Parvovirus can make for some sick puppies

Farm Forum

Buster was a walking definition of a “sick puppy.” Except that he wasn’t walking right now. Just a couple days ago, this 3-month-old Rottweiler was active and playful. Today he seemed all played out, stretched passively on the veterinarian’s exam table. He was weak and tired with sunken eyes. His owners reported that Buster had not wanted to eat or drink much water for the past day and a half. He had thrown up a few times and this morning he had cut loose with a wave of diarrhea.

The vet listened to the owner’s story while he examined the pup. His already strong diagnostic suspicions were confirmed when Buster had another diarrhea accident on the exam table. A vet’s sense of smell is a not-uncommonly-used diagnostic tool. And the smell from Buster’s accident registered “parvovirus” in the vet’s brain right away.

Most dog owners have probably heard of canine parvovirus. It’s a common and necessary component of “puppy shots”: vaccines administered to puppies to prime their immune systems against common canine diseases. Fortunately, this is where the familiarity with parvovirus ends for most dog owners, because the vaccine does a good job preventing illness.

But for others, parvovirus can be devastating and potentially fatal. Parvovirus shows up when puppies are incompletely vaccinated, or if vaccinated pups are unlucky enough to encounter so much virus it overwhelms their system.

In hindsight, Buster was at risk of parvovirus because he had missed his second puppy vaccination. Pups should be vaccinated for parvovirus beginning as early as 6 weeks of age. They should get boosters every 3-4 weeks after that until they’re at least 4 months old. These frequent boosters are necessary because the pup likely has antibodies against parvo from his mother. These are good because they protect the very young pup, but they can also neutralize a vaccine. We can’t predict which dose will “take,” so we repeat it until we are assured that the latest one will work.

This virus itself presents challenges. First, it is very contagious. It does not take many viruses to infect a susceptible pup. Secondly, it is very resistant in the environment. Many of the normal disinfectants we use don’t kill parvovirus. Unless special disinfectants are used, once it’s in a kennel or exam room, it can readily spread to other dogs.

Like most viruses, parvovirus has a preference for what type of body cell they like to infect. Parvo infects rapidly-dividing cells. The cells that line the intestine and cells in the bone marrow are prime targets because they’re always regenerating. As a result, the pup’s gut lining becomes raw and dysfunctional, resulting in a diarrhea that’s sometimes bloody and typically has a distinct stench to it. Rapid dehydration results from this loss of fluid through the intestine, and it’s worsened by vomiting.

Parvovirus’ effects on the bone marrow are just as bad. The virus destroys the cells that would normally form white blood cells – the body’s defense against infection. As if the gut problems aren’t bad enough, now the infected pup has very little immune system left to help him conquer the virus.

When parvo is diagnosed, all treatment stops are pulled out. Vets have to replace the pup’s lost body fluid through IV’s. They give antibiotics because the damaged gut is more likely to let bacteria into the bloodstream. And they have to somehow keep the pup’s nutrition up in the face of vomiting and a lackluster appetite. Significantly, all these efforts have to be done in isolation, with meticulous attention given to cleaning, disinfection, and biosecurity so that the clinic’s normal patients don’t become infected too.

All of these efforts are aimed at supporting the pup’s system while the gut cells regenerate and regain function. Sometimes they’re not successful. In the case of Buster, it took several days of IV fluids in isolation to keep him going through the course of his disease. He had a good outcome, but only after a long time and a hefty veterinary bill. If a new pup is going to join your household this year, make sure vaccination against parvovirus is at the top of your list.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at or at 605-688-5171.