Infectious Diseases of Dogs - Parvovirus


Canine Parvovirus

Quick Facts:

As the name implies, parvovirus is a viral illness. Effective vaccination is possible. Parvovirus is predominantly a disease of young puppies between 6 weeks and 6 months of age. Without treatment approximately 80% of affected puppies will die. With proper treatment approximately 85% of affected puppies will live. The virus may persist in the environment for up to 5 months. Infection generally follows exposure to infected feces. The incubation period for the illness is 4 to 14 days. The major clinical signs are vomiting and diarrhea. The diarrhea is usually yellow to yellow gray at first but quickly becomes blood tinged or dark red in most cases


Canine parvovirus is a DNA virus. There are two major strains, canine parvovirus 1 (CPV-1)and canine parvovirus 2 (CPV-2). The CPV-2 strain has mutated several times and there are CPV-2a, CPV-2b and CPV-2c strains. The CPV2-a to c strains have the ability to infect both dogs and cats but clinically significant infections of domestic cats have not been reported up to this time. The virus is shed in the feces of infected dogs. It is passed to another dog through the nasal or oral tissues after exposure. The virus begins to be shed about 4 days after exposure. There may not be clinical signs at the time that shedding starts. Parvovirus attacks rapidly dividing cells. In growing animals the most rapid cell division occurs in the lining of the gastrointestinal tract. Puppies who have other infections with worms, bacteria or intestinal viruses seem to be affected more severely than puppies who do not have these problems. Another site of rapid cell division is the myocardium, or heart muscle tissue. Very young puppies, usually less than 8 weeks of age, that are infected with parvovirus may suffer severe myocardial problems and die as a result of them. When this happens it may affect the entire litter of puppies.


There is a temptation to blame almost any case of vomiting and diarrhea in a young puppy on parvovirus but it is important to keep in mind there are many other causes of these symptoms. It can be hard to definitively diagnose parvovirus in a clinical setting. Most puppies with parvovirus seem very ill. They are usually noticeably depressed. There is usually vomiting and severe diarrhea. White blood cell counts are suppressed, especially the neutrophils. There are tests for parvovirus but false positives can occur within 5 to 12 days of vaccination and false negative tests occur, as well. A combination of suspected clinical symptoms, a positive parvovirus test and low white blood cell count comes close to ensuring a proper diagnosis. If two out of three of these criteria are present it is likely but not certain that parvovirus is present. Adult dogs that become infected with parvovirus generally have no clinical signs or perhaps transient diarrhea. While these dogs may shed the virus they are not severely affected by it. It is rare to see confirmed clinically significant parvovirus in a dog over 18 months of age.


Treatment for parvovirus is supportive. There is no direct anti-viral medication for this disease. Treatment efforts are focused on keeping puppies hydrated, making sure that their electrolyte balances are relatively normal and preventing secondary infections that occur due to the tissue damage and low white blood cell counts. There are a number of things that can be helpful when treating parvovirus: Antiemetic drugs - ondansetron, dolasetron and maropitant (Cerenia Rx) Intravenous or subcutaneous fluid therapy Broad spectrum antibiotics – note that this is an important part of treatment even though this is a viral illness! Hyperimmune plasma or antiendotoxin sera (Septi-serum Rx) Flunixin (Banamine Rx) may be beneficial if puppies become septicemic (have widespread bacterial infection) If a puppy survives the first four days of treatment it is likely that it will survive parvovirus infection. Vaccination and


