Parvoviruses are a large group; almost every mammal species (including humans) seems to have its own parvovirus. Fortunately, each virus is specific for which animal species it can infect (i.e. the pig parvovirus will not infect people, the canine parvovirus will not infect cats, etc.) The canine parvovirus will affect most members of the dog family (wolves, coyotes, foxes etc.).
Parvoviruses are smaller than most viruses and consist of a protein coat (a capsid) and a single strand of DNA inside. It is hard to believe that such a simply constructed organism could be so deadly; however, this virus has proved especially effective at infecting rapidly dividing host cells such as intestinal cells, bone marrow cells, cells of the lymph system, and fetal cells. Parvoviruses are not enveloped in fat the way many other viruses are. This makes parvoviruses especially hardy 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, and it 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.
Over thirty years have passed since then. The most common 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. It is also worth mentioning the new particularly virulent strain of parvovirus: CPV-2c, which is rapidly becoming the second most common form of canine parvovirus. CPV-2c was discovered in the year 2000 and is able to infect cats. Cats vaccinated against feline distemper can be considered protected. Currently available vaccines cover all variants of canine parvo including CPV-2c as do all the commercially available diagnostic test kits.
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.
Treatment for parvoviral infection centers on supportive care. 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 antiviral drugs and must rely on the patient’s immune system for cure.
BE PREPARED FOR A 5 to 7 DAY HOSPITAL STAY AND SUBSTANTIAL EXPENSE.
INTENSIVE CARE IS NEEDED TO TREAT THIS INFECTION.
There are certain basic treatment principles that can be viewed as “must haves” in addressing the parvo puppy.
Beyond these basics are some added pluses that may or may not contribute to the chance for survival. In order to achieve the usual survival rate of approximately 75-80%, 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.
One of the ways parvo can kill is via the metabolic derangements that occur with extreme 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 small puppy.
The second way parvo kills is through bacterial invasion of the circulatory system (sepsis). The intestine is normally full of bacteria and when the parvovirus ulcerates the intestine there is little to prevent the bacteria from marching easily into the bloodstream. With the GI tract 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 that may be selected. Some antibiotics you may see in use include:
- Injectable metronidazole
Some veterinarians prefer Cefazolin as a basic choice. For more information on this drug you may wish to our article on its sister drug Cephalexin.
Cefovecin is a single injection that lasts 2 weeks. This product has not been adequately tested in puppies under age 16 weeks but may find a place in the treatment of older puppies.
Control of Nausea
Patient comfort is an 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 several 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 strong nausea control medication that lasts 6 to 8 hours per injection and has the added benefit of a drowsiness side effect (so patients can sleep through most of this uncomfortable time).
Ondansetron and dolasetron: These injectables are especially strong anti-nausea medications. In the past, expense has made these medications uncommon but recent generics have made them readily available. Ondansetron is typically given two to three times daily while dolasetron is given only once daily.
Maropitant (brand name: Cerenia®): This powerful anti-nausea has not been adequately tested in puppies under 16 weeks of age. For older puppies, this should be an excellent choice to improve patient comfort. It is given once daily.
The vomiting typical of parvo infection is not only uncomfortable but can ulcerate the esophagus. The disease itself ulcerates the stomach and small intestine. Medications called gastroprotectants help heal ulcers and help minimize their formation. These medications include the injectable antacids (cimetidine, ranitidine, or famotidine) as well as sucralfate, which forms webbing over ulcers to facilitate healing.
The following tests are helpful in adjusting parvovirus treatment:
- Fecal flotation to rule out worms/internal parasites
The last thing these patients need is a parasite burden contributing to their nausea and diarrhea. Since parvo victims are puppies and puppies are high risk for parasitism, it is important to test for worms and microbes that can contribute to the GI upset and eliminate them.
2) 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. The white blood cell count bottoms out at the height of the viral infection and recovers as the patient’s immune system gains the upper hand.
3) Urine specific gravity/Azostix
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 Azostix measures of protein metabolites, which build up in the blood stream, should be at normal levels.
4) 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.
5) Total blood protein
Protein depletion is common when there is heavy diarrhea. If blood proteins drop too low, certain IV fluids or even plasma transfusions are needed to prevent massive life-threatening edema.
Extra Treatment that May Help
While this particular addition to the parvo treatment plan has not universally caught on everywhere, news of its efficacy has spread far and wide. This oral medication is typically given for 5 days starting as soon as the diagnosis is made. It interferes with the reproduction of the parvovirus so that the patient’s immune system essentially has fewer enemy soldiers to combat. This medication is helpful in th treatment of parvo patients plus it can prevent development of the disease when given to exposed puppies. The key is to begin this treatment before the virus has had a chance to maximize its numbers; if treatment is started later in the infection, there may be so many viral particles that little benefit can be realized.
Plasma is the protein-rich fluid that remains when the red blood cells are removed from a sample of blood. These proteins may include antibodies against the parvovirus, albumin to help expand the patient’s blood volume, as well as other healing proteins. Plasma can be obtained from donor dogs in the hospital or can be purchased from animal blood banks.
Cefoxitin (an 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 gentamicin or amikacin, and without the cartilage side effects of Baytril.
This product represents anti-serum (antibodies extracted from horses) that 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.
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). The usual medication is flunixin meglumine (Banamine®).
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. In other words, Neupogen helps the white cell count recover. 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 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.
The Parvo Puppy Goes Home – What you Need to Know
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 been prescribed.
Your puppy is recovering from some extensive damage to the 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 to 5 days at home, and your puppy should be active and have a normal attitude. If the diarrhea persists, if vomiting occurs, or if your puppy seems depressed, please contact your veterinarian 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 therapeutic 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.
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, she should not be allowed in public areas until the vaccination series is fully completed.
Humans are not susceptible to canine parvovirus infection though some strains can be contagious to cats. 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 any time the ground is frozen does not count in this 7-month period.)
Your puppy may be bathed any time as long as you do not allow her to get cold or chilled after the bath. Bathing will reduce the amount of virus left on her fur and will help reduce contagion.
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 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).
Date Published: 1/1/2001
Date Reviewed/Revised: 10/12/2011
Copyright 2011 – 2013 by the Veterinary Information Network, Inc. All rights reserved.