Snake Bites and the Rattlesnake Vaccine

The weather is getting warmer, which means snakes are on the move! While most snakes are nonvenomous, there are two families of poisonous snakes, the Elapidae and the Crotalidae, that populate the United States. Coral snakes belong to Elapidae and make up only 1% of all venomous snakebites to dogs and cats. By far, the majority of all venomous snake bites in the United States are caused by members of Crotalidae, better known as pit vipers.

Pit vipers have triangular-shaped heads, heat-sensing “pits” between their nostrils and eyes, and retractable front fangs. Rattlesnakes, copperheads, and water moccasins are all pit vipers. Rattlesnakes are responsible for the majority of deaths in both human and animal victims. Copperheads are the most common snake to cause bites, due to their tendency to live close to human habitation. Water moccasins can be aggressive and have a higher tendency to deliver venom when they bite.
Ninety percent of venomous snakebites occur from April to October. It was once thought that snake venom became more toxic during the hotter months; however, this has been disproved. Snakes do become more aggressive in the hotter months and are, therefore, more likely to deliver a larger amount of venom. Pit vipers can control the amount of venom that is injected during a bite. An initial defensive strike is usually lacking in venom. The more threatening the situation, the more venom the snake injects into the bite. If a snake is in pain, it typically delivers the entire venom load.

The severity of a snake bite depends on multiple factors. First, the severity of a snake bite is directly related to the amount of venom injected during the bite. Secondly, different snakes carry a different potency of venom. In general, the toxicity of pit vipers decreases from rattlesnakes, to water moccasins, and then to copperheads. Location of the bite on the animal is also a factor, as it may affect the rate of absorption of the venom. In general, smaller animals are at more risk than larger ones. Finally, medications that an animal may be taking can also influence the severity. For example, a dog taking aspirin may be more prone to bleeding.

Snake venom can cause a number of clinical signs. The most common is extreme swelling and pain at the bite location. Usually, two puncture wounds are visible at the site of the swelling. The venom contains enzymes that are destructive to tissue, so the skin and muscle will usually slough off. Sometimes, the animal will vomit or go into shock. Severe cases can cause bleeding disorders, so signs of hemorrhage may be evident on the gums or elsewhere.

If your animal receives a snake bite, there is little first aid that you can administer at home. Several “at home” treatments, such as cutting open the wound, applying hot/cold packs, or sucking out the venom can actually cause more harm than good. Seek veterinary attention right away. The main objective is to try to keep your pet as calm as possible, because the more excited they get, the faster the venom is spread. Try to keep the bite wound below the heart during transport to your veterinarian. Your veterinarian may advise you to give Benadryl, mainly to try to keep your pet calm. Aggressive IV fluids are recommended to help prevent shock. An antivenin is also available at specialty hospitals, which helps reverse many of the effects of snake venom. It is unfortunately rather expensive, but it does diminish symptoms. Not all snake bites require the antivenin, but you do not know how bad the bite will be until hours after it happens. The antivenin must be administered soon after the bite to be most effective.

A rattlesnake vaccine is available to help lessen the severity of bite wounds and has been in production since 2004. It is most effective against the Western Diamondback Rattlesnake (which is the most common rattlesnake here in Kerr County), but it also cross-protects against other rattlesnakes (excluding the Mojave). The vaccine also gives protection against Copperheads. It is not effective against water moccasins or coral snakes. While it is difficult to formulate a study on just how effective the vaccine is (due to the various factors that influence the severity of a snake bite), experience suggests that vaccinated dogs typically have less severe reactions to the snake bites and tend to recover more quickly. Even if a dog receives the vaccine, it is still essential that they receive veterinary treatment! The vaccine is most effective 4-6 weeks post vaccination, and this protectiveness slowly declines after that. On average, good protection lasts about 6 months after vaccination, so we recommend that dogs ideally be vaccinated in the spring. As with any vaccine, there is always a risk of the rare allergic reaction. More commonly, we will sometimes see a lump that persists in the area where the vaccine was given that usually resolves with time. The rattlesnake vaccine is not part of our core vaccination program, but we do recommend it for hunting dogs or dogs with a high exposure to snakes. If you feel that your dog is at risk for coming into contact with a rattler or a copperhead, ask us about the vaccine!

By: Ryan Roberts, DVM

Peterson, Michael E. & Talcott, Patricia A. Small Animal Toxicology, 2nd Edition. “Snakebite: North American Pit Vipers”, pp 1017-1037. St Louis, MO, 2006.