Snakebite Envenomization

My dog has been bitten by a snake. Will he die?

It depends on the species of snake. There are approximately 3,000 species of snakes in the world with fewer than 500 venomous species. In North America, there are about 25 species of venomous snake, broken up into two classifications:

Pit vipers: Including copperheads; cottonmouths (also known as water moccasins); and rattlesnakes (many species, including black-tailed, diamondback, Massasauga, Mojave, pygmy, red diamond, ridge-nosed, rock, sidewinder, speckled, tiger, timber, twin-spotted, and western) 

Elapids: Coral snakes (Arizona, eastern, Texas, and western) 

What are the signs of snakebite?

In dogs bitten by a non-venomous snake, swelling and bruising around the bite are the most common clinical signs. In some cases, paired puncture wounds from the fangs may still be visible in the center of the wound. The bite may be very painful and become infected if not treated by a veterinarian. The swelling won’t increase much, unless infection develops. Most swelling resolves within 48 hours in uncomplicated cases.

"If your dog has been bitten by a snake, contact a veterinarian immediately for recommendations."

In dogs bitten by a venomous snake, clinical signs vary based on the species of snake. Generally, there is extensive swelling that often spreads quickly. Bleeding or a bloody discharge often occurs at the site of the bite. Puncture wounds from the fangs may not be visible due to rapid swelling or the small mouth size of young or small snakes. 

Clinical signs may vary depending on the size of the dog, the bite location, and other factors. If your dog has been bitten by a snake, contact a veterinarian immediately for recommendations.

The venom of most North American pit vipers (rattlesnakes and cottonmouths) contains toxic substances that produce local and body-wide effects. Around the bite, there may be pain, swelling, inflammation, tissue breakdown, and hemorrhage. Body-wide effects may include:

• Shock with low blood pressure
• Disturbances in the blood’s pH
• Abnormal bleeding: bleeding from the nose or gums, or blood in the stool (may be black)
• Vomiting and diarrhea
• Difficulty breathing
• Stumbling while walking
• Seizures
• Coma

The venom of most North American pit vipers causes only minor muscle and neurological disease, although Mojave and eastern diamondback rattlesnake venom may cause serious neurological problems.

Coral snake venom mostly contains components that are toxic to the neurological system, which result in neuromuscular damage and, in some cases, difficulty breathing or bleeding disorders similar to pit viper venom. These signs can take several hours to appear. There are often minimal symptoms and signs at the bite site.

How is snakebite envenomization diagnosed?

Diagnosis is primarily made based on medical history and clinical signs. If the type of snake is unknown, diagnosis and treatment will be directed at the clinical signs present.

What first aid treatment should I do on my way to the veterinarian?

First aid should aim to reduce the rapid spread of venom in the body.

• Muzzle your dog to avoid being bitten. Snakebites are painful, and your dog may try to bite out of discomfort.
• Carry your dog rather than allowing them to walk, if possible.
• Keep your pet quiet and warm on the journey to the veterinarian.
• Try to keep the bitten area at or below the level of the heart to reduce blood flow to the area.

How is snakebite envenomization treated?

Venomous snakebites are medical emergencies and require immediate attention. Before treatment begins, your veterinarian must determine whether the snake is venomous and whether envenomization has occurred. Fortunately, a venomous snake may bite and not inject venom. These are called dry bites, and they occur in about 20% to 30% of pit viper bites and in about 50% of coral snakebites.

When no envenomization occurs, or if the bite is inflicted by a non-venomous snake, the bite may be treated as a puncture wound. Treatment may include wound cleaning, anti-inflammatory medications, and possibly antibiotics if your veterinarian feels they are warranted.

The treatment of venomous snakebites depends on the type of snake, but typically includes the use of antivenin (also called antivenom) specific to the snake. Antivenin is composed of antibodies that bind and neutralize venom. Its efficacy depends on how quickly it is administered after the snake bite.

Rattlesnake envenomization is immediately life-threatening and prompt medical assistance must be sought. Coral snake bites are also life-threatening and require immediate administration of appropriate antivenin. Cottonmouth envenomization may require antivenin treatment in severe cases. Along with antivenin therapy, treatment is often needed to address specific clinical signs, such as shock or respiratory distress.

What is the prognosis for a dog bitten by a snake?

The prognosis depends on several factors, including:

• Size and species of the snake
• Amount of venom injected
• Number of bites
• Location and depth of the bite (bites to the head and body tend to be more severe than bites to the legs or paws)
• Age, size, and health of the dog
• Time elapsed before treatment
• The dog's individual susceptibility to the venom

The location of the bite is important. Swelling from bites around the muzzle and face can lead to breathing difficulties due to obstruction of the airway. Fortunately, several studies have shown a less than 10% chance of death following a viper bite with appropriate treatment.

Copperhead, cottonmouth, and coral snake envenomization cases have a better prognosis for complete recovery than rattlesnake bites.

How can I prevent my dog from being bitten by a snake?

Most snakes try to avoid people and pets. If you see a snake, the best thing to do is avoid it. When out hiking, stay on open pathways and keep away from snake resting places such as holes, logs, or rocky outcrops. Ideally, keep your dog on leash to prevent startling a snake. Since rattlesnakes are nocturnal, try to hike during the daytime, when it is safer. Learn about snakes in your area so you can easily identify the snake and its potential danger.

There is a rattlesnake bite vaccine (Crotalus Atrox Toxoid or CAT) available in the United States. It is designed to help neutralize western diamondback rattlesnake venom; however, effectiveness has not yet been proven in studies and dogs still need veterinary care after a venomous snake bite has occurred. Ask your veterinarian if this vaccine is appropriate for your dog.