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Parvovirus-canine
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This is the actual canine parvovirus.
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CANINE PARVOVIRUS: WHAT IS IT?
Parvoviruses are a large group; almost every mammal species (including
humans) seems to have its own parvovirus. Fortunately, each virus is pretty
specific about what animals it can infect (i.e. the pig parvovirus will not
infect people, the canine parvovirus will not infect cats etc.) The canine
parvovirus will affect most members of the dog family (wolves, coyotes,
foxes etc.)
Parvoviruses are smaller than most viruses and consist of a protein coat
(a "capsid") and a single strand of DNA inside. It is hard to believe that
such a simply constructed organism could be so deadly; however, this virus
has proved especially effective at infecting rapidly dividing host cells
such as intestinal cells, bone marrow cells, cells of the lymph system, and
fetal cells. Parvoviruses are not enveloped in fat the way many other
viruses are. This makes parvoviruses especially hardly in the environment
and difficult to disinfect away.
While the parvoviruses of other species have been well known for decades,
the canine parvovirus is a relative newcomer. The original canine
parvovirus, discovered in 1967 and called "CPV-1," did not represent
much of a medical threat except to newborn puppies but by 1978, a new
variant, "CPV-2" appeared in the U.S. This newer version seems to
represent a mutation from the feline parvovirus (which is more commonly
known as the "feline distemper virus"). Because this virus was (and is) shed
in gigantic numbers by infected animals and because this virus is especially
hardy in the environment, worldwide distribution of the virus rapidly
occurred. At this time, the virus is considered to be "ubiquitous,"
meaning that it is present in EVERY ENVIRONMENT unless regular disinfection
is applied.
Attempting to shield a puppy from exposure is completely futile.
In 1978, no dog had any sort of immunity against this virus. There was no
resistance and the epidemic that resulted was disastrous. To make matters
worse, a second mutation creating CPV-2a had occurred by 1979, which
seemed to be even more aggressive. Vaccine was at a premium and many
veterinarians had to make do with feline distemper vaccine as it was the
closest related vaccine available while the manufacturers struggled to
supply the nation with true parvo vaccines.
Nearly twenty years have passed since then. The current form of the virus
is called CPV-2b . Virtually all dogs can be considered to have been
exposed to it at least to some extent which means that most adult dogs, even
those inadequately vaccinated can be considered to have at least some
immunity.
Parvoviral infection has become a disease almost exclusively of
puppies and adolescent dogs.
Parvoviral infection must be considered as a possible diagnosis in any
young dog with vomiting and/or diarrhea. With proper hospitalization,
survival rates approach 80%. Still, there are many myths and
misunderstandings about this virus, how it is spread, and how to prevent it.
The purpose of this web site is to clear up these misconceptions and provide
the public with an accurate information source.
Because the canine parvovirus is not enveloped in
fat the way the distemper virus is, canine parvovirus is especially
hardy in the environment. It is readily carried on shoes or clothing to
new areas (which accounts for its rapid worldwide spread shortly after
its original appearance). It is able to overwinter freezing temperatures
in the ground outdoors plus many household disinfectants are not capable
of killing it indoors.
Given that this is such a tough virus to destroy, many people want to
know exactly what they must do to disinfect an area that has contained
an infected dog or how long they must wait before safely introducing a
new dog to a previously contaminated area.
Here is what we know about how contaminated an environment is likely
to be:
- Infected dogs shed virus (in their stool) in gigantic amounts
during the 2 weeks following exposure. Because such enormous amounts
of virus are shed, there is a HUGE potential for environmental
contamination when a infected dog has been there.
- It is important to realize that because the canine parvovirus is
so hardy in the environment, it is considered "ubiquitous." This means
that NO ENVIRONMENT is free from this virus unless it is regularly
disinfected.
A parvoviral infection can be picked up ANYWHERE though it is easier
to pick up an infection in an area where an infected dog has been
present simply because of the larger amounts of virus present in a
contaminated area.
- Whether an individual dog gets infected or not depends on the
number of viral particles the dog experiences, what kind of immune
experience the dog has had with the virus before (vaccinated?
previously infected? how much past exposure?), and how strong the
individual dog is (stress factors, diet etc.)
A typical/average infectious dose for an unvaccinated dog is 1000
viral particles. For some dogs far less is needed. For other dogs, far
more is needed. An infected dog sheds 35 million viral particles (35,000
TIMES the typical infectious dose) per OUNCE of stool.
Indoor decontamination:
- Indoors, virus loses its infectivity within one month; therefore,
it should be safe to introduce a new puppy indoors one month after the
active infection has ended.
