Every year rattlesnakes bite more than 100,000 dogs in the United States, with an estimated 40% of bites resulting in severe reactions and fatal reactions in about 5% of bites. So why wouldn’t every owner in areas where rattlesnakes are common vaccinate their dogs against rattlesnake venom? In brief, because there isn’t any solid proof that the rattlesnake vaccine for dogs works as intended. There are no studies that demonstrate an increased survival rate or a reduced rate of severe reactions among vaccinated dogs.
RATTLESNAKE BITE DANGERS FOR DOGS
Rattlesnake venom causes severe swelling at the bite location (often on the face or paws), bleeding, a dangerous drop in blood pressure, shock, and eventual breathing paralysis. In addition, the venom contains components that can break down proteins, cell membranes, intercellular matrix and/or connective tissue, resulting in painful tissue damage at the site of the bite.
Veterinary clinics in high-risk areas carry antivenin (also known as antivenom), which helps neutralize the venom.
To make rattlesnake antivenin, either sheep or horses (depending on the manufacturer) are injected with small amounts of venom from a number of rattlesnake species. The immune systems of the sheep or horses respond by producing protective immunoglobulins that neutralize the specific toxic antigens in the snakes’ venom. Blood is collected from the animals and the hemoglobin is separated from the plasma; the plasma fraction containing the protective immunoglobulin is used to make the antivenin.
Antivenin is expensive – it costs $450 or more per vial – and sometimes, several vials are needed to counteract the bite’s venom. Dogs who are bitten by rattlesnakes are most likely to survive if they receive prompt treatment, which may include antivenin, fluids, antibiotics, anti-inflammatories, antihistamines, hospitalization, and/or surgery.
RATTLESNAKE VACCINE FOR DOGS
Twenty years ago, Red Rock Biologics developed Crotalus Atrox Toxoid (CAT), a rattlesnake bite vaccine for dogs and horses. The inactivated venom used in its production came from western diamondback rattlesnakes; vaccination with CAT elicits production of immunoglobulins capable of binding to and neutralizing the major protein fractions of Crotalus atrox (western diamondback) venom.
The vaccine is labeled only “for protection against the venom of the western diamondback rattlesnake.” However, according to Red Rock Biologics, canine antibodies that develop in response to this vaccine may also recognize and bind proteins in other North American rattlesnake venoms.
The CAT vaccine is given in two doses, administered four weeks apart. It’s recommended to give an additional booster four weeks after the second vaccination for dogs who weigh more than 100 lbs. The vaccine can be given as early as 16 weeks of age, needs to be repeated annually, and should be given a month before snake season begins, as it takes the dog’s body about four weeks to produce peak levels of the antibodies needed for protection.
The vaccine does not offer immunity from the effects of a snake bite. Instead, says the manufacturer, because the dog’s antibodies have been available to neutralize venom components from shortly after the bite, far less tissue destruction should occur than in an unvaccinated animal, and better outcomes are expected.
How effective is the rattlesnake vaccine? That’s the key question. No clinical trials have proved that this vaccine actually works, and a peer-reviewed study published in 2014 found that it did not protect dogs requiring treatment with antivenin (“Effects of the canine rattlesnake vaccine in moderate to severe cases of canine crotalid envenomation,” Veterinary Medicine, October 2014). That study, which examined records of 82 Southern California dogs treated for naturally occurring rattlesnake bites, concluded, “No statistically significant difference in morbidity or mortality between vaccinated and unvaccinated dogs was found. The findings of this study did not identify a significantly protective effect of previous vaccination in the cases of moderate to severe rattlesnake envenomation that require treatment with antivenin.”
OPINIONS ON THE RATTLESNAKE VACCINE VARY, EVEN AMONG VETERINARIANS
Because of the vaccine’s questionable efficacy, and the fact that vaccinated and unvaccinated dogs must receive the same medical care when bitten by a snake, many veterinary hospitals, such as the University of California Davis Veterinary Medical Teaching Hospital, do not recommend it for their canine patients.
Some veterinarians, however, believe that the vaccine might delay the venom’s effect so that the owner can reach a veterinarian in time to save the dog’s life or decrease the venom’s effects. For this reason, they recommend the vaccine for dogs at high risk in areas where immediate treatment is impossible.
“I’m a big believer in the rattlesnake bite vaccine,” says Lorrie Boldrick, DVM, in Orange, California (barefootveterinarian.com). “Any rattlesnake bite is a medical emergency, but the description that stays with me is that the whole point of the vaccine is to give you extra time, to make it more likely that you’ll be able to get to a veterinarian with a live dog.”
Dr. Boldrick explains that it’s impossible to know how severe a bite is when it happens, because a rattlesnake may release no venom at all when it bites (this is called a dry bite), a moderate, or a maximum amount. Rattlesnakes are able to control the release of venom; they use as much as they need to kill their prey. The amount they use when they bite a dog is highly variable. Because of this, every bite needs to be treated as promptly as possible.
At least six of Dr. Boldrick’s vaccinated patients have been bitten by rattlesnakes and all of them survived. “I believe that each of them received at least some venom,” she says, “and two of them got a lot, and they did fine. I know of so many vaccinated dogs who recovered with minimal care that I’m convinced the vaccine helped by reducing the venom’s effect and providing extra time to seek treatment.”
The vaccination is not expensive – about $30 to $40 for each vaccination at most veterinary clinics – but it’s not entirely benign, either. An estimated 5% of vaccinated dogs develop a reaction at the injection site, ranging from sensitivity to an abscess that requires veterinary treatment.
TO VAX OR NOT TO VAX?
We recommend making an appointment with your veterinarian to discuss the CAT vaccine and your dog’s relative risk from the bite of a venomous snake. It’s not proven whether this vaccination can stimulate antibodies quickly enough to protect your dog from the venom in a snakebite, or whether the vaccination would offer protection from whatever species of rattlesnake your dog encountered. Keep in mind that your vet may have a bias for or against the vaccine, based on her experience in your area.
And, vaccine aside, consider that there are proven benefits to strengthening your dog’s response to your recall and “leave it” or “walk away” cues. If these behaviors are not reliable, keep your dog on a short leash, and keep your eyes wide open when you are walking with your dog in rattlesnake habitats.