Puppies receive protection from parvovirus in the colostrum, or first milk produced by their mothers. This protection is variable depending on whether the mother had antibodies against parvovirus and how much colostrum a puppy received in its first 24 hours of life. In some cases this protection is not conferred. This variability in maternal protection is the major reason a series of vaccinations is given to puppies. A starting date for vaccination is picked based on the puppy’s ability to respond to infection and the likely timing of exposure to the disease. In general the first vaccination in the puppy series is given between 6 and 8 weeks of age. Only a portion of puppies are capable of responding to this initial vaccine series but since it isn’t practical to determine in advance which puppies can respond, all are vaccinated. The puppies that need the protection get it and the rest do not benefit from the first vaccine. At least 2 weeks later and preferably 3 to 4 weeks later, a second vaccination is given. A larger percentage of puppies respond to this vaccine, but not all of them. The vaccination series is continued at 3 to 4 week intervals until it is likely that all puppies who can respond to vaccination have done so. The number of vaccinations in the series and the age at which the final puppy series vaccination is given will depend on the type of vaccine used, the breed of the puppy, the puppy’s lifestyle, the owner’s experiences and the veterinarian’s experiences with the disease. Vaccines are produced by several vaccine manufacturers for prevention of parvovirus. Most of the currently available vaccines are high antigen vaccines which break through maternal antibody protection earlier than the the original parvovirus vaccines. These vaccines also provide protection in most puppies when given between 12 and 14 weeks of age. The older parvovirus vaccines had to be given until 16 or even 20 weeks of age to ensure maximum protection. Of the currently available vaccines still in use only the Vanguard ™ series of vaccines from Pfizer Animal Health ™ are the older type of vaccine (as of 2006, per “Infectious Diseases of the Dog and Cat” by Greene). There is a period of time, between 2 and 3 weeks, when the parvovirus strains found in most infections can cause disease before there is a chance for vaccinations to work. At the present time there is no way to avoid this period. More frequent vaccination is not helpful and vaccinations given closer than two weeks apart may even impair immunity. For this reason, it is best to avoid exposure to potential sites of infection, such as dog parks, dog shows and kennels until after the last vaccine in the series. It is also important to remember that the veterinarian’s office is a potential site of contamination, especially the area outside the veterinary hospital. Puppies should be walked directly to the door and should be kept away from other puppies in the waiting room that appear to be ill. Veterinary hospitals and kennels try very hard to properly clean up after incidences of diarrhea and in areas in which exposure can occur but it is hard to do this perfectly. Parvovirus is very hardy in the environment. If your house becomes contaminated by the virus clean any surfaces that can be cleaned with chlorine bleach diluted 1 oz of bleach to 32 oz of water. The disinfectant potassium peroxymonosulfate (Trifectant ™ or Virkon ™) is also effective. It is extremely hard to disinfect a yard. Realistically, if your yard has been potentially contaminated with parvovirus it would probably be best not to get a new puppy and expose it to the yard for at least six months and nine months would be better. Areas of the yard that are exposed to sunlight will require less time for the virus to die than areas of the yard that are shaded, moist and sandy. At the present time there is not a disinfectant product marketed for use in yards that has been proven to be effective against parvovirus.

Mike Richards, DVM 10/21/2007 For information on parvovirus in shelter situations:


Parvovirus is a viral disease of dogs. It affects puppies much more frequently than it affects adult dogs. The virus likes to grow in rapidly dividing cells. The intestinal lining has the biggest concentration of rapidly dividing cells in a puppy's body. The virus attacks and kills these cells, causing diarrhea (often bloody), depression and suppression of white blood cells -- which come from another group of rapidly dividing cells. In very young puppies it can infect the heart muscle and lead to "sudden" death. This is a very serious disease. Some puppies infected with parvovirus will die despite prompt and adequate treatment. While no extremely accurate statistics are available, a good guess is probably that 80% of puppies treated for parvovirus will live. Without treatment, probably 80% or more of the infected puppies would die.

Due to the high death rate, parvovirus gets a lot of free publicity. Many people just assume that any case of diarrhea in a dog is from parvovirus. This is not true. There are a lot of other diseases and disorders that lead to diarrhea. If you have a puppy, don't take any chances. Have your puppy examined by your vet if diarrhea is a factor in any disease. It is better to be safe than to be sorry.

Mike Richards, DVM

Parvo - Is it possible in adult vaccinated dogs

Question: I have a question that I hope you have time to answer. Do you know anything about late onset parvo? I ask because there have been a couple of cases of it here and at least one of the dog's vaccination history is well documented. The dog is a Maltese about 7 years of age and had annual vaccinations. I haven't been able to get all the facts I would like on the other dog but it appears that it too is definitely an adult. What is questionable is if the dog had actually received the full puppy series. Saludos, Charlotte