Outdoor decontamination:
- Freezing is completely protective to the virus. If the outdoors is
contaminated and is frozen, one must wait for it to thaw out before
safely introducing a new puppy.
- Shaded areas should be considered contaminated for seven months.
- Areas with good sunlight exposure should be considered
contaminated for five months.
Of course, the above presupposes that no decontamination steps (other
than waiting) have been taken. In most households, owners want to know
how to disinfect their homes to create a safer environment for the other
dogs there or to create a safe environment for a new or replacement
puppy.
Here's what we know about disinfection:
- Despite the introduction of new cleaners with all sorts of claims,
parvovirus remains virtually impossible to completely remove from an
environment. The goal of decontamination is to reduce the number of
viral particles to an acceptable level.
- The best and most effective disinfectant against viruses
(including parvoviruses) is BLEACH. One part bleach is mixed with 30
parts water and is applied to bowls, floors, surfaces, toys, bedding,
and anything contaminated that is colorfast or for which color changes
are not important.
Bleach completely kills parvovirus
- Disinfection becomes problematic for non-bleachable surfaces such
as carpet or lawn. Outdoors, if good drainage is available, thorough
watering down of the area may dilute any virus present. Since carpet
is indoors, it may be best to simply wait a good month or so for the
virus to die off before allowing any puppies access to the area.
Whether or not infection happens depends on the interaction of
three things: Host Vitality (including immune experience/vaccination
status), Virulence of the Virus (including how many viral particles
the host is exposed to), and Environmental factors. Obviously these
three aspects interplay somewhat (a stressful environment will
reduce host vitality, a dry environment will reduce the number of
viral particles etc.)
WHERE DOES VIRUS COME FROM?
Remember that this virus has been around for nearly 20 years, is
very hard to disinfect away, and is shed in large numbers by
infected dogs. This means that there is virus everywhere: on every
carpet, on every floor, in every yard and park. Virus is shed for
the first two weeks or less after infection in the stool of an
infected dog but only a tiny portion of infected stool (which could
be months old depending on the environmental temperature and
humidity) is needed to infect a non-immune dog. Some dogs become
what is called "subclinically infected" which means they do
not appear particularly sick. These animals tend not to be confined
since no one knows they are infected thus they can spread virus
around a large area depending on where they leave their droppings.
WHY ONLY PUPPIES?
The most important factors in parvovirus infection seem to be the
immune experience the host (dog) has had with the virus plus the
number of viral particles the host is exposed to. Twenty years ago
when the virus was new, all dogs young and old were susceptible but
now, because the virus is present everywhere, all dogs, even the
unvaccinated ones, have at least some immunological experience with
this virus. Any exposure no matter how small is likely to generate
some antibodies. Also, vaccination is a widespread process nowadays
and it is likely that a dog has had at least one vaccine at some
point. Will these antibodies be enough for protection? In general,
the answer seems to be yes as infection in dogs over age one is
somewhat unusual. It is important to realize, however, that this
observation should not be taken to mean that adult dogs should not
continue their vaccinations. Even though infection is somewhat
unusual in adult dogs, adult dogs should still continue their
vaccinations as this is a life threatening disease for which
treatment is expensive and no chances should be taken.
NATURAL PROTECTION?
When puppies are born, they are completely unable to make antibodies
against any infectious invader. They would be totally unprotected
except that nature has created a system to protect them. Their
mother secretes a special milk for the first day or two after giving
birth. This milk is called "colostrum." It contains all the
antibodies that the mother dog has circulating in her own body and
in this way, she gives her own immune experience to her off-spring.
These antibodies protect the puppies until they wear off sometime in
the first 4 months of life.
How much colostrum an individual puppy gets depends on its birth
order and how strong a nurser it is; not all puppies get the same
amount of antibodies. Every nine days the antibody levels possessed
by the puppies drops by half. When the antibody level drops to a
certain level, they no longer have enough antibody to protect them
and if they are exposed to a large enough number of viral particles,
they will get infected.
We recommend that puppies be restricted from public outdoor
areas until their vaccination series is completed at age 16 weeks.
There is a good week or so period during which the puppy has no
antibody protection leftover from its mother but still is not yet
competent to respond to vaccination. This window is where even the
most well cared for puppies get infected.
INCUBATION
The virus enters the body through the mouth as the puppy cleans
itself or eats food off the ground or floor. A minuscule amount of
infected stool is all it takes.
There is a 3-7 day incubation period before the puppy seems
obviously ill.
