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
disease.
What are
the symptoms of parvovirus
infection?
There 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
breeds.
The most common form of the
disease is the intestinal form
known as
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
presence of
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
CBC and
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 treatment.
Intravenous
administration of a balanced
electrolyte solution
is preferred, but in less severe
cases,
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 the
titer 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,
immunization 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
immunized.
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 the disease.
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.
Conclusion
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 the
disease.
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.