Answer: Charlotte- Whether or not clinically apparent parvovirus actually occurs in dogs over the age of 14 months or so is a difficult question to answer. These are the things that make it seem unlikely: 1) Parvovirus likes to attack rapidly dividing cells. In a puppy, the entire intestinal lining, from the tip of the villi to the depths of the intestinal folds divides rapidly, with almost a total turnover of cells in 3 to 5 days. The myocardium has rapidly dividing cells that are sometimes affected in very young puppies (usually less than 9 weeks of age or so). White blood cell numbers drop dramatically because the cells they divide off from are also rapidly dividing cell lines. These are the focus of the virus attack because these are the only cells dividing rapidly enough for the virus. In adult dogs, only the tips of the villi remain rapidly dividing and these can all be sloughed without producing clinically significant disease (in most cases no signs at all will be seen). 2) Parvovirus vaccination probably lasts for life if good immunity is ever achieved. In most dogs, a single injection of a modified live parvovirus vaccine given after twelve weeks of age ( new high titer vaccines) or sixteen weeks of age (older vaccines) will confer immunity. The one year booster shot should strongly bolster this and if a puppy didn't respond properly to the puppy vaccinations for some reason (like having a heavy parasite load or another viral illness) the one year vaccination should provide good immunity. This means that a dog that has had the puppy series and/or any boosters of that series should have good immunity unless its immune system just doesn't respond properly. 3) Most dogs who are reported to die of parvovirus actually die from an undetermined cause, because any post mortem examination that is done doesn't include taking intestinal tissue samples to confirm that the virus was present. Testing for parvovirus using in-house test kits is compromised by vaccination (will be positive in many vaccinated dogs, regardless of whether they actually have parvovirus.

My personal opinion is that parvovirus probably does cause disease on a rare basis in adult dogs, probably when it happens to coincide with another illness that weakens the same tissues. I really believe these cases are rare, though. I think that most of the reports of adult onset parvovirus are situations in which a look alike illness occurred and it was easy to blame parvovirus and it is not usually confirmed in a manner that is very conclusive. Vaccination for parvovirus provides protection for a long time and probably does so for life. This would be especially true in a area in which there is widespread contamination with parvovirus particles because exposure to these would provide small amounts of stimulation (what is a vaccination?) to the immune system, encouraging it to maintain its competency in fighting the disease. If any of this is confusing, let me know. Mike Richards, DVM 10/14/2002

Parvovirus in dogs

Background Facts: Parvovirus is the name of a family of viruses. There are parvoviral illnesses in many species but most of them have other names, such as panleukopenia in cats. For the most part, when you hear the terms "parvo" and "parvovirus" the reference is to this disease in dogs.

Parvoviruses attack rapidly dividing cells preferentially. In most cases, the only cells in the body which are replaced frequently enough to be attacked are the cells lining the intestine. In very young puppies the heart muscle is also susceptible. In dogs less than one year of age the entire cellular lining the intestine is replaced every five days or so. In older dogs, only the tip of the villi in the intestines are replaced, at about the same rate. So parvovirus is a disease that is clinically severe in puppies but may be an inapparent illness in an older dog.

Cause: canine parvovirus

Infectivity: Spread through contact with the stool of infected puppies or dogs. Parvovirus can live in the environment for several weeks to months. Avoid areas in which many dogs defecate when walking puppies

Age/Sex/Breed Differences: Clinical illness is almost always confined to dogs less than 14 months of age. Beagles, rottweilers and doberman pinschers may be more susceptible than other breeds.

Symptoms: Depression is usually the first sign of this illness. This is followed shortly by severe diarrhea and often vomiting. The diarrhea usually contains digested or partially digested blood giving it a pungent odor. Affected puppies often have very low white blood cell counts. Severe dehydration can occur rapidly with this illness.

Diagnosis: There are accurate tests for this virus in stool but there can be false positive results in recently vaccinated puppies, which is the case for most puppies in this age range. Depression, diarrhea and low white blood cell counts in a puppy are reason enough to treat as if parvovirus is present.

Treatment: Intravenous fluid therapy is the mainstay of treatment for this illness. Administration of serum and newer colloidal fluids along with traditional fluid therapy seems to help puppies survive. Antibiotics are necessary to prevent secondary bacterial illnesses. Since Clostridium species bacteria are a common secondary problem, amoxicillin and antibiotics with similar spectrum are often used.

Prognosis: Untreated puppies have an 80% fatality rate. In treated puppies the fatality rate hovers around 20% but seems to be improving with the use of colloidal fluids.

Prevention: Vaccinations remain the mainstay of prevention. Parvovirus is still capable of causing infection for several days prior to the time the vaccines can work to protect against the disease, though. For this reason, it is best to avoid areas that might be contaminated with parvovirus until after the puppy has received a vaccination at twelve weeks of age or older. It is recommended that vaccination start at 6 weeks of age and that puppies receive vaccinations at two to four week intervals until they are 12 to 16 weeks of age. We prefer to vaccinate at 6, 9 and 12 weeks for this virus but puppies with high exposure potential may have to be vaccinated more often.

