Vaccinations: Canine Parvovirus Infection


Our ‘Paws to Protect’ topic this month is vaccinations. Every time you have your pet vaccinated against a disease, you are taking a proactive step in protecting your pet. In order for pets to be fully protected against a disease, there are some important things owners will need to understand. By now, you likely realize that vaccines help prevent illness and the spread of disease. In this week’s blog, we will utilize the canine parvovirus infection (parvo) to discuss and illustrate some of the nuances of vaccines that you may not be as familiar with.

Consider an owner who has just adopted an 8-week-old puppy. Nothing is known about this puppy’s history prior to adoption. The owner brings the puppy to the clinic for a new puppy exam. The puppy checks out as a normal, healthy puppy. At the end of the visit, the puppy is dewormed, vaccinated with a combination distemper / parvovirus / adenovirus / parainfluenza vaccine, and sent home with it’s preventive medications (heartworm, intestinal parasite, flea/tick). The owner is instructed to bring the puppy back in 3 to 4 weeks for the next puppy visit and more vaccinations. At first, the puppy does well at home. However, after about 5 days, he starts vomiting, develops diarrhea, and is extremely lethargic. He is taken to the clinic and examined again. The puppy is weak and dehydrated. A parvo test that screens for parvovirus in the feces is positive. Labwork reveals some changes consistent with parvo (including a low white blood cell count). Based on all these findings, the puppy is diagnosed with parvo. Given the severity of the situation, the puppy is hospitalized so that he can be treated with aggressive supportive care.

Parvo is a highly contagious viral disease in dogs. Often, it affects puppies because their immune systems are not fully developed. Symptoms of parvo can include vomiting, diarrhea (with or without blood), fever, weakness, and inappetence. The illness can cause the animal to become severely dehydrated, and septicemia (bacteria in the blood) and even death can result. The virus is transmitted through the feces of infected dogs, and it is incredibly stable in the environment. Since this is a viral infection, treatment is largely symptomatic and supportive. Ultimately, the puppy in our example does great and makes a full recovery.

Considering the highly contagious nature of parvo alongside the severity of clinical signs and potential to cause death, it is easy to understand why vaccinating against parvo is so important. If we can prevent this from even happening in the first place, that’s so much better than having to deal with the effects of the virus in the animal.

Going back to our scenario, one might start to wonder why this puppy developed parvo since it received a parvo vaccine. In this scenario, there are actually a few different reasons that could have contributed to this puppy developing parvo:

  • Since it can take 6 to 10 days for a dog to develop signs after being exposed to parvo, this puppy was probably exposed to parvo before the new owner adopted the puppy (so it was likely exposed prior to the vaccine).
  • The parvovirus vaccine is a type of vaccine that needs to be boostered 2 to 4 weeks after the initial vaccine. Since this puppy only received 1 vaccine, it was not fully protected.
  • In puppies, we have another contributing factor found in their immune system. Puppies receive maternal antibodies from their mother. These maternal antibodies can actually work against the parvo vaccine we administer, making it less effective. We know that maternal antibodies dwindle around 16 weeks of age. This is a major reason puppies need to have the parvo vaccine boostered every 2 to 4 weeks until they reach 16 weeks of age (when we know maternal antibodies are not interfering with our vaccines any further).

Vaccinations are a fantastic way to protect our pets from many diseases. However, from our example, we see that we also have to remember to keep things in context. Sometimes extra steps will need to be taken to minimize risk. For all diseases that we vaccinate against, the immune system needs about 2 weeks to develop a good response to the vaccine. If a booster vaccine is needed, the pet won’t be fully protected until 2 weeks after the booster. And for puppies (and kittens), maternal antibodies can interfere with some vaccines up until about the age of 16 weeks.

Do you have questions about your pet’s vaccination status or needs? Visit our ‘Paws to Protect: Vaccinations’ section or give our office a call today!

Author: Dr. C. Noureddine, DVM, MS, MS