Reports of a shortage of rattlesnake vaccine for canines has some pet owners in the west concerned. Yet, while the makers of the vaccine fought to get the drug back on the market — finally receiving the license in late May — an industry association is taking the opportunity during the news cycle to ask veterinarians to warn clients there are no tests proving efficacy of the drug.

The American Animal Hospital Association (AAHA) reported creators of the vaccine were on a conditional license, which had a time limit. Since 2004, the vaccine was given renewals every two years as a limited market drug. While conditional licensure is intended to be temporary, there is no statutory limit on the number of times a conditional license may be renewed.

Pursuing licensure

Red Rock Biologics and Hygieia Biological Laboratories, the two companies that work together to create the vaccine, told a Sacramento, California. based media outlet they submitted more data for a full license in 2023, but the data was not immediately accepted by the USDA. The companies supply about 5,000 veterinary hospitals nationwide with the vaccine, the only national source for what is touted as a safe option for dog owners living in areas with high rates populations of rattlesnakes.

When the license was turned down, the creator of the vaccine and senior staff veterinarian at Red Rock Biologics, Dr. Dale Wallis, worked with Congressman Doug LaMalfa, R-Cal., and a long list of veterinarians to advocate for the renewal. The lobbying effort succeeded and on May 26, the USDA's Animal and Plant Health Inspection Service issued a renewal.

"Conditional licenses are issued when there is no commercial product available, but there is a need. The manufacturer has to show purity, safety, and a reasonable expectation of efficacy to get this kind of license. It’s issued for things like emergency conditions — like an outbreak of some sort — or, in our case, something called a limited market. This is where products are developed to address a problem, but the market is so small it doesn't warrant the cost of full licensure," Wallis said in a recent interview on Vet Watch.

This means future conditional licenses could, in theory, be denied as well but seemingly unlikely considering the vaccine has been approved for conditional licenses since 2003.

Many dog and horse owners, including those in the Big Horn Basin, vaccinate their pets in an effort to give them the time — touted by the makers of the vaccine — to get them to a veterinarian for treatment. However, despite the trust of the vaccine from many veterinarians, including locally, the lack of efficacy testing concerns regulators, industry insiders and pet owners.

One of the problems of proving efficacy is testing envenomated dogs in a controlled setting. Attempts, if any, have not been widely reported.

There have been tests on species of rodents, but due to the lack of testing specifically on dogs, the AAHA issued the following statement: “Veterinarians choosing to use this toxoid should be aware of the lack of peer-reviewed published data. Polyvalent antivenin therapy is an alternative to vaccination in suspect cases of rattlesnake bite.”

Association Task Force member Dr. George E. Moore, said the vaccine was included in the guidelines because it was commercially available, there was a market for it, and “for good or for bad,” the manufacturer continued to make it.  

“Some practitioners who use it and recommend it in dogs in high-risk areas with higher-risk lifestyles believe it to be beneficial,” he said, “Are they right? We really can’t prove it or disprove it.”

Here they come 

Rattlesnake season — the time period when the snakes are not in their brumation (the period in their dens during the cold seasons) start as early as March and can run as late as October and even November if the weather is unseasonably warm, according to the Asclepius Snakebite Foundation, a 501(c)3 non-profit organization dedicated to improving outcomes for snakebite victims through a combination of innovative research, clinical medicine, and education-based public health initiatives.

There are two species of rattlesnakes in Wyoming; the prairie rattlesnake is common in northwest Wyoming and the midget faded rattlesnake, which is endangered, can only be found in southern Wyoming. There are no rules concerning killing or possessing prairie rattlers, but it is illegal to kill or possess a faded midget rattler.

The American Kennel Club reports few snakebites on dogs prove fatal before you get to the emergency veterinarian, but it depends on the size of the dog, the type and size of the snake, if or how much venom was delivered and where on the dog the bite is located. It also advises if pet owners see adverse reactions, including anaphylaxis, in previously vaccinated then envenomated dogs, contact your veterinarian immediately.

"Call your veterinarian or local emergency veterinary clinic immediately, let them know your dog was bitten by a snake, and ask if they carry antivenom. It's better to drive to a clinic that’s further away if it means your dog will have access to antivenom. Antivenom works best when given immediately, but it is still effective hours, and even days, after a bite," the club said in its literature.