Rattlesnakes live in a variety of habitats, ranging from wetlands, deserts and forests, and from sea level to mountain elevations. Rattlesnakes are most active in warmer seasons, from Spring to Autumn. In southern latitudes (and here in Southern California) they are occasionally found year-round. Dogs are at risk for rattlesnake bites; in fact dogs are about 20 times more likely to be bitten by venomous snakes than people and are about 25 times more likely to die if bitten. Snake bites are life threatening, extremely painful, expensive to treat, and can cause permanent damage even when the dogs survive. Dogs can encounter a rattlesnake anytime they are in rattlesnake habitat. You and your dog may live in rattlesnake habitat, or perhaps you travel through or frequently visit places where rattlesnakes are found. Maybe rattlesnakes are around when you take your dog hiking, camping or hunting. Like people, dogs may stumble over the location of a snake by accident. Curiosity or a protective instinct can place your dog at risk. When dogs encounter snakes during play or work in the snake’s natural habitat, most bites tend to occur on the face or extremities. The rattlesnake bite is generally “hemotoxic” which means that it exerts its toxin by disrupting the integrity of the blood vessels. The swelling is often dramatic with up to 1/3 of the total blood circulation being lost into the tissues in a matter of hours. The toxin further disrupts normal blood clotting mechanisms leading to uncontrolled bleeding. This kind of blood loss induces shock and finally death. Facial bites are often more lethal as the swelling may occlude the throat or impair ability to breathe. Less than a decade ago, a dog unfortunate enough to be bitten by a large Western Diamondback rattlesnake and injected with a full load of venom faced a grim fate, particularly if it was more than a couple of hours away from medical help. Since its availability in 2003, the Red Rock Biologics rattlesnake vaccine has helped provide the best protection against poisonous snakes and has become the standard of preventive veterinary care for dogs at high risk for rattlesnake bites.
The canine rattlesnake vaccine comprises venom components from Crotalus atrox (western diamondback). This vaccine is meant for use in healthy dogs to help decrease the severity of rattlesnake bites. The vaccine is produced from inactivated Crotalus atrox venom with an adjuvant and preservatives added. Dogs develop neutralizing antibody titers to C. atrox venom; the vaccine is specifically for the toxin of the Western Diamondback rattlesnake and provides the best protection against the venom of that particular rattlesnake, however the vaccine has been shown to provide cross protection against the venom of other types of rattlesnakes and copperheads since the venom of pit vipers share some of the same toxic components. In fact, most of the 15 species of rattlesnakes in the United States have fairly similar venom. This is how one antivenin is able to cross-protect against so many rattlesnake species. The protection afforded by the vaccine depends on the similarity of snake venoms to the Western Diamondback.
The vaccine however does not provide protection against the Mojave rattlesnake, Eastern Diamondback rattlesnake, cottonmouths or coral snakes.
The vaccine works by stimulating the dog’s immune system to produce antibodies against rattlesnake toxin. Initially, a dog should receive two subcutaneous doses about 30 days apart. It is best to give vaccination boosters about 30 days before beginning of exposure to rattlesnakes. Protection peaks about 30 to 45 days after boosters and lasts about six months. As the antibodies are short lived and the vaccine typically only provides protection for six months, a booster shot is necessary either once a year one month before “snake season” or twice a year in areas where rattlesnakes are year-round risks. The protection level that a dog receives from the vaccine depends upon how well that individual dog produces these specific antibodies and may vary. Protective antibodies made by your dog in response to the vaccine start neutralizing venom immediately. On average, antibody levels in recently vaccinated dogs are comparable to treatment with three vials of antivenin. Almost no vaccine is effective 100% of the time. There are undoubtedly some dogs whose immune systems just won’t produce as many antibodies necessary for maximum protection but the partial protection they receive may still be enough to save their lives or help them recover more quickly. Therefore, this vaccine should not be used solely as a means of protection against rattlesnake bites. It is meant to provide some protection and to reduce the severity of the snakebite. Adverse events are reported in far less than one percent of all vaccinated dogs. Most of these side effects are mild and need no veterinary care. The most common side effect is the development of an injection site cellulitis; these vaccine site reactions can be treated with hot, moist compresses, antibiotics, and pain relief medication if necessary. Systemic reactions (typically flu like symptoms) are reported in fewer than one in 3,000 vaccinates and usually self-resolve in two to three days.
