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Understanding Parvo In Dogs

from: Kyle Besser

Canine parvovirus (CPV) in dogs is currently the most common infectious disorder of dogs in the United States. Current vaccinations have helped to control the spread of Canine parvovirus (CPV) in dogs but despite being vaccinated, some dogs still contract and die from parvo. There is much that is not known about the parvovirus or the best way to control Canine parvovirus (CPV) in dogs. Misinformation about Canine parvovirus (CPV) in dogs, its spread, and vaccination is widespread.

Prior to 1980, most canine parvovirus that caused disease was Type 2 (CPV-2). After 1980, CPV-2 was replaced by CPV-2a and became more common. In 1986, another variation called CPV-2b appeared. In the past few years, a new strain, CPV-2c has been detected. Today, CPV-2b has largely replaced the previous strains as the most common parvovirus causing disease in the dog. There is currently some discussion that there may be other strains of canine parvovirus that are beginning to emerge and have yet to be formally identified.

With a better understanding of the canine parvovirus disease, dog owners will be able to make better health decisions for their dogs that will help prevent and reduce the spread of this disease.

Parvo, as the disease is commonly called, is a highly contagious disease characterized by diarrhea that is often bloody. The parvovirus is spread through contact with feces containing the virus. The canine parvovirus is known to survive on inanimate objects, such as clothing, food containers, and cage floors for 5 months and longer under the right conditions. Insects and rodents may also play an important role in the transmission of the disease. This means any fecal material or vomit needs to be removed with a detergent and then a bleach solution should be used. The bleach solution should be used on bedding, dishes, kennel floors and other materials that may be contaminated.

The normal incubation period from exposure to the dog parvovirus to the time when signs of parvo disease appear is from 7 to 14 days. Active excretion of the virus in the feces can begin the third day after exposure, which is often before clinical signs appear, and may last for 1 to 2 weeks after the onset of the disease.

Symptoms of parvovirus infection:

There is a broad range in the severity of symptoms shown by dogs that are infected with parvovirus. Many adult dogs exposed to the virus show very few, if any, symptoms. The majority of cases of parvo are seen in dogs less than 6 months of age. The most severe cases are seen in puppies younger than 12 weeks of age.

There are also significant differences in response to parvovirus infections and vaccines among different breeds of dogs. Doberman Pinschers, Labrador Retrievers and Rottweilers are more susceptible than other breeds.

The most common form of the dog parvovirus disease is the intestinal form known as enteritis. Parvovirus enteritis is characterized by vomiting (often severe), diarrhea, dehydration, dark or bloody feces. In severe cases of Parvovirus enteritis, there can be fever and lowered white blood cell counts. A less common form of the disease causes myocarditis (inflammation of the heart).

Acute parvovirus enteritis can be seen in dogs of any breed, sex, or age. Acute parvovirus enteritis will progress very rapidly and death can occur as early as two days after the onset of the disease. The presence of gram negative bacteria, parasites, or other viruses can worsen the severity of acute parvovirus enteritis and slow recovery.

Diagnosis of parvovirus:

The only way to know if a dog has parvovirus is through a positive diagnostic test. Not all cases of bloody diarrhea with or without vomiting are caused by parvovirus, and many sick puppies are misdiagnosed as having parvo.

In addition to the more time consuming and expensive traditional testing of the blood for titers, a simpler test of the feces with an enzyme-linked immunosorbent assay antigen test (ELISA), commonly called the CITE test, is also available through most veterinary clinics. Testing of all suspected cases of parvo is the only way to correctly diagnose and treat parvo. A complete physical exam and additional laboratory tests such as a CBC and chemistry panel help to determine the severity of the parvo disease.

Treatment of parvovirus:

The treatment of parvovirus in dogs is fairly straightforward and directed at supportive therapy. Replacing fluids lost through vomiting and diarrhea is probably the single most important part of the treatment of parvovirus in dogs. Intravenous administration of a balanced electrolyte solution is the preferred treatment of parvovirus in dogs. In less severe cases, subcutaneous or oral fluids may be used. In severe cases, blood transfusions may be necessary.

