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Canine parvovirus (CPV) disease is currently the most common
infectious disorder of dogs in the United States.
'Parvo' is a highly contagious disease characterized by diarrhea
that is often bloody. Prior to 1980, most canine parvovirus that
caused disease was Type 2 (CPV-2). After 1980, CPV-2 was replaced by
CPV-2a became more common and in 1986, another variation called
CPV-2b appeared. In the past few years, a new strain, CPV-2c has
been detected. Today, CPV-2b has largely replaced the previous
strains as the most common parvovirus causing disease in the dog.
There is currently some discussion that there may be other strains
that are beginning to emerge and have yet to be formally identified.
Current vaccinations have helped to control the spread of this
disease but despite being vaccinated, some dogs still contract and
die from parvo. There is much that we do not know about the virus or
the best way to control the disease, but we are learning new
information daily. Misinformation about the disease, its spread, and
vaccination is widespread. We hope that with a better understanding
of the disease, pet owners will be able to make good health
decisions for their dogs that will help prevent and reduce the
spread of this disease.
How is parvovirus spread?
Parvovirus is spread through contact with feces containing the
virus. The virus is known to survive on inanimate objects - such as
clothing, food pans, and cage floors - for 5 months and longer in
the right conditions. Insects and rodents may also serve as vectors
playing an important role in the transmission of the disease. This
means any fecal material or vomit needs to be removed with a
detergent before the bleach solution is used. The bleach solution
should be used on bedding, dishes, kennel floors and other
impervious materials that may be contaminated.
The normal incubation period (time from exposure to the virus to
the time when signs of disease appear) is from 7-14 days. Virus can
be found in the feces several days before clinical signs of disease
appear, and may last for one to two weeks after the onset of the
What are the symptoms of parvovirus
is a broad range in the severity of symptoms shown by dogs that are
infected with parvovirus. Many adult dogs exposed to the virus show
very few, if any, symptoms. The majority of cases of disease are
seen in dogs less than 6 months of age with the most severe cases
seen in puppies younger than 12 weeks of age. There are also
significant differences in response to parvovirus infections and
vaccines among different breeds of dogs, with Rottweilers, Doberman
Pinschers, and Labrador Retrievers being more susceptible than other
The most common form of the disease is the intestinal form known
enteritis. Parvovirus enteritis is characterized by
vomiting (often severe), diarrhea, dehydration, dark or bloody
feces, and in severe cases, fever and lowered
white blood cell counts.
Acute parvovirus enteritis can be seen in dogs of any
breed, sex, or age. The disease will progress very rapidly and death
can occur as early as two days after the onset of the disease. The
gram negative bacteria, parasites, or other viruses can
worsen the severity of the disease and slow recovery.
A less common form of the disease causes myocarditis
(inflammation of the heart).
How is parvovirus infection diagnosed?
Not all cases of bloody diarrhea with or without vomiting are
caused by parvovirus and many sick puppies are misdiagnosed as
having 'parvo.' The only way to know if a dog has parvovirus is
through a positive diagnostic test. In addition to the more time
consuming and expensive traditional testing of the blood for
titers, a simpler test of the feces with an enzyme-linked
immunosorbent assay antigen test (ELISA), commonly called the CITE
test, is also available through most veterinary clinics. Testing of
all suspect cases of parvo is the only way to correctly diagnose and
treat this disease. A complete physical exam and additional
laboratory tests such as a
chemistry panel help to determine the severity of the disease.
How is parvovirus disease treated?
The treatment of parvovirus is fairly straightforward and
directed at supportive therapy. Replacing fluids lost through
vomiting and diarrhea is probably the single most important
Intravenous administration of a balanced
electrolyte solution is preferred, but in less severe
subcutaneous or oral fluids may be used. In severe cases,
blood transfusions may be necessary. Antibiotic therapy is usually
given to help control secondary bacterial infections. In those dogs
who have severe symptoms, antiserum against endotoxins may be given.
Corticosteroids may be given if the animal is in shock. In cases of
severe vomiting, drugs to slow the vomiting may also be used. After
the intestinal symptoms begin to subside, a broad spectrum
de-worming agent is often used. Restricting the food during periods
of vomiting is also necessary and parenternal nutrition (providing
nutrients intravenously) may be necessary.
