Parvovirus in Dogs

Parvovirus infection, commonly called “parvo,” is a disease of
dogs that affects the intestinal tract and causes vomiting,
diarrhea, fever, and decreased ability to fight infections. It
is especially severe in puppies. Doberman pinschers and
rottweilers are more susceptible and have more severe signs of
parvo than other breeds, but puppies of any breed or mixed breed
puppies can die from this disease.

Parvo is a relatively new disease entity in dogs that was first
identified in the late 1970s. The virus did not exist before
that time. It is believed that this is a disease caused by a
virus of the cat or other species that adapted itself to dogs.
When the virus first emerged, dogs of all ages became infected.
Now that the disease is in its second decade, usually only young
dogs are infected. This is because the virus is so contagious
and so commonly found in the environment that most older dogs
have become immune through vaccination or infection early in
life.

Oral intake of virus-infected materials transmits the infection
to susceptible dogs. Parvovirus multiplies in the intestinal
tract of infected dogs, and a billion virus particles per
teaspoon of stool can be passed during an infection. The virus
is sturdy and persists in the environment for at least 6 months.
It is impossible to eliminate the virus from contaminated soil
without killing all vegetation. For inside facilities, thorough
washing and rinsing followed by careful application of a
chlorine bleach solution containing 1 ounce of bleach per quart
of water is needed. Avoid skin and eye contact with the bleach
solution.

Infection of puppies usually results from exposure to
contaminated soil, and signs of disease are seen from 4 to 14
days after exposure. The initial signs are depression, loss of
appetite, and fever. Vomiting and blood-streaked diarrhea
develop within 1 or 2 days. These signs progress quickly to
dehydration and death in severely affected dogs. Puppies 6 to 8
weeks of age have a higher death rate than older dogs. The age
of onset of infection depends on exposure to the virus as well
as the pups’ level of antibodies against parvovirus.

Bitches that are immune by vaccination or previous exposure to
the virus pass some of their antibodies to their puppies in
milk. Depending on the amount of antibodies passed to the
puppies, the antibodies protect them for a few weeks to as long
as 3 months. The puppies’ bodies gradually degrade or break down
the antibodies and the puppies must then produce their own
immunity to be protected.

The initial damage to the body in parvo occurs because the virus
destroys the cells in which it reproduces. Unfortunately, there
is no antiviral treatment at this time. Treatment of dogs
infected with parvo depends on the severity of the infection.
Dogs with mild infections can recover with nursing care, but
those with severe infection become severely dehydrated. These
dogs require intravenous fluid to maintain their hydration
because they are unable to take in fluids and are losing large
amounts of fluid in the vomiting and diarrhea.

In addition to the fluid loss, the virus destroys the lining
cells of the intestinal tract, which allows bacteria from the
intestine to enter the body. When this bacterial invasion occurs
(septicemia), antibiotics must be given to kill the bacteria in
the bloodstream. In addition to allowing bacterial entry into
the bloodstream, the parvovirus damages the bone marrow, where
white blood cells are produced. Neutrophils, a specific type of
white blood cell necessary for destroying invading bacteria, are
severely reduced in numbers. Immune dysfunction causes some dogs
with parvo to die in spite of extensive treatment with fluid and
antibiotics.

The best approach to parvo is prevention of disease with
vaccination. Puppies should be started on vaccines at 6 weeks of
age and exposure to infected environments should be minimized
until the vaccination series is complete. Puppies should be
vaccinated every 2 to 3 weeks until 16 weeks of age. The long
course of vaccination is necessary because of the maternal
antibodies passed from the mother to the pups. Although these
antibodies protect against infection, they also interfere with
an effective response to vaccination.

Low levels of maternal antibodies interfere with vaccination but
may not protect puppies from infection. Advances in parvovirus
vaccines have resulted in improved vaccines that provide
effective protection despite some maternal antibodies. It is
advised that the exposure of puppies be minimized until vaccines
given at 16 weeks of age have been administered.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.