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Canine Parvovirus (parvo) 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 one of the most frequent serious dog disease problems encountered in animal shelters. 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, and their clinical signs are worsened by concurrent infections with roundworms, other internal intestinal parasites, protozoa (such as Coccidia), viruses or bacteria. Adult dogs can also be affected.
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In general, if aggressive therapy is initiated early in the course of the disease, the prognosis for puppies to recover can be excellent, although fatalities do occur. However, the mortality rate for puppies in shelters can be much higher because many shelters cannot diagnose, isolate or treat the cases. As for adult dogs, many become infected but 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.
What Causes Parvovirus
Canine parvovirus is very stable in the environment and 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, more commonly known as distemper, in cats. (This feline parvovirus was present before the strain that affects dogs appeared. In fact, the first vaccination efforts to control canine parvo were made using feline panleukopenia vaccines.)
Different strains of parvovirus have evolved over the years since it was first discovered in dogs in 1978. The current strains infecting dogs in the United States are CPV-2b and CPV-2c, which also can cause illness and have been isolated from cats. In the shelter it is essential to separate dogs from cats, as cats can not only develop illness but also act as a reservoir causing further disease in dogs.
How Parvovirus Is Transmitted
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 remain on a dog's hair coat and serve as a means of transmission long after recovery from clinical disease. The incubation period, or period between exposure to the virus and the appearance of symptoms, is usually 4-6 days. Because the disease may be difficult for the shelter to detect during the incubation period, apparently healthy animals with parvo may be adopted out only to become ill a few days later in their new home, causing heartache for the shelter staff and the new owners.
It is very important to know the shedding pattern of parvovirus in order to design an effective management, diagnostic and prevention strategy. Parvovirus can be shed in the feces 3-4 days after infection with the virus, which is generally before clinical signs of illness appear. The virus will also be shed in the feces for approximately 10-14 days post-recovery from clinical signs of infection.
Clinical Signs of Parvovirus
Parvovirus affects the digestive system and the heart. The signs can vary widely:
- There can be sub-clinical infection with no signs or mild signs of lethargy and appetite loss lasting for only one or two days
- The most common clinical symptoms shelters see are varying degrees of vomiting, foul-smelling diarrhea that can be very bloody, loss of appetite, fever, weakness, depression and dehydration
- Affected puppies are also very leukopenic, meaning they have too few white blood cells
- The heart symptoms are rarely seen today and usually occur in puppies infected in utero or during the neonatal period, but they can cause 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
- Lila Miller, DVM, is Vice President of ASPCA Veterinary Outreach