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Summary
Pit vipers (family Crotalidae) are common snakes in the US. Their bites are responsible for 99% of the 300,000 estimated venomous snake bites sustained by domestic animals every year. Pit vipers include rattlesnakes, copperheads and cottonmouths. Rattlesnakes are reportedly the most common biters among these.
In the US, dogs tend to encounter rattlesnakes most commonly between April and October, when the warmer weather makes their exposure a more likely occurrence. Dogs will be bitten either after accidentally encountering a snake in the brush or after spying them and attacking (because they sense a threat or as a result of a strong predatory drive).
Symptoms and Identification
The venom these snakes inject into their victims is a strong neurotoxin (nerve toxin) and hemotoxin (blood cell toxin). Different kinds of rattlesnakes carry different types and strengths of venom and some may inject no venom at all.
Acute swelling, one or two puncture wounds, bleeding and pain at the site (limping or flinching when the area is touched) are the most common signs that a dog has been bitten. The face and extremities are the most typical sites.
The hemotoxin in the venom will destroy blood cells and skin tissue and will result in severe localized tissue swelling and possibly even internal bleeding. Severe reactions to the hemotoxin include severe swelling tissue necrosis (purpling and blackening of the surrounding tissue), and a drop in blood pressure.
Dogs who receive more of the neurotoxin in the venom tend to experience more life-threatening reactions, including rapid paralysis that may affect the respiratory muscles.
The severity of the reactions tend to be dependent on the dose a dog receives. In fact, in about 20% to 30% of cases, dogs will receive "dry" bites and the resulting signs are relegated to the possibility of a skin infection at the bite site. However, a reported 5% of dogs die as a result of rattlesnake bites.
History of contact with a rattlesnake and clear signs of a bite -- either because of the telltale wounds or characteristic tissue damage -- are how most dogs are diagnosed with the possibility of rattlesnake envenomation.
Affected Breeds
Any breed of dog is susceptible to the effects of rattlesnake venom. Some dogs, however, are more likely to have a high drive to attack these animals. Dogs with high prey drives and rural or hunting lifestyles are more likely to find themselves in harm's way when it comes to rattlesnake envenomation.
Treatment
Treatment of rattlesnake envenomation depends upon the amount and type of venom the animal has been exposed to. In general, however, the faster an animal is seen by a veterinarian, the greater the chance of survival and the fewer complications they'll experience.
Treatment tends to focus on the following steps:
Step #1: Prevent or delay absorption of venom. Cleaning and flushing of the wound is imperative. However, infiltrating the bite area with saline may contribute to its dispersal so cleansing is best achieved only superficially. Sucking the venom out is no longer recommended.
Step #2: Veterinarians will neutralize any absorbed venom by injecting antivenin. Poison control centers will provide antivenin availability information in the event rattlesnake envenomation is uncommon in your area.
Step #3: Supporting respiration and counteracting the effects of the toxin and maintaining cardiovascular function is crucial. Intravenous fluids are critical here. Corticosteroids may help lessen tissue destruction but their implementation is considered controversial. Broad-spectrum antibiotics, however, are always recommended. Pain relievers, too, play an important role in an animal's overall comfort and help raise the probability of survival in severe cases.
More intensive care options may be necessary. Blood transfusions and even ventilator care may be indicated in some cases.
Veterinary Cost
The cost of treatment for rattlesnake envenomation depends greatly on the amount and type of venom the animal has been exposed to as well as on the length of time it takes to receive veterinary help (delaying veterinary assistance increases the number of expensive complications).
Care for rattlesnake envenomation can be very inexpensive for animal who have received "dry" bites. These dogs can be helped for the cost of bite treatment and antibiotic therapy (often under $100 or $200).
If severe, life-threatening complications ensue, however, dogs may require intensive care in a specialty setting. In the event this is necessary, or should tissue damage be so extensive that follow-up surgeries are required, expenses may run into the many thousands for treatment of one single rattlesnake bite.
Prevention
Preventing exposure to rattlesnakes is the best approach in all cases. Here are some tips experts recommend owners follow:
Avoid hiking with dogs during peak times of the year (April through October).
Stay away from areas with tall grass, rocks or wood piles.
Stay on trails and keep dogs leashed at all times.
Keep pets away from rattlesnakes if they're encountered as they can strike up to a distance one-half of their length.
Using a walking stick to rustle bushes along trail helps alert snakes of your presence and keeps them away.
Around your house, remove all food sources (such as rodents) and minimize hiding places (such as wood piles).
Given the rural, active lifestyles of some dogs, however, this may not be realistic. In those cases, a vaccine may be a reasonable alternative for dogs who encounter these snakes on a regular basis, especially if they tend to be far away from veterinary care.
Unfortunately, there's only scant evidence to support the efficacy of this vaccine. Nonetheless, it's considered relatively safe and affordable and may be helpful for some dogs. Vaccinated or not, dogs who are bitten by snakes should be seen by a veterinarian as soon as possible!
References
Clark R, Selden B, Furbee B: The incidence of wound infection following crotalid envenomation. J Emerg Med 1993; 11: 583-586.
Kerrigan K, Mertz B, Nelson S, et al: Antibiotic prophylaxis for pit viper envenomation: prospective controlled trial. World J Surg 1997; 21: 369-372.
Malasit P, Warrell D, Chanthavanich P: Prediction, prevention, and mechanism of early (anaphylactic) antivenom reactions in victims of snakebites. Br Med J 1986; 292: 17-20.
McNalley J, Dart R, O'Brien P: Southwestern rattlesnake envenomation database (abstract). Vet Hum Toxicol 1987; 29: 486.
Peterson M, Meerdink G: Venomous bites and stings. In Kirk R (ed): Current Veterinary Therapy X. Philadelphia, WB Saunders, 1989, pp. 177-186.
Russell F, Ruzic N, Gonzales H: Effectiveness of antivenin (crotalidae) polyvalent following injection of crotalus venom. Toxicon 1973; 11: 461-464.
Snyder C, Knowles J, Pickens J, et al: Snakebite poisoning. In Catcott E (ed): Canine Medicine. Santa Barbara, American Veterinary Publications, 1968, p. 256.
Stewart M, Greenland S, Hoffman J: First-aid treatment of poisonous snakebite: Are currently recommended procedures justified? Ann Emerg Med 1981; 10: 331-335.