Depending on the severity supportive care or additional intervention may be required
The prognosis depends on a variety of factors but most have a favorable prognosis when antivenin is administered within four hours of envenomation

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A closer look: 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.

Risk factors

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.

Possible causes

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.

Main symptoms

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.

Testing and diagnosis

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.

Steps to Recovery

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.

Prevention

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.