Antibiotic therapy is usually given to help control secondary bacterial infections. In dogs with severe symptoms of parvovirus, antiserum against endotoxins may be given. Corticosteroids may be given if the animal is in shock. In cases of severe vomiting, drugs to slow the vomiting may be used. After the intestinal symptoms of parvovirus begin to subside, a broad spectrum deworming agent is often used. Restricting the food during periods of vomiting is also necessary and parenternal nutrition (providing nutrients intravenously) may be necessary.

Undertaking the treatment of parvovirus in dogs and puppies without professional veterinary care is very difficult. Even with the best available care, the mortality rate of severely infected dogs and puppies is high. Without the correct amount of properly balanced intravenous fluids, the chance of recovery in severely infected dogs and puppies is very small.

All parvoviruses are extremely stable and are resistant to adverse environmental influences such as low pH and high heat. Exposure to ultraviolet light and sodium hypochlorite (a 1:32 dilution of household bleach - � cup bleach to 1 gallon of water) can inactivate parvovirus. The bleach solution can be impaired by organic matter and needs to have adequate exposure time and proper concentrations to work effectively and to inactivate the parvovirus.

If a puppy recovers from dog parvovirus infection, the puppy is immune to reinfection for probably at least 20 months, possibly for life. After recovery the parvovirus is not passed in the feces.

Immunity and vaccination for parvovirus:

There are many commercially prepared attenuated (modified) live CPV-2 vaccines available. Some have expressed concern about the possibility of modified live vaccines reverting to a virulent strain after being given and then causing disease, but studies have repeatedly shown that this does not occur. Commercially prepared vaccines are safe and do not cause disease.

The primary cause of failure of canine parvovirus vaccines is an interfering level of maternal antibody against the parvovirus. Maternal antibodies are the antibodies present in the mother's milk during the first 24 hours after the puppy's birth. The age at which puppies can effectively be immunized is proportional to the titer of the mother and the effectiveness of transfer of maternal antibodies within those first 24 hours. High levels of maternal antibodies present in the puppy's bloodstream will block the effectiveness of a vaccine.

When the maternal antibodies drop to a low enough level in the puppy, immunization by a commercial vaccine will work. The complicating factor is that there is a period of time from several days to several weeks in which the maternal antibodies are too low to provide protection against the parvovirus, but too high to allow the vaccine to work. This period is called the window of susceptibility. During this window of susceptibility, despite being vaccinated, a puppy can still contract parvovirus. The length and timing of the window of susceptibility is different in every puppy in every litter.

In one study of a cross section of different puppies, the age at which the puppies were able to respond to a vaccine and develop protection covered a wide range of time. At six weeks of age, 25% of the puppies could be immunized. At 9 weeks of age, 40% of the puppies were able to respond to the vaccine. The number increased to 60% by 16 weeks, and by 18 weeks of age, 95% of the puppies could be immunized.

When we examine all of the information about maternal derived antibodies, windows of susceptibility, breed susceptibilities, the possibility of unidentified strains, and the effectiveness of different vaccines, we begin to see why there are so many different vaccination protocols and why some vaccinated animals still develop the parvo dog disease.

Vaccination protocols have been developed that will help protect the widest range of dogs. By using these vaccination protocols, it is understood that some puppies will be vaccinated that are not capable of responding and some puppies will be revaccinated that have already responded and developed a high titer. Without doing an individual test on each puppy, it is impossible to determine where the puppy is in its immune status.

Due to the window of susceptibility, some litters will contract parvovirus despite being vaccinated. By using quality vaccines and an aggressive vaccination protocol, this window of susceptibility can be kept as small as possible. The generally recommended protocol is to vaccinate puppies against parvovirus beginning at 6 to 8 weeks of age and revaccinating every 3 weeks until the puppy is 16 to 20 weeks of age. A booster is given at one year of age and every 1 to 3 years thereafter.

Parvo dog disease is a very common problem that is a huge killer of puppies. Because of its ability to be transmitted through hands, clothes, and most likely rodents and insects, it is virtually impossible to have a kennel that will not eventually be exposed to Parvo dog disease. Modified live vaccines are safe and effective, but despite the best vaccination protocol, all puppies have a window of susceptibility of at least several days when they will be at risk for the parvovirus.

The newer CPV-2c strain presents new challenges since it is less detectable in laboratory tests and current vaccines may not be as effective in providing protection against it. Prompt treatment by a veterinarian will increase the survivability of parvo infected puppies. Working with your veterinarian on a vaccination program that is best for your puppy is important.