Canine Parvovirus Then And Now
When my best friend, Tom, I were junior students at Auburn University’s College of Veterinary Medicine, his dog became very ill. She stopped eating, began vomiting and had a horrible bloody diarrhea. Her doctors treated her the best they could with IV fluid therapy, antiemetics for the vomiting, and antidiarrheals. She had two blood transfusions to replace the red blood cells she lost to the intestinal bleeding. We couldn’t imagine that she could possibly live through it.
She did, though. Most likely because she was one of the older pets to be stricken with the disease, though few, if any, dogs had immune system protection from it.
Parvovirus. “Parvo.” That was 1979 and it didn’t have a name then, although parvoviruses were known to exist, as well as to cause disease in other species, most notably cats and pigs.
A year later, shortly after we graduated, the canine “parvo” epidemic swept the country. People lived in fear for their pets’ lives. Many would not venture inside a veterinarian’s facility for fear of exposing their pets to the disease. You may think I’m exaggerating, but I’m not. We were administering the closest thing we had to a vaccine for the disease, Feline Panleukopenia vaccine, because it is caused by a parvovirus and was believed to be the original virus from which canine parvovirus mutated. One day in Columbus, GA, I personally gave 800 vaccines to 800 dogs, and I worked in a 3-man practice then! People would come to the door, sans pet, and beg us to come to the car to vaccinate their animal. Mostly we acquiesced, but with that kind of volume it really threw a wrench in logistics.
Canine parvovirus kills the most rapidly-dividing cells in the body. That means intestinal lining, bone marrow stem cells and, in the youngest puppies, heart muscle. Often, even today, if a puppy dies suddenly with no clinical signs, the attack of parvovirus on the myocardium can be so quickly fatal that diarrhea and vomiting are never even seen.
More commonly, though, parvovirus victims present lethargic, with pale gums, anorexia, vomiting and bloody diarrhea. The atrocious odor associated with the diarrhea is mostly from the intestinal tract’s effect on the extreme hemorrhage, although some practitioners claim to be able to smell a difference between parvo diarrhea and other bloody diarrheas.
In the 80s the mortality rate for parvo cases was extremely high. Now it is much lower, and that relates to a combination of factors.
The biggest is communal immunity. When a large part of the population is vaccinated against a disease there is a spillover effect to unvaccinated members through association. Plus, it is difficult to get massive number of virus particles into a population unless a substantial portion of the population can become infected. With so many dogs well-vaccinated against parvovirus today, a widespread epidemic is almost impossible.
Virus mutation is a factor, also. There are two new strains of canine parvovirus since the 80s and neither has the virulence of older versions. On the other hand, virus mutation can go the other way. If the virus mutates to cause more serious disease, fatalities could increase.
Treatment has changed little since the disease first reared its ugly head. We still focus on treating the symptoms of vomiting, diarrhea and dehydration. Just as with the common cold, little can be done to combat the virus itself, so we do what we can. That means:
- Fluid therapy to offset the massive loss through the “stripped” intestinal tract. Today we have greatly-improved sources of colloids, which help to balance protein loss when serum flows out from the bleeding intestines.
- Blood transfusion to replace red blood cells, clotting factors and white blood cells.
- Antiemetics to control vomiting. Today’s injectable vomiting-control medications, especially Cerenia by Pfizer, far exceed the capabilities of older choices.
- Hyperimmune serum is now commercially available to help the weakened immune system of parvovirus patients fight off the attack.
- Human antivirals are used by some practitioners, while others argue that their availability is already short during flu season and thus should be reserved for the human population.
Three decades ago parvovirus was a death sentence for much of the young dog population. Today, parvo is a completely preventible disease, with vaccine failures being almost unheard of. Treatment is successful in the vast majority of cases, although it can easily cost one thousand or more dollars for the most aggressive therapy.
Like most diseases, parvovirus is more easily and less-expensively prevented than treated.
See you tomorrow, Dr. Randolph.