Some conditions that we see in the veterinary clinic tend to be seasonal – allergies, for example. While spring ushers in litters of adorable puppies and kittens, often it also brings with it outbreaks of a dreaded disease called parvovirus.
Parvovirus infects rapidly dividing cells, like those found in the lymphatic system, the gastrointestinal tract and bone marrow. The virus is also very hardy in the outside world and can be difficult to eradicate. It is easily carried on the shoes and clothing of those who have been exposed and can survive freezing temperatures on the ground over the winter.
To make matters worse:
- The virus is shed in massive amounts by infected dogs for two weeks just after exposure;
- Only a small amount of virus is needed to infect a dog; and
- The virus has been around since the 1970s.
All of these things mean that parvovirus is virtually everywhere in the environment, and puppies with weaker immune systems are at risk for infection. Initially, puppies (like humans) get their immunity from maternal antibodies they ingest while nursing. These antibodies protect the puppy from infections, but they start to wear off around four months of age. Luckily, puppies can also be protected from viruses by vaccines. Puppies get multiple rounds of the same vaccines because remaining maternal antibodies interfere with the vaccines. By giving a series of vaccines, vets are more likely to catch a puppy’s immune system when it is just running out of maternal antibodies and is ready to start making its own.
Puppies become infected with parvovirus orally – they ingest the virus from somewhere in their environment. Initially, the virus starts by looking for rapidly dividing cells, and finds that the lymph nodes in the throat are a good target. From there, the virus replicates until it enters the bloodstream and travels to the cells of the gastrointestinal tract and bone marrow.
Once in the bone marrow, the virus kills the cells of the immune system, effectively knocking out the puppy’s only defense to kill the virus.
In the gastrointestinal system, it destroys intestinal cells, rendering the intestines unable to absorb nutrients and causing severe diarrhea, vomiting and nausea. The barrier that separates digestive bacteria from the bloodstream is destroyed, allowing bacteria to enter the bloodstream, leading to septicemia (blood infection).
Parvovirus is fatal in one of two ways: severe diarrhea and vomiting leads to shock and death, or overwhelming infection in the bloodstream leads to septic shock and death.
Treatment consists largely of supportive therapy while the puppy’s immune system recovers enough to fight the virus on its own. Managing the symptoms is all we can do – that means giving intravenous fluids and antibiotics to combat dehydration and secondary infection, and trying to keep the puppy from feeling too nauseous. Puppies with parvovirus will need lengthy hospital stays to recover from their illness, and these can get quite costly. Without treatment, however, many puppies will succumb to the illness.
Parvovirus is especially frustrating for veterinarians, as it can almost always be prevented by vaccine. If you have a young puppy, make sure to ask your vet about vaccinating against parvovirus.