Upon entering the body, the virus seeks out the nearest rapidly
dividing group of cells. The lymph nodes of the throat fits the bill
and the virus sets up here first replicating to large numbers. After
a couple of days, so much virus has been produced that significant
amounts of virus have been released free into the bloodstream. Over
the next 3-4 days, the virus seeks new organs containing the rapidly
dividing cells it needs: the bone marrow and the delicate intestinal
cells.
Within the bone marrow, the virus is responsible for destruction
of young cells of the immune system. By killing these cells, it
knocks out the body's best defense and ensures itself a reign of
terror in the GI tract where its most devastating effects occur. All
parvoviral infections are characterized by a drop in white blood
cell count due to the bone marrow infection. Seeing this on a blood
test may help "clinch" the diagnosis of parvoviral infection. Also,
a veterinarian may choose to monitor white blood cell count or even
attempt to artificially raise the white blood cell count in an
infected puppy through treatment.
It is in the GI tract where the heaviest damage occurs. The
normal intestine possesses little finger-like protrusions called
"villi." Having these tiny fingers greatly increases the surface
area available for the absorption of fluid and nutrients. To make
the surface area available for absorption greater still, the villi
possess "microvilli" which are microscopic protrusions. The
cells of the villi are relatively short-lived and are readily
replaced by new cells. The source of the new cells is the rapidly
dividing area at the foot of the villi called the "Crypts of
Lieberkuhn." It is right at
the crypt where the parvovirus strikes.
Without new cells coming from the crypt, the villus becomes
blunted and unable to absorb nutrients. Diarrhea in large quantities
results not to mention nausea. The barrier separating the digestive
bacteria from the blood stream breaks down. The diarrhea becomes
bloody and bacteria can enter the body causing widespread infection
(remember that that virus has simultaneously destroyed the bone
marrow's ability to respond immunologically).
The virus kills one of two ways:
- Diarrhea and vomiting lead to extreme fluid loss and
dehydration until shock and death result
- Loss of the intestinal barrier allows bacterial invasion of
potentially the entire body. Septic toxins from these bacteria
result in death.
HOW IS SURVIVAL POSSIBLE?
Even parvovirus cannot disrupt the entire immune system. Plus, every
day that goes by allows more antibody to be produced. This antibody
can bind and inactivate the virus. Whether survival is possible
amounts to a race between the damaged immune system trying to
recover and respond versus the fluid loss and bacterial invasion.
A puppy with a bloody diarrhea could have a
parasite problem, a virus other than parvovirus, a stress
colitis, or may have eaten something that disagreed with him. It
is important to confirm the diagnosis of parvovirus before
embarking on what could be the wrong treatment.
THE FECAL PARVO ELISA TEST
The ELISA test has become the most common test for parvovirus in
puppies. ELISA stands for Enzyme Linked ImmunoSorbant Assay.
This is sounds complicated and high tech but is actually the
same type of technology that home pregnancy test kits use. The
parvo ELISA test is also a kit and is performed in the vet’s
office in about 15 minutes or less. There are many different
brands and testing is very sensitive in its ability to detect
the actual presence of the virus in stool.
The test has some limitations that are important to realize.
Recent vaccination with a live vaccine (the type of vaccine that
is most effective) may interfere with the test results. This
means that the test may detect the live virus in the vaccine and
show a positive reading when, in fact, the puppy does not have a
parvo infection. Classically, this interference occurs 5-12 days
after vaccination so if a positive fecal ELISA test is obtained
within this period after vaccination, additional tests may be
recommended.
Further, the puppy could be infected but no longer shedding
virus in its stool. Or the virus particles may be so thoroughly
coated with antibodies that they cannot react with the chemicals
of the test. In almost all cases, one can trust a negative ELISA
reading but it is important to realize that no test is perfect.
THE DROP IN WHITE CELL COUNT
Recall that one of the first actions of the canine parvovirus is
to inhibit white blood cell division in the bone marrow. The
virus essentially turns the immune system off before making its
deadly way to the GI tract. This is a feature of parvoviruses in
all species which means that a characteristic drop in white
blood cell count is seen on a blood panel. This characteristic
finding is especially helpful in the diagnosis of a recently
vaccinated puppy as the ELISA test maybe positive from the
vaccine but if the white count is normal, the puppy is probably
not infected. The white blood cell count is commonly monitored
in the treatment of a parvovirus case. If the puppy is not
presented to the veterinarian until later in its disease course,
it is possible to miss the white cell drop and not correctly
make the diagnosis.
