“Cowboy 4884” left a comment on an ancient (in Internet terms) post titled “Can Dogs Catch Parvo Twice?” (The post is a perennial favorite — it was one of my earlier posts, but it still draws page views and comments.)

I took four pitbull mix puppies into the veterinarian to get checked out. They were 12 weeks old. All received a clean bill of health. Seven days later, one started acting shy while in the pen. When I let them out to run around the house, they all had bundles of energy. None of the puppies were ever let outside.

I vaccinated all the puppies at 8 weeks with a 5-in-1, and again at 11 weeks with MAX PV. Someone called animal control and said that I was selling puppies. Animal control came out and said I had to take the puppies into a vet to get checked out. I don’t really trust vets here in California, but the puppies checked out fine.

I gave away three puppies prior to taking in the last four. I’ve contacted the new owners and the puppies are doing fine and the owners are very happy.

As of today, all the puppies have come down with parvo. Two were given away, and of those one has been put down and the two I have left are very sick. I feel that they caught or were infected with parvo at the veterinarian hospital.

Canine parvovirus (known colloquially as parvo) is the most dreaded disease of puppies. The virus attacks the intestines and bone marrow, leading to lethargy, weakness, loss of appetite, vomiting, diarrhea, and immune system compromise. Without treatment, the overwhelming majority of parvo-infected puppies die. With appropriate treatment, most survive.

Parvo is among the hardiest and most ubiquitous viruses known. It survives for years in the environment. It is ultra-infectious, and only a few organisms are enough to lead to infection. Infected dogs and puppies shed the virus by the millions. Parvo is everywhere.

Is it possible that the puppies caught parvo at the vet’s office? Sure. Vets take steps to keep their hospitals free from parvo (this usually involves using one of the few cleaning agents that can kill the virus), but there is no way to guarantee that any place will be parvo-free.

However, it is also possible that your home could have been contaminated by any previous dog that entered the house. You or a guest may have tracked the virus into the house on your shoes or clothing. Any person who sets foot outside has the potential to bring the virus indoors.

The question of where your dogs contracted parvo is less important than how they were able to contract the disease. There is no way to avoid contact with the virus. The only defense is vaccination. Properly vaccinated dogs (including puppies that are receiving their vaccines on schedule) very rarely become infected. And it is almost unthinkable that every dog in a litter would become sick if they were all vaccinated properly.

The issue here lies with the vaccines. The 5-in-1 vaccine that was given at 8 weeks and the MAX PV given at 11 weeks are both designed to be effective against parvo. They were given at the correct times. But they didn’t work.

One or both vaccines was either ineffective (it may have expired, or have been improperly stored, handled, or reconstituted; it also might have been counterfeit) or was administered improperly.

I recommend that you carefully investigate the source of any vaccines that you buy in the future. If you’re planning on introducing any dogs into your house, you’re going to need those vaccines. Your house is now contaminated with billions upon billions of viruses. Puppies will be at especially high risk. I recommend only adopting mature, fully vaccinated dogs.