Parvo

"Recently TOBY had exposures to another puppy infected with the Parvo...that started a spate of tests and monitoring to ascertain that TOBY has not been infected...It has been a week or so and fortunately till now he is ever more active and does not show any symptoms of the said disease... With this incident TOBY feels it is a good idea to reveal the myths and facts behind this deadly virus....The PARVO" (AJ)

CANINE PARVOVIRUS: WHAT IS IT?
Parvoviruses are a large group; 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 (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 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.

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 page is to clear up these misconceptions and provide the public with an accurate information source.

How is parvo spread?

CPV-2 is known to survive on inanimate objects - such as clothing, food pans, and cage floors - for 5 months and longer in the right conditions. Insects and rodents may also serve as vectors playing an important role in the transmission of the disease. All parvoviruses are extremely stable and are resistant to adverse environmental influences such as low pH and high heat. Exposure to ultraviolet light, sodium hypochlorite (household bleach), and dimethyl benzyl ammonium chloride (Drs. Foster and Smith Disinfectant Cleaners) can inactivate parvovirus. All of these products can be impaired by organic matter and need to have adequate exposure time and proper concentrations to work effectively. The normal incubation period in the animal is from 7-14 days after initial exposure. Active excretion of the virus in the feces can begin the third day after exposure, often before clinical signs appear, and may last for one to two weeks after the onset of the disease.

Symptoms

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 are seen in dogs less than 6 months of age, with the most severe cases seen in puppies younger than 12 weeks of age. There are also significant differences in response to CPV-2 infections and vaccines among different breeds of dogs, with Rottweilers, Doberman Pinschers, and Labrador Retrievers being more susceptible than other breeds.

The most common form of the disease is the intestinal form known as enteritis. CPV-2 enteritis is characterized by vomiting (often severe), diarrhea, dehydration, dark or bloody feces, and in severe cases, fever and lowered white blood cell counts. Acute CPV-2 enteritis can be seen in dogs of any breed, sex, or age. The disease 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 the disease and slow recovery.

Diagnosis

Not all cases of bloody diarrhea with or without vomiting are caused by Parvovirus and many sick puppies are misdiagnosed as having 'Parvo.' The only way to know if a dog has Parvovirus is through a positive diagnostic test. In addition to the more time consuming and expensive traditional testing of the blood for titers, a newer and simpler test of the fecal matter with an enzyme-linked immunosorbent assay antigen test (ELISA) are also available through most veterinary clinics. Testing of all suspect cases of Parvo is the only way to correctly diagnose and treat this disease.

Treatment

The treatment of Parvovirus is fairly straightforward and directed at supportive therapy. Replacing fluids lost through vomiting and diarrhea is probably the single most important treatment. Intravenous administration of a balanced electrolyte solution is preferred, but in less severe cases, subcutaneous or oral fluids may be used. Antibiotic therapy is usually given to help control secondary bacterial infections. In cases of severe vomiting, drugs to slow the vomiting may also be used. After the intestinal symptoms begin to subside, a broad spectrum de-worming agent is often used. Restricting the food during periods of vomiting is also necessary. Undertaking the treatment of affected dogs and puppies without professional veterinary care is very difficult. Even with the best available care, the mortality of severely infected animals is high. Without the correct amount of properly balanced intravenous fluids, the chance of recovery in a severely stricken animal is very small.

Immunity and vaccination

If a puppy recovers from CPV-2 infection, it is immune to reinfection for probably at least twenty months and possibly for life. In addition, after recovery, the virus is not shed in the feces. There are many commercially prepared attenuated (modified) live CPV-2 vaccines available. Although some people have expressed concern about the possibility of attenuated live vaccines reverting to a virulent strain after being given and then causing disease, 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 canine 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 colostral transfer of maternal antibody within those first 24 hours. High levels of maternal antibodies present in the puppies' 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 a couple weeks in which the maternal antibodies are too low to provide protection against the disease, but too high to allow the vaccine to work. This period is called the window of susceptibility. This is the time when despite being vaccinated, a puppy can still contract parvovirus. The length and timing of the window of susceptibility is different in every litter.

A study done in 1985 in a cross section of different puppies showed, that the age at which they were able to respond to a vaccine and develop protection covered a wide period 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.

There is a newer Type 2 strain of vaccine known as a high titer, low passage vaccine. When using this vaccine, the percentages of puppies immunized are much higher at an earlier age. Some early studies are claiming 90% of the puppies are protected at 9 weeks of age and almost 98% protected at 12 weeks when this new Type 2 parvo vaccine is used.

When we examine all of the information about maternal derived antibodies, windows of susceptibility, throw in 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 disease. Drs. Foster and Smith recommend a protocol that will help protect the widest range of dogs. We realize that with our protocol, we will be vaccinating some dogs that are not capable of responding and we will be revaccinating some dogs that have already responded and developed a high titer. But without doing an individual test on each puppy, it is impossible to determine where the puppy is in its immune status. We also realize due to the window of susceptibility, some litters will contract parvovirus despite being vaccinated. By using quality vaccines and an aggressive vaccination protocol, we can make this window of susceptibility as small as possible.

Conclusion

In summary, parvovirus is a very common problem that is a huge killer of puppies. Due to 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 the disease. Modified live vaccines are safe and effective, but despite the best vaccination protocol, all puppies will have a window of susceptibility of at least several days where they will be at risk. Using the newer high titer vaccines may shorten the window of susceptibility on many puppies. Prompt treatment by a veterinarian will increase survivability in infected puppies and working with your veterinarian on a vaccination program that is best for your puppy is important. As new information on this disease and vaccines becomes available, we will continue to update this article in hopes of keeping you as informed on Parvo as possible.