| Parvo Virus Veterinary & Aquatic Services Department, Drs. Foster & Smith, Inc. |
Parvovirus
Canine parvovirus 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 and is caused by a pathogen
called canine parvovirus, Type 2 (CPV-2). In 1980, the original strain of CPV-2 was replaced by CPV-2A and in 1986,
another variation called CPV-2B appeared. Today, CPV-2B has largely replaced the previous strains as the most
common isolate. Since all of these strains are similar, we will lump them together and refer to them as CPV-2
(parvo). 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 in both breeding and veterinary circles. We hope that with a
better understanding of the disease, pet owners will be able to make good husbandry decisions that will help
prevent and reduce the spread of this disease.
How is parvo spread?
CPV-2 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. 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. The
normal incubation period (time from exposure to the virus to the time when signs of disease appear) is from 7-14
days. Active excretion of the virus in the feces can begin the third day after exposure, often before clinical signs
appear, and may last for one to two weeks after the onset of the disease.
Symptoms
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 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 CPV-2 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. CPV-2 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 CPV-2 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.
Diagnosis
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 newer and
simpler test of the fecal matter with an enzyme-linked immunosorbent assay antigen test (ELISA) are also
available through most veterinary clinics. Testing of all suspect cases of Parvo is the only way to correctly
diagnose and treat this disease.
Treatment
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.
Antibiotic therapy is usually given to help control secondary bacterial infections. 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. 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.
Immunity and vaccination
If a puppy recovers from CPV-2 infection, it 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. Although some people have expressed concern about
the possibility of attenuated 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 colostral 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 a couple 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 litter.
A study done in 1985 in a cross section of different puppies showed, that 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.
There is a newer Type 2 strain of vaccine known as a high titer, low passage vaccine. When using this vaccine, the
percentages of puppies immunized are much higher at an earlier age. Some early studies are claiming 90% of the
puppies are protected at 9 weeks of age and almost 98% protected at 12 weeks when this new Type 2 parvo
vaccine is used.
When we examine all of the information about maternal derived antibodies, windows of susceptibility, throw in
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. Drs. Foster and Smith recommend a protocol that will help protect the widest range of dogs. We
realize that with our protocol, 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.
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. Using the newer high titer vaccines may shorten the window of susceptibility on many puppies. 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. As new information on this disease and vaccines
become available, we will continue to update this article in hopes of keeping you as informed on Parvo as possible.
Copyright © 1997-2004, Drs. Foster & Smith, Inc. All Rights Reserved.
Reprinted from PetEducation.com.
Canine parvovirus 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 and is caused by a pathogen
called canine parvovirus, Type 2 (CPV-2). In 1980, the original strain of CPV-2 was replaced by CPV-2A and in 1986,
another variation called CPV-2B appeared. Today, CPV-2B has largely replaced the previous strains as the most
common isolate. Since all of these strains are similar, we will lump them together and refer to them as CPV-2
(parvo). 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 in both breeding and veterinary circles. We hope that with a
better understanding of the disease, pet owners will be able to make good husbandry decisions that will help
prevent and reduce the spread of this disease.
How is parvo spread?
CPV-2 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. 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. The
normal incubation period (time from exposure to the virus to the time when signs of disease appear) is from 7-14
days. Active excretion of the virus in the feces can begin the third day after exposure, often before clinical signs
appear, and may last for one to two weeks after the onset of the disease.
Symptoms
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 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 CPV-2 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. CPV-2 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 CPV-2 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.
Diagnosis
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 newer and
simpler test of the fecal matter with an enzyme-linked immunosorbent assay antigen test (ELISA) are also
available through most veterinary clinics. Testing of all suspect cases of Parvo is the only way to correctly
diagnose and treat this disease.
Treatment
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.
Antibiotic therapy is usually given to help control secondary bacterial infections. 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. 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.
Immunity and vaccination
If a puppy recovers from CPV-2 infection, it 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. Although some people have expressed concern about
the possibility of attenuated 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 colostral 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 a couple 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 litter.
A study done in 1985 in a cross section of different puppies showed, that 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.
There is a newer Type 2 strain of vaccine known as a high titer, low passage vaccine. When using this vaccine, the
percentages of puppies immunized are much higher at an earlier age. Some early studies are claiming 90% of the
puppies are protected at 9 weeks of age and almost 98% protected at 12 weeks when this new Type 2 parvo
vaccine is used.
When we examine all of the information about maternal derived antibodies, windows of susceptibility, throw in
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. Drs. Foster and Smith recommend a protocol that will help protect the widest range of dogs. We
realize that with our protocol, 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.
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. Using the newer high titer vaccines may shorten the window of susceptibility on many puppies. 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. As new information on this disease and vaccines
become available, we will continue to update this article in hopes of keeping you as informed on Parvo as possible.
Copyright © 1997-2004, Drs. Foster & Smith, Inc. All Rights Reserved.
Reprinted from PetEducation.com.
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