02/03/2025
Great info for all pet owners. Thanks, Doc! 🦨🦝
Welcome to Science Sunday!
Today’s topic is the canine rabies vaccine. In 1885, Louis Pasteur was presented with a 9-year-old boy who had been mauled by a rabid dog. The rabies vaccine had only been tested in dogs and rabbits at that time, but it was obvious that the boy would not survive without medical intervention. Every day for 10 days, the boy was given 12 doses of the vaccine. A month later, the boy had recovered. Unfortunately, this major breakthrough was too late for Edgar Allan Poe who died from rabies in 1849 which he contracted while feeding feral cats.
Rabies is responsible for tens of thousands of human deaths annually, with infections usually following a bite or scratch from a rabies-infected animal. According to the World Health Organization, rabies-infected dogs serve as the main source of human rabies transmission globally, contributing up to 99% of all rabies cases in humans, while in the Americas, bats are the most common source of human infections. In the U.S., the dog rabies variant, once endemic in small animals, has now been nearly eradicated. However, wildlife species, which carry their own rabies variants, present a constant danger of reintroduction of rabies to dogs. In 2024, there were 23 confirmed cases of rabies in Missouri with 22 of those cases found in bats and 1 in a cat. 8 of those cases were found in the St. Louis region.
While in vet school, I was presented with a litter of golden retriever puppies, along with the mom and dad, from a backyard breeder. They had not vaccinated any of the dogs. They were severely ill and near death. They had all attacked and killed a racoon in the yard 2-3 weeks previously. All dogs were humanely euthanized. Blood tests and analysis of their brains after euthanasia found that they were infected with both rabies and distemper.
Virtually all mammals are susceptible to rabies infection, including domestic animals (e.g., dogs, cats, cattle, horses) as well as wild mammalian reservoir populations (e.g., raccoons, skunks, foxes, bats). Regardless of the species affected, rabies causes acute, progressive encephalitis (inflammation of the brain) which is usually fatal.
All rabies vaccines administered in the U.S. and Canada are inactivated, or killed, meaning the virus has been processed so it can't cause disease. While most vaccines require two to four initial boosters, the rabies vaccine is a little different. Like other killed vaccines, the initial dose of a rabies vaccine triggers the immune system to be able to create antibodies that can fight rabies if the dog is ever exposed to the virus. The rabies vaccine is so effective that it's very rare for dogs who've been vaccinated to become infected.
Vaccine antibodies wane over time, causing the rabies vaccine to lose its efficacy. This is why dogs must get follow-up booster doses. Dogs usually receive one booster a year after their initial shot and then get it once every one to three years to maintain immunity. In most areas, keeping your dog up to date on their rabies vaccine is required by law.
Because vaccines work by stimulating the immune system, the side effects of rabies vaccine in dogs are usually due to a stimulated immune system. Side effects can include mild fever, mild loss of appetite and mild to moderate loss of energy for 24 to 36 hours after vaccination. It's also possible for dogs to experience soreness and mild swelling at the injection site. Occasionally, dogs develop a small, painless swelling at the injection site that can last for a couple of weeks. In rare cases, dogs may develop a small, circular area of hair loss at the site of injection.
Anaphylactic reaction can occur with the introduction of any substance into the body. Nuts, fish, milk, insect stings, penicillin and vaccines are a few substances that can cause allergic reactions that can progress to anaphylaxis. This usually occurs within a few seconds or minutes of exposure to allergic substances. This involves hives, swelling and sudden drop in the blood pressure and sometimes shock which can lead to death. I am allergic to aspirin and an accidental ingestion 15 years ago sent me to the emergency room. In my 22 years of being a veterinarian, I have never had a vaccine induced anaphylactic reaction in my practice. (Knock on wood.) I have heard of a few of my colleagues experiencing this in their practice, but it is usually a once-in-a-career event.
In the state of Missouri, a rabies vaccine may only be administered by a licensed veterinarian. The protocol at my practice is to give 1 rabies vaccine when a puppy, then give the vaccine every 3 years as an adult. A puppy must be at least 14 weeks old to receive a rabies vaccine. This is when the maternal antibodies that the puppy received from mom’s milk wane enough to not interfere with the vaccine so that the puppy can mount a meaningful immune response to the disease.
