CANINE PARVOVIRUS: WHAT IS IT?

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.

THE VIRUS IN THE ENVIRONMENT/DISINFECTION

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.

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.

HOW PARVO INFECTION HAPPENS

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).

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.)

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.

TREATMENT

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
• Baytril
• Ampicillin
• Gentamycin
• Amikacin
• Trimethoprim-sulfa
• Chloramphenicol

Our hospital tends to prefer Cefazolin as a basic choice. For more information on this drug you may wish to read the Pharmacy Center section on its sister drug: Cephalexin.

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.
• Chlorpromazine: a very strong nausea control medication which lasts 6-8 hours per injection and has the added benefit of a drowsiness side effect (so patients can sleep through most of this uncomfortable time). Injectable antacids (Tagamet, Zantac, or Pepcid) are often used to prevent ulceration of the esophagus of the esophagus should protracted vomited be a problem.

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.

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.

EXTRA TREATMENT WHICH MAY HELP:

CEFOXITIN (A SPECIAL ANTIBIOTIC) The best antibiotic coverage controls both gram negative and gram positive organisms, both aerobic and anaerobic organisms and does so with minimal side effects. The use of Cefoxitin (brand name Mefoxitin) does an excellent job of covering for the organisms of concern without the kidney side effects of gentamycin or amikacin and without the cartilage side effects of Baytril. Cefoxitin is especially expensive and is frequently reserved for the sickest puppies.

ONDANSETRON (BRAND NAME ZOFRAN) This medication is an especially strong anti-nauseal medication which is useful if the more common medications have failed. This medication is commonly used to control the extreme nausea experienced by people on cancer chemotherapy. While it is highly effective for parvo puppies, it is also very expensive.

SEPTI-SERUM-This product represents anti-serum (antibodies extracted from horses) which binds the toxins of any invading GI tract bacteria. The use of this product is controversial though the veterinary teaching hospital at Auburn University uses it commonly. It is usually given only one time as the equine origin of the product has potential for serious immunological reactions.

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.

ANTI-INFLAMMATORY DRUGS- There have been many studies indicating the benefits of single doses of these medications in the prevention of septic shock. Repeated doses may cause further GI ulceration (which is obviously something a parvo puppy has enough of). Our hospital favors Flunixin meglumine (brand name banamine) for this use.

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; however, in sicker puppies it may make a significant difference. It is very expensive usually adding $100-$200 to the basic treatment cost.

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 DOES NOT SURVIVE

DIAGNOSIS OF PARVOVIRUS

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.

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