Parvovirus
October, 1996
Canine parvovirus infection is a common disease and is
life-threatening to affected puppies. The virus probably first
appeared around 1976, possibly as a mutation from feline
distemper virus, but was not actually identified until 1978. It
is found worldwide, and is ineffective only to domestic dogs and
wild canids, such as coyotes, foxes and wolves. The virus poses
no threat to humans.
Parvovirus may be deposited in any environment, either by direct
contamination with the stool of an infected dog, or is spread by
being carried on objects, people or animals. It may remain
ineffective in the proper environment for months. Dogs become
infected by ingestion or inhalation of the virus. Once in the dog’s
body, it multiplies in the tonsils and lymph nodes and then
spreads through the bloodstream. It has its strongest affinity
for the small intestine, where it can cause severe disease by
attacking the intestinal lining.
Most infections in adult dogs cause little or no problems, but
puppies between 6 and 18 weeks old can be highly susceptible.
Signs usually starts 3 to 8 days after exposure and may include
severe bloody diarrhea, vomiting, poor appetite, lethargy and
fever. A number of complications can occur, such as
life-threatening endotoxic shock caused by intestinal bacteria
escaping into the bloodstream. Less common complications include
low blood sugar, anemia and secondary bacterial infections, such
as pneumonia. Rarely, young puppies will die suddenly from the
effects of the virus on heart muscle. Clinical signs are more
severe when other diseases are also present, such as parasitism
or canine distemper virus infection. Unfortunately, the virus may
be present in the stool of an infected dog before any of these
signs are seen, and most recovered puppies continue to shed
active virus in their stool for one to two weeks or more.
Due to the lack of an effective and available drug to kill the
virus, the most important aspect of treatment of infected dogs is
fluid administration, frequently intravenously, to prevent or
reverse life-threatening dehydration and loss of electrolytes.
Other accepted practices are the use of antibiotics, transfusions
and drugs that combat diarrhea, vomiting and endotoxemea. Despite
aggressive treatment, many puppies still die of this disease.
Younger age groups have higher mortality rates. Those that
survive the disease are expected to make a full recovery and have
long-term immunity.
Preventing infection can be achieved by decreasing the risk of
exposure to the virus and by a sound vaccination program. Likely
contaminated environments can be disinfected with chlorine
bleach. Dilute 1 ounce in 1 quart of water. Because the virus is
present in most outdoor areas, eliminating exposure can be almost
impossible, but puppies can be kept fairly restricted until their
vaccination series is complete. All pups are temporarily
protected by maternal antibodies they acquire through nursing.
The purpose of a vaccination is to stimulate the body into
producing its own, longer-lasting, antibodies. However, the
presence of maternal antibodies suppresses the body’s
response to vaccination. In addition, as levels of maternal
antibodies become too low to give protection, they may still
block the immune system’s response to vaccination. Levels of
maternal antibodies high enough to interfere with vaccination may
persist until the puppy is anywhere from 6 to 18 weeks old.
Therefore, even if a puppy is correctly vaccinated every 3 to 4
weeks from weaning until 4 months of age, there can still be a
period of a few weeks where it has inadequate protection and is
susceptible to infection. Despite this “window” of
susceptibility, routine vaccination has significantly decreased
the incidence of canine parvovirus infection and is strongly
recommended. However, because of the ubiquitous nature of the
virus and our inability to create a perfect vaccine, parvovirus
infection will likely remain a common disease for many years.