One of the funny things about living in Southern California is knowing that some people won’t go hiking because they are terrified of rattlesnakes. They think as soon as they step foot onto a trail, a horde of vicious, fanged menaces are going to leap out and inject them with poison. Maybe this helps keeps the crowds limited on our beautiful outdoor spaces (except in Torrey Pines on Labor Day, my goodness!). I’m sure the same people avoid the ocean because of sharks too. However unlikely an encounter may be, some people, including our beloved Dr. Tedder, are terrified of any and all snakes, and especially ones with built-in maracas. Fear is always an effective marketing tool, and there are a number of silly “snake-proofing” products on the internet. They run the gamut from ridiculous to plausible, and one of the more interesting products available is a rattlesnake vaccine (http://www.redrockbiologics.com/) for dogs and horses. But is this vaccine a good idea? The science isn’t there to support it just yet, although it’s better than some other stuff out there. Read on pet lover, and we will hopefully shake out fact from fiction.
While encounters are rare, I have to concede that we will occasionally come across a venomous little tube of muscle undulating across the trail. It’s exciting and scary and the best option is always to be respectful and keep your distance, which makes a bite VERY unlikely. But while we bipeds may be careful and cautious, often we’re hiking with dogs who can only be described as “simple-minded”. Their eagerness to make new friends and grab things that look like sticks can certainly get them into trouble. It’s estimated that there may be more than 100,000 venomous snakebites in dogs and cats in the US each year1. Fortunately deaths are pretty rare, but treatment is almost always necessary.
If a dog is bitten by a rattlesnake, they need veterinary attention ASAP, no question. If the dose of venom is high enough, then the dog will need antivenom, which is the antidote to rattlesnake venom. Antivenom is essentially pre-made antibodies to a mixture of different rattlesnake venoms4 (more on that later, but yeah they’re not all the same type of toxins). We can inject these antibodies into the bitten patient and they soak up all of the venom, stopping it from causing harm. It tends to work really well, although multiple doses are often needed and it’s not cheap (get pet insurance!). Also, if there are any delays in treatment, the antivenom may not be enough to prevent permanent damage. Obviously the best case is to not get bit in the first place (we recommend rattlesnake avoidance training), but as we all know, sometimes stuff happens.
Which finally gets us to this rattlesnake vaccine. Is it a good idea to have your pet “immunized” against snake venom? Sounds cool, right, and the idea behind it is interesting. Here’s the concept: create antivenom in the bloodstream so that when the snake bites the dog, the antidote is already there and the venom automatically gets neutralized. This is actually exactly how antivenom works when we give it. When a snake puts venom in a dog (bad), a veterinarian can inject antivenom (good) to stop the venom from doing bad things. So wouldn’t it be great to just have the antivenom in there in the first place?
Maybe a little Old West analogy will help. Let’s say there’s a bad guy in town, and we don’t know when he’s gonna show up and get to causin’ trouble (please continue to read in a Sam Elliot voice). The town is the body, and the bad guy is the venom. Think of a vaccine as a way for us to tell the body to target that bad guy before he gets there, like a “Wanted” poster that gets everybody in town on alert. In theory, the antibodies (townspeople) will jump on the venom as soon as it hits the body. If there’s enough of them, they’ll rangle him up and lock him in jail, and nobody gets hurt (ok you can stop the fun voice if you want to).
Like I said, it’s a very interesting theory, and in fact some squirrel species are naturally resistant to rattlesnake venom2 (how cool is that!). So we can basically make your dog immune to the venom, right?
Here’s the big problem with the vaccine: we don’t know if it works. Kind of a tough sell, right? We know that it could, maybe, possibly, under-the-right-circumstances, work. But there are actually quite a few leaps of faith to we’d need to make to trust it. To stretch our Old West analogy further, let’s consider what we know about this vaccine. We know that the vaccine does post wanted posters (i.e. it makes the immune system create antibodies) and we know that it riles the townspeople up and that they do react when they see the bad guy (i.e. the antibodies react with and neutralize the venom). This all sounds good until we dig a little deeper and ask a few important questions. Here’s when we should be double thinking that leap. Ready for some monkey wrenches in the plan?