ANTIBODY TITERS
There are two types of antibody titer that can be run: IgG and
IgM. With the advent of ELISA testing, titers are not frequently
used in making this diagnosis. The IgG titer is a more long
lasting antibody level. A high IgG titer would probably indicate
active infection in a puppy that is old enough to generate
antibodies and who has not yet received any vaccinations. Most
of the time, the IgG titer simply reflects antibodies generated
by vaccination. The IgM titer reflects recent antibody
production so if a vaccinated puppy had not been vaccinated
recently, a high IgM titer might indicate active infection.
Because parvovirus infected puppies have frequently received
vaccinations in their recent past and are frequently too young
to generate their own antibodies (which is how vaccinated
puppies get infected in the first place), these test results are
difficult to interpret. It is easy to see why the ELISA test
that directly detects presence of the virus has become so
popular.
BIOPSY
Parvovirus lesions in the GI tract are of a classical
appearance. There is no mistaking them under the microscope.
Unfortunately, tissue samples of the GI tract are not readily
available and most infected puppies are not good surgical
candidates. Still, if a puppy has died and the cause is unclear,
submitting samples of the GI tract can generally confirm or rule
out a parvovirus diagnosis.
It is also important to realize
that puppies with parvovirus infection may have concurrent
intestinal parasites or even swallowed foreign bodies. There
will be complicating conditions that must be monitored. This
means that other tests will be required during the management of
the parvo patient. The above tests are simply those that can be
used to confirm the parvovirus diagnosis.
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Treatment for parvoviral infection centers on
support. This means that the clinical problems that come up in
the course of the infection are addressed individually with the
goal of keeping the patient alive long enough for an immune
response to generate. We do not have effective anti-virus anti-biotics
and must rely on the patient’s immune system for cure.
BE PREPARED FOR A 5-7 DAY HOSPITAL STAY AND A SUBSTANTIAL
EXPENSE. INTENSIVE CARE IS NEEDED TO TREAT THIS INFECTION
There are certain basic treatment principles which can be
viewed as “must haves” in addressing the parvo puppy. Beyond
these basics are some “added pluses” which may or may not
contribute to the chance for survival. In order to achieve the
usual survival rate of approximately 75-85%, the basics must be
delivered. If an owner is less concerned about expense and
simply wants to maximize survival chances, some of the optional
treatments may be employed.
THE BASICS
- FLUID THERAPY: One of the ways parvo can kill is via
the metabolic derangements that occur with dehydration. It is
crucial to replace the vast fluid losses (from vomiting and
diarrhea) with intravenous fluids. Fluids are given as a
steady drip rather than simply under the skin so that absorption
into the circulation is direct. Potassium is usually added to
the fluids in order to maintain electrolyte balance. Dextrose
(sugar) is also frequently added as the stress of the disease
may lower blood sugar especially in a very small puppy.
- ANTIBIOTICS: The second way parvo kills is through
bacterial invasion of the circulatory system (“sepsis.”) Since
the GI tract is damaged, antibiotics cannot be given orally.
They are given either as shots or are added into the IV fluid
bag. There are a number of antibiotics which may be selected.
Some antibiotics you may see in use include:
*Cefazolin
*Ampicillin
*Gentamycin
*Amikacin
Our hospital tends to prefer Cefazolin as a basic choice.
- CONTROL OF NAUSEA: Patient comfort is a very important
part of treatment for any disease but is especially important
for parvo treatment as these puppies feel extremely nauseated.
Again, the GI tract is too damaged for oral medication so
medications are given as injections. There are two popular
medications for nausea control:
- Metoclopramide: (best given as a continuous drip in
the IV fluid set up) If used as separate injections, relief
tends to be short lasting and does not provide “around the
clock” control. If a continuous drip is used, nausea control
lasts as long as the drip is running.
- Anzemet: a very strong
nausea control medication which lasts 24
hours per injection.
Injectable antacids (Tagamet, Zantac, or Pepcid) are often
used to prevent ulceration of the esophagus of the esophagus
should protracted vomited be a problem.
MONITORING
The following tests are helpful in adjusting parvovirus
treatment:
- Fecal floatation to rule out worms/internal parasites
The last thing these patients need is a parasite burden
contributing to their nausea and diarrhea.
- White blood cell counts/complete blood counts
One of the first acts of the parvovirus is to shut down the bone
marrow production of immunologic cells (the white blood cells).
White blood cell counts are often monitored as the infection is
followed.
- Abdominal Palpation
Abnormal motility of the intestines occurs with this infection.