Michael Richards, DVM 9/2000

Puppy immunity and Parvo

Question: Dear Dr. Richard,

I really don't know where to begin. Please bear with me... I'm currently working in Korea and about two months ago I got a Daschshund puppy (said to be ~3 months old). The day I bought her, Pepper, I took her over to a friend's house for a few hours before bringing her home (my friend had a 5 month old papillon). But the minute I brought her home she went diarrhea and then again the next day so I called the pet shop and they told me that this could happen due to stress coming from being placed in a new environment. Is this true?

Well, I took her back to the pet shop and they took care of Pepper for several hours and told me that her stool was normal so that I could take her mistake. As soon as I brought her home this time, she started vomitting. I called the pet shop again and this is when they told me to take her to a veterinarian. I'm not sure how pets (puppies) are sold in the States but here in Korea, they're sold BEFORE they have all their shots. I didn't know this. When I took her to the vet, they diagnosed her with Parvo after performing a parvovirus strip test (accustrip by Jant Pharmacal Corporation).

The doctors did all they could with IVs, antibiotics, etc. and Pepper seemed to be doing better but after hanging on for about a week she passed on.

I confronted the pet store about Pepper dying from parvo and that since it is a viral infection there is an incubation period so it's very likely that she had the virus BEFORE she came home with me. But the pet shop refused to take any responsibility and told me that it was due to my carelessness that Pepper died and that if parvo is such a contagious disease then why didn't her brothers and sisters get it, too. And that I could see for myself that they're alive and healthy anytime I want. They also blamed my bringing Pepper over to my friend's place and having contact with the papillon.

I knew that I wasn't going to get anywhere arguing with the pet shop so I've decided to go to court. I know, it sounds a little extreme but after Pepper died, I found out that there is a serious problem in Korea with puppies being sold to families/consumers dying within days or weeks after coming home.

For my specific case, I will need to prove that even with puppies in the same litter some can die from parvo and others can survive. I read on the VetInfo homepage about a person with a surviving puppy of a litter that had parvo. I'm taking this approach because it's impossible to pinpoint exactly when Pepper was infected since she was in different places.

Has there been any research done on puppy immunity and how the immunity of puppies in the same litter could vary? If you know of any could you tell me where I can maybe find it? I also wanted to ask for your permission on incorporating some information on VetInfo (it will be referenced).

Thank you for reading my long message and I look forward to hearing from you soon.

Best regards, Hannah

Answer: Hannah-

There is no question that only part of a litter of puppies can be affected by parvovirus, including only one puppy, if that is really the situation. This is why:

Puppies do not have antibodies to diseases, except in very small amounts, from their mother while in the uterus, like members of some species (humans, for instance). Antibodies to protect against disease are passed from the mother to the puppies through the first milk produced, called the colostrum. Puppies can only absorb antibodies for the first 24 to 36 hours of life. After that, they can no longer absorb antibodies.

There are a number of ways that this process of passing on antibodies can fail. The puppy may not nurse the first day of life. The mother may self nurse or leak colostrum, using it up. The puppy may be the last puppy to nurse and the antibody containing colostrum may have been used up by the other puppies. So one puppy may have very good protection against parvovirus, while another puppy has little or no protection. Over time, the maternal antibodies are broken down, used up or otherwise rendered inactive by the puppy. As this protection wears off, the puppy becomes susceptible to the disease.

The reason that a series of vaccinations is given is due to the way antibody protection wears off. When the first vaccinations are given, usually around 6 weeks of age, only 10 to 25% of the puppies have lost maternal antibody protection. ONLY these puppies are protected by the vaccination. In the others, the maternal immunity destroys the vaccine virus so the puppy does not develop immunity to it. At 9 weeks of age, probably 50 to 75% of puppies have lost maternal protection to parvovirus. So this time, most puppies are protected by the vaccine but 25% or more still have enough maternal antibody to interfere with the vaccine. Finally, at twelve weeks of age, most puppies can be protected by the new parvovirus vaccines. With older vaccines, it may be sixteen or even twenty weeks of age before the vaccine is effective since it is not as capable of overcoming maternal immunity.

That is why one puppy in a litter, or part of a litter, can develop parvovirus, while others do not.

In your puppy's case, though, there is more evidence that the parvovirus was already present, since the puppy showed signs on the first day you got her. Like many viruses, parvovirus has an incubation period, or a period of time that it builds up in the body prior to the time that clinical signs appear. For parvovirus, this time period is at least four days and may be as long as seven days.

In addition to this, the test for parvovirus depends on the presence of virus that is shed into the digestive tract and excreted. After infection, it takes three to four days for the virus to be shed in the stool, so the test should not be positive in an unvaccinated puppy until three days after the time the puppy was infected. Since you took her to the veterinarian on the second day, if I understand the message correctly, there should not have been time for a positive test result unless the puppy was already infected.

