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Meet Parvovirus
PARVOVIRUS
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?
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.
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
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.
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.
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.
Urine specific gravity/Azosticks
In order to assess the effectiveness of the fluid therapy, some objective evaluation of dehydration is useful. If adequate IV fluids have been provided then the urine produced will be dilute (as measured by “specific gravity”) and azosticks measures of protein metabolites (which build up in the blood stream) should be at normal levels.
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.
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.
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.)
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.
How do I prevent my puppy from getting parvovirus?
VACCINATION. By vaccinating puppies starting at 6 wks old, and getting boosters every 3-4 weeks until 12-16 weeks old, you can normally prevent the virus from ever infecting your puppy. As mentioned above, maternal antibodies can be present in some dogs beyond 12 weeks old so boosters are VERY important to ensure protection. Adult dogs with a booster vaccine are nearly guaranteed never to become infected with parvovirus and many other viruses included in the combo vaccines. A typical combo vaccine and exam in our area is $50; parvo treatment can be $500+ and in a 24hr care emergency hospital, several thousands of dollars can be spent with no guarantee that the puppy will survive.
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?
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.
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
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.
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.
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.
Urine specific gravity/Azosticks
In order to assess the effectiveness of the fluid therapy, some objective evaluation of dehydration is useful. If adequate IV fluids have been provided then the urine produced will be dilute (as measured by “specific gravity”) and azosticks measures of protein metabolites (which build up in the blood stream) should be at normal levels.
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.
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.
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.)
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.
How do I prevent my puppy from getting parvovirus?
VACCINATION. By vaccinating puppies starting at 6 wks old, and getting boosters every 3-4 weeks until 12-16 weeks old, you can normally prevent the virus from ever infecting your puppy. As mentioned above, maternal antibodies can be present in some dogs beyond 12 weeks old so boosters are VERY important to ensure protection. Adult dogs with a booster vaccine are nearly guaranteed never to become infected with parvovirus and many other viruses included in the combo vaccines. A typical combo vaccine and exam in our area is $50; parvo treatment can be $500+ and in a 24hr care emergency hospital, several thousands of dollars can be spent with no guarantee that the puppy will survive.
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Parvovirus
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