Sometimes an area of intestine actually “telescopes” inside an
adjacent area in a process called “intussusception.” This is a
disastrous occurrence as intussusception can only be treated
surgically and parvo puppies are in no shape for surgery.
Euthanasia is usually elected in this event.
- Total blood protein
Protein depletion is common when there is heavy diarrhea. If
blood proteins drop too low, special IV fluids or even plasma
transfusions are needed to prevent massive life-threatening
edema.
EXTRA TREATMENT WHICH MAY HELP:
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PLASMA TRANSFUSIONS In a similar attempt to deliver
anti-bodies to the parvo puppy, plasma from a donor dog who has
survived parvo is sometimes used. The canine origin of such
products reduces the potential for immune reactions but such
plasma is not typically available commercially.
- NEUPOGEN “Neupogen” is the brand name of a
genetically engineered hormone called “granulocyte colony
stimulating factor.” This hormone is responsible for
stimulating the bone marrow to produce white blood cells and
its administration easily overcomes the bone marrow
suppression caused by the parvovirus. A recent study did not
find increased survival with the addition of this product to
the parvo regimen.
- HOME TREATMENT FOR PARVO
Home treatment for parvo infection is a bad idea when compared
to hospitalization and intensive care. Mortality rises
substantially and the heavy diarrhea and vomiting lead to heavy
viral contamination in the home. Still, if financial concerns
preclude hospitalization, home care may be the puppy’s only
chance.& Fluids will have to be given under the skin at home as
will injectable medicines.
IN OUR EXPERIENCE, A PUPPY THAT HAS NOT SHOWN OBVIOUS
IMPROVEMENT BY THE 4TH DAY OF TREATMENT
IN MOST CASES WILL NOT SURVIVE
THE PARVO PUPPY GOES HOME - WHAT YOU
NEED TO KNOW
Medications
Your puppy will be finishing up a course of antibiotics and
may also be on some medication for nausea or diarrhea. It is
important that you give your puppy the medication prescribed
for the full amount of time it has prescribed.
Diet
Your puppy is recovering from some extensive damage to
his/her intestinal tract. It is typical for stool to be a
little loose at first or for no stool to be produced for a
few days as the tract recovers. The stool should gradually
firm up over the first 3-5 days at home and your puppy
should be active and of normal attitude. If the diarrhea
persists, if vomiting occurs or if your puppy seems
depressed, please contact your vet at once for instructions.
Your puppy may be ravenously hungry after going so long
without food. Do not allow the puppy to gorge as this can
result in vomiting or diarrhea. Feed smaller meals separated
by at least an hour or two.
Do not feed table scraps. Stick to the diet recommended
by your veterinarian. A prescription diet may have been sent
home or a home cooked diet may have been recommended (such
as boiled chicken and white rice, or fat free cottage cheese
and pasta). It is important for your puppy’s food to be
easily digestible so stick to the protocol your veterinarian
has recommended.
Exercise
Your puppy should be considered contagious to other puppies
for a good month so it is important to “play it safe” by
restricting trips to the park, obedience school or other
neighborhood areas. If your puppy is less than 16 weeks of
age, he/she should not be allowed in public areas until the
vaccination series is fully completed.
Other Pets
Cats and humans are not susceptible to canine parvovirus
infection. Adult dogs that have been vaccinated are not
susceptible, either. Puppies, however, are at risk. If your
sick puppy was indoors only, wait at least one month before
any new puppies come to your home. If your sick puppy was
outdoors, remember that it can take 7 months before the
virus is eliminated from soil. (Freezing will preserve the
virus so that any time during which the ground is frozen,
that time does not count in this 7 month period.)
Bathing
Your puppy may be bathed any time as long as you do not
allow him/her to get cold or chilled after the bath. Bathing
will reduce the amount of virus left on the puppy’s fur and
will help reduce contagion.
Resuming Vaccines
Follow your veterinarian’s recommendations. Your puppy
cannot be re-infected with this virus for at least 3 years
(and probably is protected for life simply by virtue of this
infection) but there are other viruses that your puppy
should be protected against. Your veterinarian will give you
a vaccination schedule to adhere to for the future.
There should be no permanent ramifications due to this
infection. The recovered puppy should lead a normal life
once the recovery period is completed (1-2 weeks)
IF YOU HAVE ANY QUESTIONS ABOUT YOUR PUPPY’S CARE
AFTER DISCHARGE CONTACT YOUR VETERINARIAN’S OFFICE FOR
ASSISTANCE.
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