- What if it’s not the right bad guy who’s causing a ruckus?
There are about 40 different species of rattlesnake species (we have four species in our county5) and the vaccine only produces neutralizing antibodies to one of them for sure. It might have some effect on other venoms, but we really don’t have any idea. Are you a good enough herpetologist to know which snake bit your pet?
- How long do those “Wanted” posters stay up for?
If they get taken down after a week of not seeing our villain, how riled up are the townspeople gonna be? As of right now we have no idea, meaning, we have no idea how long a dog might actually benefit from this vaccine and when to give boosters.
- How many bad guys are gonna show up?
If it’s just one troublemaker, the small town posse could probably handle him. But what if there’s a whole gang of them? We often don’t know how much venom is injected, and we don’t know how many antibodies are produced, so if our math is off by even a little bit, the antibodies can be overwhelmed.
Could it work? Yeah. However, there are some “buts”, and those are big “buts”. I would not trust it to save my dog’s life. Even if a dog had been given this vaccine, that pet owner would need to react exactly the same way if their dog does get bitten, which means they need to get them a veterinarian with antivenom right away. In a recent study3, dogs that had been vaccinated did no better than dogs who hadn’t been vaccinated. If you really want a pet that’s immune to rattlesnake venom, adopt a ground squirrel, or learn this move (don’t do either of those please).
Written (and external links inserted) by:
Greg Bishop, DVM
References:
- Armentano RA, Schaer M. Overview and controversies in the medical management of pit viper envenomation in the dog. Journal of Veterinary Emergency and Critical Care. 2011 Oct 1;21(5):461-70.
- Biardi JE, Chien DC, Coss RG. California ground squirrel (Spermophilus beecheyi) defenses against rattlesnake venom digestive and hemostatic toxins. Journal of chemical ecology. 2005 Nov 1;31(11):2501-18.
- Cates CC, Valore EV, Couto MA, Lawson GW, McCabe JG. Comparison of the protective effect of a commercially available western diamondback rattlesnake toxoid vaccine for dogs against envenomation of mice with western diamondback rattlesnake (Crotalus atrox), northern Pacific rattlesnake (Crotalus oreganus oreganus), and southern Pacific rattlesnake (Crotalus oreganus helleri) venom. American journal of veterinary research. 2015 Mar;76(3):272-9.
- https://www.crofab.com/Treatment-With-CroFab/Production
- http://www.sdnhm.org/science/herpetology/resources/faqs-on-rattlesnakes/
Hi Dr. Bishop,
I just read your post: “Rattlesnake vaccines. Are they effective?” I would like to point out a problem with one of your statements. In your article you referred to a paper that stated: “In a recent study #3, dogs that had been vaccinated did no better than dogs who hadn’t been vaccinated.”
You referenced publication “#3” which was my paper (I’m JG McCabe, co-author). Our publication was a mouse study (double blinded study from UCLA) and not a dog study. I think you were referring to this paper by McGee, et al., which you did not reference in your article, (see reference and abstract below):
“Effects of the canine rattlesnake vaccine in moderate to severe cases of canine crotalid envenomation”; McGee J Leonard,1 Catherine Bresee,2 Andrew Cruikshank1
Veterinary Medicine: Research and Reports; Dovepress: 31 October 2014 Volume 2014:5; Pages 153—158
1Animal Specialty and Emergency Center, Los Angeles, CA, USA; 2The Biostatistics and Bioinformatics Research Center, Cedars-Sinai Medical Center, Los Angeles, CA, USA
Abstract: This is a retrospective multicenter study (2006–2012) examining a population of dogs with moderate to severe crotalid envenomation for protective effects of the canine rattlesnake vaccine. Five nonacademic emergency and referral veterinary hospitals in Southern California were involved in the study and contributed records regarding a total of 82 client-owned dogs that were treated for naturally occurring rattlesnake envenomation. All dogs received antivenin (Crotalidae) polyvalent, with dosages ranging from one to three vials (mean: 1.3±0.6). Fourteen dogs (17%) had a history of prior vaccination against crotalid venom. In univariate logistic regression modeling, cases with lower body weight (P=0.0001) or higher snakebite severity scores (P<0.0001) were associated with greater morbidity. 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.”
