Snakebite Envenomization

By Malcolm Weir, DVM, MSc, MPH; Tammy Hunter, DVM; Ernest Ward, DVM

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 less than 500 venomous species. In North America, there are about 25 species of venomous snakes; the most common include rattlesnakes, copperheads, cottonmouths (also called water moccasins), and coral snakes. Rattlesnakes, copperheads, and cottonmouths are closely related, and are part of the pit viper family of snakes.

Rattlesnakes Copperheads Cottonmouths Coral snakes Banded rock Prairie Broad-banded Eastern Arizona Black-tailed Red diamond Northern Florida Eastern Canebrake Ridge-nosed Osage Western Texas Diamondback (eastern, western) Sidewinder Southern Western Massasauga (eastern, western) Speckled Trans-Pecos Mojave Tiger Mottled rock Timber Pacific (northern, southern) Twin-spotted Pigmy (southeastern, 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, it may still be possible to see the paired puncture wounds from the fangs in the center of the wound. The bite may be very painful and become infected if not treated by a veterinarian. There will be little progression of the swelling unless infection develops. Most swelling resolves within 48 hours in uncomplicated cases.

The clinical signs associated with a venomous snakebite 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. The puncture wounds from the fangs may not be visible due to either the rapid swelling or the small mouth size of young or small snakes.

"The puncture wounds from the fangs may not be visible
due to swelling or the small mouth size of young or small snakes."

The venom of most North American pit vipers (rattlesnakes and cottonmouths) contains toxic protein components, which produce local and body-wide effects. These effects may include local tissue and blood vessel damage, destruction of red blood cells, bleeding or clotting disorders, and lung, heart, kidney, and neurologic defects. Pit viper venom can cause shock, low blood pressure, and disturbances in the pH of the blood. 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 neurologic problems.

Coral snake venom contains mostly components that are toxic to the neurologic system, which result in neuromuscular damage. There are often minimal symptoms and signs at the bite site.

How is a diagnosis of snakebite envenomization made?

Diagnosis is primarily made 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 is aimed at reducing 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.
  • If possible, carry the dog rather than allowing the dog to walk.
  • Keep your pet quiet and warm on the journey to the veterinarian.
  • Try to keep the area bitten at or below the level of the heart to reduce blood flow to the area.

What is the treatment for snakebite envenomization?

Venomous snakebites are medical emergencies requiring immediate attention. Before treatment begins, your veterinarian must determine whether the snake is venomous and whether envenomization occurred. Fortunately, a venomous snake may bite and not inject venom. These are called dry bites and they occur in about 20-30% 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 should be treated as a puncture wound. Non-venomous snakebites are generally treated with wound cleaning, antibiotics and anti-inflammatory medications as indicated.

"The correct treatment of venomous snakebites depends on the type of snakebite."

The correct treatment of venomous snakebites depends on the type of snakebite.

  • Copperhead envenomization is usually treated with a combination of antibiotics and fluid therapy to counter potential hypotension or shock.
  • Rattlesnake and coral snake envenomization is treated with appropriate antivenin (a serum containing antibodies to neutralize the effects of the injected venom) and treatments to counter potential shock.

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.

Treatment to counter shock, low blood pressure, infection and respiratory distress is necessary in most cases of venomous snakebites.

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

The prognosis depends on several factors, including: the size and species of the snake; the amount of venom injected; the number of bites; the location and depth of the bite (bites to the head and body tend to be more severe than bites to the legs or paws); the age, size, and health of the dog; the time elapsed before treatment; and 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 USA. 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.

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