So I think that there is no question that your puppy was infected at the time that you purchased her. Any veterinary textbook that includes information on parvovirus should have most of this information in it, so you should be able to find an authoritative source with your veterinarian's help.

I am sorry that you had this experience.

Mike Richards, DVM 9/10/2000

Parvo vaccinations and older dogs

Question: I am a subscriber and would like to know what your opinion is on giving older pets the yearly Parvo vaccination. I have a Doxie who turned 14 last Nov. and I got a vaccination reminder for her this week. What are the pros and cons of the vaccine at this age, in your opinion? Thank you Dr. Mike. Dixie

Answer: Dixie-

There are some published reports which suggest that older dogs have a decrease in immune system competency which makes them more susceptible to disease. From this view, yearly vaccination seems like a good idea.

On the other hand, there is good evidence that parvovirus vaccination has a very long duration of effect and that older dogs are not very susceptible to this infection. Most veterinarians do not vaccinate just for parvovirus, though. Usually this vaccination is combined with distemper, adenovirus and parainfluenza and often with additional infectious agents, such as leptospirosis. When looking at the combination vaccines, some of the components have long durations of action (distemper) and some very short actions (leptospirosis). To provide protection for all components of the vaccine it may be necessary to vaccinate yearly, or even more often than that. Figuring out which diseases included in the vaccine are important to your area and to your pet can guide these decisions.

In dogs, vaccines cause some adverse reactions. There can be immediate sensitivity reactions such as anaphylactic shock, which is a severe, life threatening reaction. These are rare and usually happen in the vet's office where treatment is available, but they do occur. Immune suppression occurs a few days after vaccination and lasts a week or two. Usually this does not cause any problems, though. Immune mediated hemolytic anemia occurs in some dogs as a result of vaccinations and this is a very serious side effect. It is not a common occurrence but it is a concern. These are the reasons that work is being done to determine the length of time that vaccines provide protection, so that it will be possible to better evaluate the necessity of vaccination for a particular patient.

The only thing I can really say at this point is that you have to assess the risk in your area, then consider your pet's risk in relation to that (housedog vs. showdog, for instance) and then make the most informed decision you can. If you decide not to vaccinate, do not skip the physical exam. These are important in older patients.

I am hoping to be able to be much more specific about these recommendations soon, as more information about the duration of vaccine immunity becomes available. When it is available we will definitely be putting it online and in the VetInfo Digest.

Mike Richards, DVM 8/31/2000

Parvo incubation

Question: I have a friend who was caring for someone's puppy and the puppy developed Parvo. The puppy's people blamed my friend. Is there a known incubation period for Parvo?

Thanks doc.

Answer: S-

The incubation period for parvovirus is between 4 and 14 days. This is the amount of time from the exposure to the virus until clinical signs are obvious. Puppies have detectable virus in the blood stream prior to four days and they shed the virus in their stool for up to two weeks after they seem to be fully recovered.

This virus is very hard to avoid and it is not really fair to blame anyone for the puppy's exposure to the virus. The virus can last several months in the environment and puppies are easily infected. Vaccination is the best protection against this disease but it doesn't always work, because there is a brief period of time (about a week) during the puppy's life when the virus can overpower vaccination even when it has been properly administered.

Hope this helps your friends understand this disease a little better. If you need additional information, let me know.

Mike Richards DVM 8/10/2000

Parvo - surviving puppy in litter

Question: Dr. Richard's: This is concerning a puppy that was one of a litter that had PARVO. Two of the puppies died. The surviving puppy showed no signs of PARVO. Will the surviving puppy be contagious to other puppies if taken to another environment? Thank you for any suggestions and help that you can give me. Constance

Answer: Constance-

The surviving puppy may or may not shed the virus in its stool. The most likely scenario is that the puppy got more maternal immunity than the other puppies and did not become infected with the virus, at all. This happens because puppies absorb colustrum, which contains all the antibodies they get from the mother, for about 24 hours after birth. After that time, the mother's milk does not provide much additional protection. So puppies that nurse last, do not nurse well may be deprived of antibodies that they need. In addition, if the mother lactates a lot prior to the delivery of the puppies, she may not have much colostrum at the time the puppies are born, since it is the first milk produced. If the surviving puppy had enough antibody protection to kill the virus, there won't be any fecal shedding.

