Dr. Lila Miller, D.V.M., Sr. Director, Animal Sciences and Vet Advisor, ASPCA
Canine Parvovirus is a highly contagious viral disease that is one of the most common causes of diarrhea in dogs under 6 months of age. It first appeared in the late 1970s, and is now one of the most common serious dog disease problems encountered in animal shelters, displacing distemper for that distinction. It is reported in coyotes, foxes, and wolves and probably affects most, if not all, members of the canine family. Puppies are the most susceptible, especially if they have roundworms or other internal intestinal parasites, protozoa (such as Coccidia) or bacteria. Despite aggressive therapy, parvo may have a high fatality rate. On the other hand, many adult dogs that become infected never actually show clinical signs of disease. Rottweilers, Dobermans, Pit Bulls, German shepherds and Labrador retrievers seem to be at higher risk for the disease.
The parvovirus is very stable in the environment, rendering it very resistant to most disinfectants. It can persist in organic material in the environment for over one year.
Another member of this virus family is responsible for causing panleukopenia, otherwise known as distemper, in cats. (This feline parvovirus was around before the strain that affects dogs appeared. In fact, the first vaccination efforts to control parvo were made using feline distemper vaccines.) Different strains of parvovirus have appeared over the years, and the newer strains are capable of infecting cats and of spreading even more effectively in susceptible dogs.
Fortunately for shelters, regular household bleach (sodium hypochlorite) is one of the most inexpensive means of neutralizing the virus. It should be diluted 1 part bleach to 32 parts water to make it safe to use around animals yet still be effective. If bleach is not used, the disinfectant being used must be tested and labeled as parvocidal. (Unfortunately, many products that are labeled as parvocidal are not very effective.) The bleach must remain in contact with the surface to be disinfected for at least 5-10 minutes to be effective.
Parvo disease is spread from dog to dog mainly through exposure to contaminated feces. It is also spread through contact with fomites (contaminated objects). Common fomites include hands, instruments, clothing, food and water dishes toys and bedding. Insects and rodents can also provide a means for disease spread.. The virus can be carried on the dog’s hair coat as well.
The incubation period, or period between contact with the virus and the appearance of symptoms can range from 4-14 days. A serious problem for shelters is that apparently healthy animals with parvo may be adopted out while they are incubating the disease, and they become ill a few days later in their new home, causing much heartache for the shelter staff and the new owners.
Parvovirus can be shed in the feces 4-5 days after exposure to the virus, which is generally before signs of illness appear. The virus will also be shed in the feces for 2-3 weeks after an animal has recovered from the disease. Incoming puppies should be quarantined for several days to watch for the onset of signs, and recovered animals should be isolated for 3 weeks before rejoining the general population.
Parvovirus affects the digestive system and the heart. The signs can vary widely. There can be subclinical infection with no signs or mild signs of lethargy and appetite loss that only lasts for 1 or 2 days. The most common clinical symptoms that shelters see are varying degrees of vomiting, diarrhea which is foul smelling and can be very bloody, loss of appetite, fever, weakness, depression and dehydration. The heart symptoms can result in sudden death without other signs, sudden death weeks to months after apparent recovery from other parvo signs, or sudden onset of symptoms of congestive heart failure in puppies under 6 months of age.
The disease is commonly diagnosed by an evaluation of the clinical signs accompanied by clinical laboratory tests. It must be remembered, however, that not all cases of bloody diarrhea and vomiting are caused by parvovirus.
There are Elisa fecal test kits available that can be used in the shelter to test for parvo. However, parvo testing can present problems if the limitations of the tests are not understood. False negative results can be obtained because parvovirus is shed for a few days only. Test results are most accurate if taken the first few days after infection, or within 5 days after clinical signs appear. False positive results are often a result of recent vaccination with a modified live vaccine (within 5-12 days of vaccination).
Parvovirus can have a fairly high mortality rate in puppies despite early or aggressive therapy. There is no specific cure, so treatment consists of providing supportive care so the body can produce enough antibodies of its own to neutralize the virus. Supportive care consists of antibiotics to fight off secondary bacterial infections, fluids to correct the dehydration and control of the vomiting and diarrhea. Food should be withheld and not given until the vomiting has stopped for at least 24 hours, and water should be offered in small amounts only, as it may sometimes induce vomiting. Puppies that survive for 3-4 days generally have a good chance of making a full recovery within a week.