I would like to point out some major flaws with McGee’s publication and hopefully provide some insight on our study. I will start with the McGee publication. The dog records which were evaluated in this study were obtained from several clinics in the San Fernando Valley (SFV)and the only native rattlesnake in the area is the Southern Pacific Rattlesnake, (C.o.helleri or C. helleri…depending on if you’re a lumper or a splitter). McGee states that the most prevalent rattlesnake species in the area is the Western Diamondback (C. atrox). The closest Western Diamondback rattlesnake is ~ 100 miles away from the SFV and they don’t occur in Los Angeles County at all. Her conclusion that the vaccine is useless is based on the INCORRECT assumption that a vaccine made with Western Diamondback (C. atrox) venom and has no therapeutic value against a direct challenge by the same species (Western Diamondback bite). Unfortunately McGee did not do her research on the local rattlesnakes. What is actually happening is that the vaccinated dogs probably produced antibodies but they were non-specific antibodies that did not bind with the components of the Southern Pacific Rattlesnake (C. helleri )venom.
Our paper came to the same conclusion as McGee, but based on a different set of facts! I agree With McGee’s conclusion that the Red Rock vaccine does not provide cross protection from the bite of the only species of rattlesnake that occurs in the SFV (the Southern Pacific Rattlesnake, C. helleri). Our study showed that vaccinated mice, challenged with 2X-LD50 of C. atrox venom, had a 60% survival rate at 48 hours. Vaccinated mice, challenged with 2X-LD50 of C. helleri venom, had a 0% survival rate at 48 hours. The reason is because the venom composition between these two species is very different and so the antibodies produced by the vaccinated mice don’t recognize and bind with the individual components of the C. helleri venom. It should be noted that the vaccination did improve the survival time in all three groups which the manufactures (Red Rock Biologics) claims. The claim that it provides cross protection against most North American rattlesnake species (including the Southern Pacific Rattlesnake) is false. The currently available antivenom provides cross protection against all species of North American pit viper because it is made from the venom of 4 different species of pit viper. The current canine rattlesnake vaccine is made from the venom of one species and as expected provides little or no cross protection against the bite from a different species. I would only use the Red Rock vaccine on my dog if I lived in an area where the Western Diamondback rattlesnake was the most commonly encountered species of venomous snake. A new vaccine is needed that provides true cross protection. Our research shows that the current vaccine has very limited value in the state of California, but the concept of using a toxoid vaccine is sound!
Thanks for your time, James G. McCabe
Hello James, thanks for your comments! Thanks also for catching my error. I was in fact referencing a different paper than the McGee one, which I updated in the attached version of the blog post:
https://www.ncbi.nlm.nih.gov/pubmed/26341419
Since this study took place in the Phoenix area, and my brief, non-strenuous herpetological googleing tells me that C. atrox is found in the area, does that support the lack of evidence for the vaccine? I am not at all a snake expert, and I completely agree with your assessment about the McGee study, assuming the species are in fact that different.
I also completely agree that your guys’ study does show some of the vaccine’s potential, and I agree with your point about cross protection. My bigger concern was about proven efficacy in the field, even under ideal conditions. In addition to cross protection, we need to know about duration of immunity and safety. I just came across this case report about possible anaphylaxis due to previous crotalid vaccination:
https://www.sciencedirect.com/science/article/pii/S004101011730404X
I don’t think we can say conclusively that the vaccine sensitized these dogs but it does seem like a plausible risk. It would be really cool if the rattlesnake vaccine gets worked out. Thanks again for your input!