Hanson-Meekins Animal Hospital

PARVOVIRUS

Almost every mammal species (including humans) seems to have its own parvovirus. Fortunately, each virus is pretty specific about what animals 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, including wolves, coyotes, and foxes.  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. 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", though there is some controversy regarding what the parent parvovirus actually was. 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.

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. Over thirty years have passed since then. The most common form of the virus is called CPV-2b. It is also worth mentioning the new particularly virulent strain of parvovirus: CPV-2c was discovered in the year 2000 and is able to infect cats. Cats vaccinated against feline distemper can be considered protected.

WHERE DOES VIRUS COME FROM?

Remember that this virus has been around since the 1970’s, and is very hard to disinfect away. It is shed in extremely large numbers by infected dogs, and can persist in organic material in the environment for over one year. The virus is shed in the stool for the first two weeks or less after the initial infection 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 are infected but 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.

PARVOVIRUS: HOW DOGS GET INFECTED AND WHAT HAPPENS TO THEM

The incubation period, or period between contact with the virus and the appearance of symptoms, is usually 4-6 days. 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.) Parvo disease is spread from dog to dog mainly through exposure to contaminated feces. It is also spread through contact with contaminated objects, i.e. hands, instruments, clothing, food and water dishes, toys and bedding. The virus can remain on a dog's hair coat and serve as a means of transmission long after recovery from clinical disease.

DIAGNOSIS OF PARVOVIRUS

 A puppy with a bloody diarrhea could have a parasite problem, a virus other than parvovirus, a stress colitis, an intestinal foreign body, or may simply 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 ELISA test has become the most common test for parvovirus in puppies.  The parvo ELISA test is also a kit and is performed in the vet’s office in about 15 minutes or less. 

TREATMENT

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.

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.

ANTIBIOTICS: 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.

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. The vomiting typical of parvo infection is not only uncomfortable but can ulcerate the esophagus. The disease itself ulcerates the stomach and small intestine.

 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 can be given under the skin at home as can injectable medicines.

CARING FOR THE RECOVERED DOG

 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 on his food 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.

Other Pets Healthy Adult dogs that have been vaccinated are not susceptible, but puppies, or dogs with weak immune systems, 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 over 12 months before the virus is eliminated from soil. 

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 up to 3 years 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.

VACCINATIONS OPTIONS / PREVENTIONS

Maternal Antibody: Our biggest obstacle

Puppies obtain their immunity from their mother’s first milk, the colostrum, on the first day of life. This special milk contains the mother’s antibodies against parvovirus and until these antibodies wane to ineffective levels, they will protect the puppy.  The problem is that they will also inactivate vaccine.

Vaccine is a solution of inactivated virus, either live and weakened (“attenuated” or “modified”) or killed. This virus is injected into the puppy. If there is still adequate maternal antibody present, this vaccine virus will be destroyed just as if it were a real infection. There will be a period of about a week when there is not enough maternal antibody to protect the puppy but too much to allow a vaccine to work. (This period is called the “window of vulnerability.”) Then after this, vaccine can be effective.  The next problem is the age at which vaccine can be effective is different for each individual puppy. To get around this, we vaccinate puppies in a series, giving a vaccine every 4 weeks until age 16 weeks. 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.  By age 16 weeks, we can be certain that maternal antibodies have waned and the vaccine should be effective. 

After a puppy is born, maternal antibody levels drop by half approximately every 10 days.
Puppies that were born first or were more aggressive at nursing on the first day will get more maternal antibody than their littermates.

Mother dogs vaccinated at approximately the time of breeding will have the highest antibody levels to pass on to their puppies.

*** REMEMBER, the more maternal antibody a puppy has, the less likely a vaccine is to work.

It is commonly held that puppies need a certain number of vaccines for protection to be achieved (usually either 3 or 4 is the “magic” number). The number of vaccines given has nothing to do with protection. In order for protection to be achieved, vaccine must be given when it can penetrate maternal antibody.

VACCINATING ADULT DOGS

Classically, parvovirus vaccine has been administered annually to all dogs. Vaccine against canine parvovirus has been included in the distemper combination vaccine (the “DHLPP”, “6 in one” etc.)