The environment will be contaminated due to shedding of the virus in the stools of the other puppies, though. This is a good reason to remove this puppy from that environment. The virus can last for months in the environment in some cases.

Sometimes adult dogs are infected with parvovirus and show very few, or no, clinical signs of the illness, despite shedding it in their stool. There is a small chance the surviving puppy may have had a similar course of this illness. In that case, the virus will be shed in the stool for about 12 days. Just to be cautious, it would be best to keep this puppy isolated from others for that long, if possible.

There is also a chance that the other puppies did not have parvovirus. This disease has pretty typical symptoms associated with it, including dark brown to red liquid diarrhea, an odor that is highly suggestive of the disease, low white blood cell counts during acute infection, dehydration and vomiting. However, many other diseases cause at least some of these signs, too. Parvovirus is so common that it gets blamed for many puppy's illnesses when it is not actually the problem, just because it is usually the most likely suspect. If this happened, there is a chance that the puppy could be a carrier of a different disease. For most diseases involving puppies and diarrhea there are not chronic carrier states, with giardia infection being one exception. Rechecking a stool sample prior to letting the puppy mingle with new friends might be a good idea, too.

We do not confirm very many cases of parvovirus through testing procedures that are definitive and I suspect not many vets do. The parvovirus tests may be falsely positive within a few days of vaccination, which is often the case in puppies, so unless no vaccinations occurred prior to the illness, I have a hard time being sure this test is meaningful.

I think that the odds are in your favor that the puppy will not infect others if there is no illness and if there is no sign of giardia or intestinal worms on a fecal exam and you have waited at least twelve days prior to letting it mingle with other puppies.

One last thing to consider is that if the puppy did get a lot of maternal antibody protection it will still wear off eventually. In most puppies there is a period of several days when exposure to parvovirus will usually cause disease even though the puppy has been properly vaccinated up to that point. The virus is just stronger than the vaccine during this time period. So this puppy is still at risk of developing parvovirus if it is still exposed to places that the other puppy's stools may have been.

I hope this last puppy does well. Plan to go ahead and give it its vaccinations on the normal schedule your vet recommends.

Mike Richards, DVM 5/2/2000

Types of Parvo

Question: As a subscriber, I would appreciate your comments on new more virulent "strains" of PARVO. Many individuals I know have been following a trend in immunizing infrequently and avoiding the use of MLV vaccines. I am aware of the many problems and side effects that vaccines can cause and and am considering going to a 3 year immunization program for my dogs. However, I will only do so after a thorough eval of my dogs life style, age, breed, health status and discussion with my vet. With a recent outbreak of PARVO in my area there seems to be a generalized hysteria about new and virulent strains and whether the current vaccines (either MLV or killed) will be effective. My understanding is there are only two types of PARVO - CPV1 and CPV2. Could you please comment on whether there are new and more virulent strains of PARVO now appearing and your opinion of the state of vaccination as it currently stands for dogs and for PARVO in particular.

Thanks, C.

Answer: C.-

I am unaware of any substantiated evidence of new parvovirus strains. There have been persistent rumors of new strains of parvovirus ever since the disease first occurred in the early 80's. It is obviously possible that a new strain could occur and that it may take a while for veterinarians to become fully informed, but so far, these rumors have simply been rumors -- no fact. As far as I know, Type 2 parvovirus (there are actually at least three strains of Type 2 virus but they have been recognized for some time) causes the clinical illness seen in dogs.

Many species of animals, including humans, have parvoviral illnesses and I think that some of the worry over new strains comes from misinterpreting literature relating to other species as being relevant to dogs.

There has been a lot of work in recent years on new vaccine formulations and the newer vaccines are more potent (have a higher antigen load) and can produce immunity in the face of maternal antibody protection at an earlier age. These new vaccines will produce reliable immunity in most puppies by 12 weeks of age but it is still considered to be prudent to vaccinate high risk breeds like rottweilers and beagles at 15 weeks of age or later. These vaccines are not based on new strains of parvovirus, they use higher vaccine virus numbers to achieve better results. Killed parvovirus vaccines are of limited value. This is a disease for which there is strong justification for using a low passage, high titer, modified live virus vaccine. Many puppies die despite good care once infected and the cost of treatment is high even in puppies that survive. Protection must occur as close to the loss of maternal immunity as is possible. Modified live vaccines are the only way to ensure that this type of protection occurs.

