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Pit Viper Snake Venom Toxicosis in Dogs

Pit vipers are of the family Crotalinae, and are known by several species: Crotalus (rattlesnakes), Sistrurus (pigmy rattlesnakes and massassauga), and Agkistrodon (copperheads and cottonmouth water moccasins). These snakes have retractable fangs and can be distinguished by the heat-seeking pit located between the nostril and eye on their triangle-shaped heads. Their range is throughout the continental U.S. Bites most often occur in rural areas where these types of snakes are most frequent.

Toxicity of the venom is considered hematoxic, which means that it causes blood poisoning in the victim. Several species have subpopulations with lethal neurotoxic venoms, meaning that the venom attacks the nervous system (e.g., Mojave rattlesnake). The general ranking of severity is: (1) rattlesnakes, (2) moccasins, (3) copperheads.

The venom causes local tissue injury and interferes with coagulation of the blood. It also affects the cardiovascular and respiratory systems. Eighty-five percent of bite victims have altered laboratory values and clinically important swelling, with severely low blood pressure from the pooling of blood within the nervous system or pulmonary (lung) vessels. Fluid loss is secondary to severe swelling.

Symptoms and Types

In most dogs, there are puncture wounds on the head and forelimbs. In addition, symptoms may be delayed for 8 hours after bite, including:

• Local tissue swelling and pain surrounding bite site
• Bruising, with possible dead tissue and sloughing at bite site
• Red patches and spots on tissues and mucous membranes
• Rapid heart beat
• Shallow respiration
• Depression and lethargy
• Nausea
• Excessive salivation 
• Low blood pressure and shock

Causes

Victim-associated

• Bite site - bites to tongue and torso are of major concern
• Size of victim may affect severity of the reaction
• Elapsed time between bite and initiation of treatment will result in increased severity of symptoms
• Activity level of victim after the bite - activity increases absorption of venom in the system
• Owner may see bite marks, or heard the snake nearby at the time of injury (such as with rattlers)

Snake-associated

• Venom toxicity is higher in spring, lower in fall; highest in very young snakes.
• Aggressiveness and motivation of snake can increase venom value

Diagnosis

You will need to give a thorough history of your dog’s health, recent activities and onset of symptoms. Unless you saw the snake bite your pet, the diagnosis may be complicated by the fact that many other things can cause the same symptoms. For example, insect bite, blunt trauma, penetrating wound, animal bite, penetration of foreign body, or a draining abscess can bring about many of the same symptoms of snakebite. 

A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis. Your veterinarian will obtain important information from the blood test and urinalysis. Clotting tests can also indicate the origin of the symptoms, as clotting disorders are often a symptom of snakebite. Your doctor may also conduct an electrocardiogram to evaluate the functioning of your dog’s heart.