Pit Viper Snakebite Poisoning (Crotalid Envenomation) in Dogs

Summary

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 venom of pit vipers is toxic to multiple tissue and cell types throughout the body, making venomous snake bites an emergency. Symptoms of pit viper envenomation fall into two categories:

• local tissue damage near the site of the bite

• systemic symptoms throughout the body

The area around a crotalid bite rapidly swells and becomes red and painful in response to envenomation. Severe envenomation leads to symptoms of life-threatening shock like ataxia, weakness, collapse, pale gums, labored breathing, abnormal bleeding, seizures, and loss of consciousness. 

Rapid administration of antivenin (also known as antivenom) is the best, most effective treatment for crotalid envenomation. Antivenin is expensive and not always accessible in a timely manner.

Depending on the severity of the envenomation and response to antivenin, a dog may also require supportive care like analgesics, IV fluids, and oxygen. Additional interventions such as blood transfusions and repeated surgical wound treatment may be necessary in severe cases.

The prognosis depends on the amount of venom delivered, the size of the dog, the location of the bite, species of snake, vaccination status of the dog, and how quickly treatment was administered after the bite occurred. Most cases have a favorable prognosis when antivenin is administered within four hours of envenomation.

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 include: 

• Pale gums • Irregular, wobbly gait (ataxia) • Difficulty breathing (dyspnea) • Collapse

• Abnormal bleeding • Muscle tremors • Seizures

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

Detailed Characterization

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. 

Dogs vaccinated with the CAT vaccine may have milder symptoms, and symptoms may take longer to appear. This vaccine buys the owner time to seek medical attention for their pet, but does not prevent symptoms.

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 • 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 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.

Is Crotalid Envenomation Common in Dogs?

Pit viper envenomation is common in regions with venomous snakes.

Typical Treatment

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