Undertaking the treatment of affected dogs and puppies without
professional veterinary care is very difficult. Even with the best
available care, the mortality of severely infected animals is high.
Without the correct amount of properly balanced intravenous fluids,
the chance of recovery in a severely stricken animal is very small.
All parvoviruses are extremely stable and are resistant to
adverse environmental influences such as low pH and high heat.
Exposure to ultraviolet light and sodium hypochlorite (a 1:32
dilution of household bleach - ½ cup bleach to 1 gallon of water)
can inactivate parvovirus. The bleach solution can be impaired by
organic matter and needs to have adequate exposure time and proper
concentrations to work effectively.
Immunity and vaccination
If a puppy recovers from parvovirus infection, he is immune to
reinfection for probably at least twenty months and possibly for
life. In addition, after recovery the virus is not shed in the
feces. There are many commercially prepared
attenuated (modified) live CPV-2 vaccines available. The
current vaccines protect against all strains of the canine
parvovirus, including the relatively new parvovirus-2c strain.
Although some people have expressed concern about the possibility of
modified live vaccines reverting to a virulent strain after being
given and then causing disease, studies have repeatedly shown that
this does not occur. Commercially prepared vaccines are safe and do
not cause disease.
The primary cause of failure of canine parvovirus vaccines is an
interfering level of maternal antibody against the canine
parvovirus. Maternal antibodies are the antibodies present in the
mother's milk during the first 24 hours after the puppy's birth. The
age at which puppies can effectively be immunized is proportional to
of the mother and the effectiveness of transfer of
maternal antibody within those first 24 hours. High levels of
maternal antibodies present in the puppies' bloodstream will block
the effectiveness of a vaccine. When the maternal antibodies drop to
a low enough level in the puppy,
by a commercial vaccine will work. The
complicating factor is that there is a period of time from several
days to several weeks in which the maternal antibodies are too low
to provide protection against the disease, but too high to allow the
vaccine to work. This period is called the window of susceptibility.
This is the time when despite being vaccinated, a puppy can still
contract parvovirus. The length and timing of the window of
susceptibility is different in every puppy in every litter.
In one study of a cross section of different puppies the age at
which they were able to respond to a vaccine and develop protection
covered a wide period of time. At six weeks of age, 25% of the
puppies could be immunized. At 9 weeks of age, 40% of the puppies
were able to respond to the vaccine. The number increased to 60% by
16 weeks, and by 18 weeks of age, 95% of the puppies could be
When we examine all of the information about maternal derived
antibodies, windows of susceptibility, breed susceptibilities, the
possibility of unidentified strains, and the effectiveness of
different vaccines, we begin to see why there are so many different
vaccination protocols and why some vaccinated animals still develop
Vaccination protocols have been developed that will help protect
the widest range of dogs. In using these protocols, we understand we
will be vaccinating some dogs that are not capable of responding and
we will be revaccinating some dogs that have already responded and
developed a high titer. But without doing an individual test on each
puppy, it is impossible to determine where the puppy is in its
immune status. We also realize due to the window of susceptibility,
some litters will contract parvovirus despite being vaccinated. By
using quality vaccines and an aggressive vaccination protocol, we
can make this window of susceptibility as small as possible. The
generally recommended protocol is to vaccinate puppies against
parvovirus beginning at 6-8 weeks of age, and revaccinating every 3
weeks until the puppy is 16-20 weeks of age. A booster is given at
one year of age and every 1-3 years thereafter.
In summary, parvovirus is a very common problem that is a huge
killer of puppies. Due to its ability to be transmitted through
hands, clothes, and most likely rodents and insects, it is virtually
impossible to have a kennel that will not eventually be exposed to
Modified live vaccines are safe and effective, but
despite the best vaccination protocol, all puppies will have a
window of susceptibility of at least several days where they will be
at risk. In addition, the newer CPV-2c strain presents new
challenges since it is less detectable in laboratory tests and
current vaccines may not be as effective in providing protection
against it. Prompt treatment by a veterinarian will increase
survivability in infected puppies and working with your veterinarian
on a vaccination program that is best for your puppy is important.