As shown in its name, parvovirus is a viral illness. Parvovirus is predominantly a disease of young puppies between 6 weeks and 6 months of age. An approximate of 80% affected puppies die out of the said virus. When proper treatment is given, an estimated 85% of the affected puppies will live.
Parvovirus is highly resistant and can survive in the environment for up to 5 months. Infection generally follows exposure to infected feces. The incubation period can last from 4 to 14 days. Puppies or dogs afflicted with canine parvovirus show vomiting and diarrhea as major clinical signs. The diarrhea is usually yellow to yellow gray at first but quickly becomes blood tinged or dark red in most cases.
Prevention of parvovirus
Puppies receive protection from parvovirus in the colostrum, or first milk produced by their mothers. This protection depends whether the mother had antibodies against parvovirus and how much colostrum a puppy received in its first 24 hours of life. In some cases this protection is not conferred. This variability in maternal protection is the major reason a series of vaccinations is given to puppies. A starting date for vaccination is picked based on the puppy’s ability to respond to infection and the likely timing of exposure to the disease.
In general, the first vaccination in the puppy series is given between 6 and 8 weeks of age. Only a few puppies are capable of responding to this initial vaccine series. It is not practical to conclude in advance which puppies respond to the vaccine thus all puppies should be vaccinated. The puppies that need the protection get it and the rest do not benefit from the first vaccine. The second vaccine is preferably given at least 2 weeks later and preferably 3 to 4 weeks later. A larger percentage of puppies respond to this vaccine but not all of them. The vaccination series is continued at 3 to 4 week intervals until it is likely that all puppies can respond to vaccination have done so. The number of vaccinations in the series and the age at which the final puppy series vaccination is given will depend on the type of vaccine used, the breed of the puppy, the puppy’s lifestyle, the owner’s experiences and the veterinarian’s experiences with the disease.
Vaccines available
Several manufacturers to prevent parvovirus produce vaccines. Most of the currently available vaccines are high antigen vaccines break through maternal antibody protection earlier than the original parvovirus vaccines. These vaccines also provide protection in most puppies when given between 12 and 14 weeks of age. The older parvovirus vaccines had to be given until 16 or even 20 weeks of age to ensure maximum protection. Of the currently available vaccines still in use only the Vanguard TM series of vaccines from Pfizer Animal Health TM is the older type of vaccine (as of 2006, per “Infectious Diseases of the Dog and Cat” by Greene). There is a period of time, between 2 and 3 weeks, when the parvovirus strains found in most infections can cause disease before there is a chance for vaccinations to work. At the present time there is no way to avoid this period. More frequent vaccination is not helpful and vaccinations given closer than two weeks apart may even impair immunity. For this reason, it is best to avoid exposure to potential sites of infection, such as dog parks, dog shows and kennels until after the last vaccine in the series. It is also important to remember that the veterinarian’s office is a potential site of contamination, especially the area outside the veterinary hospital. Puppies should be walked directly to the door and should be kept away from other puppies in the waiting room that appear to be ill. Veterinary hospitals and kennels try very hard to properly clean up after incidences of diarrhea and in areas in which exposure can occur but it is hard to do this perfectly. Parvovirus is very hardy in the environment. If your house becomes contaminated by the virus clean any surfaces that can be cleaned with chlorine bleach diluted 1 oz of bleach to 32 oz of water. The disinfectant potassium peroxymonosulfate (Trifectant TM or Virkon TM) is also effective. It is extremely hard to disinfect a yard. Realistically, if your yard has been potentially contaminated with parvovirus it would probably be best not to get a new puppy and expose it to the yard for at least six months and nine months would be better. Areas of the yard that are exposed to sunlight will require less time for the virus to die than areas of the yard that are shaded, moist and sandy. At the present time there is not a disinfectant product marketed for use in yards that has been proven to be effective against parvovirus.
Immunity
If a puppy recovers from parvovirus infection, he 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. The current vaccines protect against all strains of the canine parvovirus, including the relatively new parvovirus-2c strain. Although some people have expressed concern about the possibility of modified live vaccines reverting to a virulent strain after being given and then causing disease, studies have repeatedly shown that this does not occur.
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 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 several 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 puppy in every litter.
In one study of a cross section of different puppies 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.
Vaccination protocols have been developed that will help protect the widest range of dogs. In using these protocols, we understand 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. The generally recommended protocol is to vaccinate puppies against parvovirus beginning at 6-8 weeks of age, and revaccinating every 3 weeks until the puppy is 16-20 weeks of age. A booster is given at one year of age and every 1-3 years thereafter.
In conclusion, parvovirus has become one of the most dreaded and deadly disease of puppies. Its ability to be transmitted through hands, clothes, and most likely rodents and insects makes parvovirus to be virtually impossible to have a kennel that won’t be exposed to the disease. Modified live vaccines are considered safe and effective yet remains subjected to a window of susceptibility of at least several days where puppies are at greatest risk. What’s more is that the newer CPV-2c strain presents new challenges due to its trait of less detectable in laboratory tests, also current vaccines may not be as effective in providing protection against it. Prompt treatment by a veterinarian will increase survivability in infected puppies. Always work with your vet on a vaccination program deemed best for your puppy.
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