My personal opinion on parvovirus vaccination is that puppies should be vaccinated starting at about six weeks of age at intervals no closer than two weeks apart, until they are at least twelve weeks of age for most breeds and fifteen weeks of age for breeds that seem especially susceptible to the virus, using one of the newer vaccines (there are several, ProGuard (tm) is probably the best known but Solvay's and Meriel's vaccine strains are also good and there are probably others). We vaccinate at 6, 9 and 12 weeks, preferably and adjust the schedule if we see puppies for the first time after six weeks of age but generally use a 3 to 4 week interval between vaccinations. I think that dogs should receive a booster one year after the initial puppy series. I think that further vaccination is probably unnecessary for parvovirus, personally, but this is based on evidence that parvoviral diseases in others species appear to cause lifelong immunity if an animal survives infection or is adequately vaccinated. And based on the fact that I have only seen one adult dog with confirmed parvovirus in twenty years of veterinary practice and I do autopsy exams whenever clients will allow it in suspicious cases. So I'd be comfortable with an every three year vaccination schedule for this virus if there was a desire to be cautious about protecting for it.

Just about every veterinarian I know can relate at least one case of an adult dog that appeared to be infected with parvovirus and some have seen a handful of cases --- but there is no credible information that I have ever seen that suggests that adult dogs have clinically apparent parvoviral infections on anything approaching a regular basis. This is primarily a disease of puppies and young dogs under a year of age.

There do seem to be outbreaks that are more severe than others and I can't explain why this occurs. To some extent I think that it is simply perception. To explain why I think this can happen let me relate my personal experience with parvovirus.

When this was a new disease, I treated about thirty to forty puppies before losing one ( I used to know the exact number - it may be on our website somewhere). Every vet I talked to was losing about 30 to 40% of the puppies they were treating. I honestly thought that everyone else must be treating the disease incorrectly and even told a couple of my colleagues so. Then I lost about fifteen puppies in a row. The statistics caught up with me all at once. For a while I thought I had lost my ability to practice and was going to be a total failure from that time on. I apologized to all of my colleagues who I had talked to previously. Since this odd start, we have probably lost about 20 to 30% of the puppies we try to treat but this percentage keeps improving with improved knowledge of how to treat the disease as time goes on. It is easy to be misled by small numbers of cases and the experiences of a single veterinarian or single dog breeder -- it is like flipping a coin, eventually the heads and tails will come out even but there will be streaks of all heads or all tails that seem to defy the odds.

With all of that said, at the present time we continue to vaccinate most dogs yearly at the present time. We have gone to every three year vaccinations in cats due to the higher risk of complications from vaccinations, in cats. As time goes on and good studies are published on the duration of canine vaccinations, we will move toward longer vaccination intervals if it seems appropriate.

We have noticed a trend in cat owners to skip the yearly physical exam when vaccinations are not due. We view this as a major mistake due to the benefits of finding and treating problems early and we are doing the best we can to educate cat owners on this subject. Veterinarians are fearful of changing vaccine schedules precisely for this reason. We have done such a good job promoting the vaccine as the reason for a yearly visit that pet owners forget the value of the physical exam. It is part of the reason we have been slower to adopt a longer vaccination interval in dogs. Ethically, though, I will have a hard time not going to longer intervals if duration of immunity studies do confirm that longer intervals are safe. I just hope we succeed in re-educating our clients to the value of a yearly physical exam before this occurs.

Hope this helps rather than confuses you.

Mike Richards, DVM 11/1/99

Parvovirus infection

Q: We have three dogs. One is 17, one is 4 and the other one we just got and she is about four to six months. We have had her about a month and the people we took her from were going to throw her in the woods. They did say that she had her first shots and we believed them. The dog was acting fine until yesterday and then she started not eating and if she drinks she vomits a watery mucus. She seems to just want to lay around and we can't get her to do anything. Does this sound like parvo to you?

If she has parvo can my other two dogs get it? To be honest they do need their shots. What can I do to prevent them from getting it? We are hoping she will be better by morning and she is just ill but not sure. We do intend on calling our vet if she is not any better but was hoping that you could answer these questions for us.

Thank you!

A: t-

Parvovirus infection often starts with depression and lethargy, followed by vomiting and/or diarrhea. It is very likely that the puppy could have this disease but there are many other possible problems, such as parasite infestation, food borne infection, intussusception, other viral illnesses, etc. It is very important to have puppies examined when they have a combination of vomiting or diarrhea and depression. If parvovirus is present it is important to treat it promptly and aggressively. Please take the puppy to your vet.

