RATTLESNAKE VACCINATION

I have received so many e-mails and calls from all of you that I've pulled this from next month's newsletter and am posting it here.

Many of you may be receiving a note from your vet stating that your dog is due for vaccinations. It may also state that it’s time for a “rattlesnake vaccination.” If you’re like most owners, you’re scratching your head because you’ve never heard of this one before. Here is what I’ve come up with, in its simplest form, after numerous phone calls and review of scientific articles regarding this vaccine.

This vaccine (Crotalus Atrox Toxoid) was developed by a company called Red Rock Biologics in about 2000. It is specifically developed for the Western diamondback rattlesnake. This company prior to and since this vaccine has developed no other vaccinations of any type. (Take that as you will).

The Western diamondback rattlesnake (Crotalidae atrox/ C. atrox) is a viper and one of 15 viper varieties in the United States. Because of its size and aggressiveness it is the most dangerous of the vipers. Its range is Arkansas, Texas, Oklahoma, New Mexico, Arizona, Southern California, Southern Nevada and the Hidalgo area of Mexico. For those of us living outside these states this snake is of no, or very little, concern.

Each year in the United States about 300,000 domestic animals are bitten by venomous snakes and 99% of the bites are from the pit viper species (Crotalidae) which include rattlesnakes, cottonmouths and copperheads.

Rattlesnake venom is NOT all the same as it is made of various proteins containing toxins to nerves (neurotoxins) or blood cells (hemotoxins.) While quantity of toxin is related to the size of the snake (larger snakes/larger volume), the potency varies depending on species, age, area, time of year and nutritional status. A younger snake may inject less volume, but it may contain more neurotoxin elements. Also, a snake may miss the target and have premature venom release. Between 20-30% of all human and animal bites are “dry bites”, meaning no venom is released. Most animals receive their bites on the face or front leg(s). (I can attest to this as a cat of mine was bitten on the leg by a viper and lived.)

Rattlesnake antivenins used for many years has been an equine-based whole antibody preparation sold under the name of Antivenom (Crotalidae) Polyvalent (Wyeth) which often resulted in a high risk (56%) of hypersensitivity reactions and delayed serum sickness reactions. The Wyeth (human) and Fort Dodge (animal) products are both available, but both may create an immune reaction in dogs and, therefore, skin testing before administering is strongly suggested and may be helpful, but not always accurate.

Recently CroFab (Protheris), a sheep-derived preparation, has become widely used in place of the equine-based product for humans as it has been shown to have less immune reaction. But, Fort Dodge, remains the only product labeled for use in dogs and is much cheaper ($100-$200 per vial) as compared to Ovine FAB ($600-$700 per vial).

The rattlesnake vaccine calls for 2 to 3 doses depending on the size of the dog, each 3 to 6 weeks apart with an annual booster in spring. Additional doses may be needed at 4 to 6 months in high-risk dogs, such as those that field trial, work livestock in the desert areas, etc.

The vaccine, with a 1% injection site reaction, seems to be safe. However, site reaction numbers seem to fall into the 1 in 150 dog range and the reactions range from mild irritation at injection site to severe abscess the size of softballs with deep-tissue pus. Because dogs’ response to this vaccine is varied, a bitten animal MUST be considered a veterinary emergency due to the fact that the amount of venom may overwhelm the titers in the vaccine, not all species of snakes are well covered by this vaccination and it doesn’t address any secondary tissue necrosis or infection. Your dog will, in all probability, still require antitoxin treatment and the vaccine has shown no significant difference in the course of treatment if your dog is bitten.

University of California/Davis will not, at this time, advocate the vaccine’s use because of its “questionable efficacy, cost, and no substantial difference in acute therapy if bitten…” They do, however, note that in high-risk dogs from areas where treatment may be “substantially delayed, the rattlesnake vaccine may buy time for the owner to get their animal to a veterinarian and may potentially decrease the overall severity of envenomation.” The UCD Veterinary Medicine Teaching Hospital official stance: “Based on existing evidence, the UC Davis VMTH does not currently recommend routine vaccination of dogs for rattlesnake envenomation, and the vaccine is not stocked by our pharmacy.”

Each of you must make the decision as to vaccinating or not. I, personally, from all I’ve read, the fact we are not in the diamondback range and my discussions with friends in the lab at UCD VMTH will not have my dogs vaccinated for this particular problem.