Even good antibody protection can be overcome in special snakebite circumstances. A vaccinated dog’s resistance to rattlesnake venom can be overcome with enough venom or special circumstances. But what are those circumstances? Special snakebite circumstances include smaller dogs, larger snakes, multiple snake bites to the same dog, and bites near vital organs. Smaller dogs are always going to have a harder time fighting off the same amount of venom as larger dogs. Larger snakes can produce and deliver larger doses of venom in a single bite. Multiple snake bites to the same dog can naturally deliver larger quantities of venom. Bites near vital organs allow the venom to start destroying those organs before the antibodies in the dog’s blood plasma have time to find and neutralize the harmful proteins in the rattlesnake venom. Other special circumstances may include some dogs whose immune systems just don’t produce enough antibodies, intravenous bites, and some snake species that the vaccine has little or no protection against.
The reported benefits of vaccination include a delay in onset of symptoms, fewer symptoms, less severe symptoms, a decrease in mortality rate, faster recovery times, and little or no tissue necrosis. In addition, most veterinarians also report less painful dogs, less lethargy, less swelling, that the swelling progression typically reversed within the first 1 to 2 hours, and that dogs had full recoveries in about 24 to 48 hours. As mentioned previously, according to Red Rock Biologics, the manufacturers of the rattlesnake vaccine, the antibody levels in recently vaccinated dogs are comparable to treatment with three vials of antivenin. So, although canines still need emergency veterinary treatment, they should experience less pain and a reduced risk of permanent injury from the rattlesnake bite. Snakebites are always an emergency. Even if your dog is vaccinated against rattlesnake venom, always get the pet to a veterinarian as soon as possible following any snakebite. Even non-venomous snake bites can lead to serious infections and antibiotic treatment may be needed. A veterinarian can determine what additional treatment is needed.
Since the most common mechanism of death from rattlesnake bite is circulatory collapse, intravenous fluid support, antibiotic therapy, cardiac and blood pressure monitoring, antihistamine administration and pain management are very important. Fluids may be started at a relatively slow rate if the patient is stable but should signs of impending trouble occur, circulatory volume replacement and treatment for shock is indicated. Blood transfusion may be necessary if life-threatening blood loss has occurred. A minimum of twenty four hours of post-bite observation and hospitalization is prudent. In addition, treatment of snakebite should include antivenin administration. There are numerous misconceptions about antivenin. The first is simply the name of the product. It is not “anti-venom.” It is not a single injection that provides the antidote to snake bite venom. Antivenin is a biological product consisting of antibodies made in response to exposure to four common Crotaline venoms. The antibody serum is reconstituted into an intravenous drip that is run into the patient over at least 30 minutes or so. Antivenin is expensive (at least $600-$800 per vial) and a large dog with a severe bite is likely to require several vials. Antivenin is very helpful in the inactivation of snake venom but there is a narrow window during which it must be used. After about 4 hours post-bite, antivenin is less effective in countering the effects of snake venom.
In summary, rattlesnake envenomation is a serious life threatening injury and immediate veterinary care is warranted for the best success rates in surviving the ordeal. The benefits of prophylactic vaccination include more time to get to a veterinary hospital, the reduction in the amount of pain and swelling experienced, faster recovery times, and a decrease in the mortality rate. It is not meant as a sole means of protection. Emergency treatment consisting of intravenous fluid support, antibiotic administration, antihistamines, pain management and antivenin will result in the best chance of successfully surviving a rattlesnake bite.
The Animal Medical Center of Southern California is devoted to providing the best medical, surgicalm and emergency critical care available in veterinary medicine. As important as our medical expertise is, we believe that excellent care combines state-of-the-art veterinary medicine and surgery with a focus on compassion and respect for your pet and for your family.
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