The risk to the other dogs is very low. In adult dogs parvovirus infection is often inapparent and the duration of immunity from vaccinations appears to be much longer than one year if the vaccine is administered when the dog is past the period of maternal antibody influence (greater than 20 to 24 weeks of age when vaccinated).

Mike Richards, DVM

Parvo in vaccinated dog

Q: My 13 month old AKC beagles had 5 vaccinations for parvo and last week contracted the virus anyway. Have you heard of a genetic problem that may have affected the efficacy of the vaccines? If they live are they facing any nuerological, cardiovascular, or other major complications? Thank you for your time. BAE

A: Doug- There are a number of possible problems that could lead to the situation you describe. Some of them are covered below.

The diagnosis could be wrong. This would be my first guess in a 13 month old dog in which one of the parvovirus vaccinations was given after 4 months of age as long as some combination of the problems below did not seem to be present as well.

A few dogs are very difficult to vaccinate for parvovirus because they get very high levels of maternal immunity, which interferes with vaccination. Using vaccines available prior to this year, about 95% of dogs are successfully protected at 16 weeks of age if the vaccine is administered properly. Most of the remaining 5% can be successfully vaccinated by 20 weeks of age. Using the new vaccines on the market currently, most puppies can be protected by 12 weeks of age and virtually all of them by 16 weeks of age.

Vaccinations given closer than 2 weeks apart can interfere with each other, reducing the immune response. Since there isn't much leeway when giving the vaccines at 2 week intervals it is better to stick to 3 week intervals, in my personal opinion. Many breeders and some veterinarians recommend vaccination every 2 weeks or even closer together. If this sort of vaccination schedule was followed the vaccine may be ineffective.

Some people refer to "nosode" vaccinations. If this was done with your puppy the odds are very very high that it didn't work. Nosodes are not an effective vaccination technique.

Your dog may have an incompetent immune system. This can happen because it never developed properly or because of an external stress such as another illness, a toxin, etc. This is actually pretty unlikely but it can occur.

Beagles do seem to be particularly sensitive to parvovirus in our practice area. I am not sure if there is an inherited immune defect or not leading to this situation. It is just my clinical impression -- I could be wrong, too.

Hope this helps.

Mike Richards, DVM

Canine parvovirus - how is it transmitted

Q: I would like to know where this virus comes from. Who or what animal is the carrier. I've always heard that CATS are the carrier. Can you please let me know. I have cats in the area. thank you

A: Rhonda- Canine parvovirus is carried by dogs. Adult dogs may be infected carriers without showing any clinical signs. Dogs with the typical diarrhea that parvovirus causes shed the virus as well. It can last a long time in the environment, perhaps as long as 9 months or so.

There is a parvovirus of cats, the panleukopenia virus. Researchers seem to think that this virus may have mutated to become canine parvovirus. This is not a confirmed theory but there is some supporting evidence for this. Perhaps this is the source of the confusion over how it is transmitted.

Mike Richards, DVM

Parvo - getting rid of the virus

Q: Hello, Just this week, I lost a 5 mo. old Boxer pup to Parvo. I have a 4 year old Beagle in the house as well. He has had his proper shots and recieved a booster as soon as the pup was diagnosed. The Beagle, so far, shows no symptoms of the disease. (Let's hope it stays that way!) The Beagle was removed from the household until I had bleached the yard 3 times in a 50/50 solution of bleach/water. The lawn has been cut after each bleaching. The house, floors, furniture and my bedding have been treated the same. All the bedding, toys etc of both the pup and Beagle have been dicarded and the Beagle has been given brand new items to replace them. I have brought the Beagle home now. The back yard was the area where the pup "left" all her body fluids etc. How long should I wait before - 1). I let the Beagle have access to the backyard? - 2) I can consider bringing in another Dog into the household, and would a Pup be out of the question? Note that neither animal had been out of the yard. Thanx!

A: It is very very unlikely that your Beagle will develop clinical symptoms of parvovirus. Older dogs, even if infected, often will not develop observable disease symptoms from parvovirus. Since your dog was vaccinated there is very little worry that he will have problems.

Parvovirus can live a long time in the environment. This makes it harder to advise you concerning getting a new puppy. It is possible that parvovirus can live several months (I have seen references to as long as 5 or 6 months) in the environment. You have taken good steps to reduce the risk but there would be some risk to a new puppy, especially in the next two to three months.

I would be hesitant to get a new puppy for awhile if it is less than 20 weeks of age. If it is over that age and has been vaccinated at 16 and 20 weeks of age for parvovirus, the odds are very very good that the vaccine will have protected the new puppy by then.

Mike Richards, DVM


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...