This virus barely existed before the 1970s, but in no time became a major cause of canine death. Currently, it is primarily a cause of severe illness and death for puppies and adolescent dogs; fortunately, vaccinations are an effective route of prevention if performed on the proper schedule. 

Parvoviruses are a large group; almost every mammal species, including humans, seems to have its own parvovirus. Fortunately, each virus is specific, at least for the most part, for which animal species it can infect (i.e. the pig parvovirus will not infect people, the canine parvovirus will not infect pigs, etc.) For this reason, when a dog or puppy in the family has a parvo infection, the human family is safe. That said, the canine parvovirus is not as specific as some of the other parvoviruses. It will affect most members of the dog family (wolves, coyotes, foxes, etc.) and there is a new mutation that can affect domestic cats (see below).

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 by 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 hardy in the environment and difficult to disinfect away.

Parvovirus-canine

Canine parvovirus. Reprinted with permission by Jean-Yves Sgro. © 1994 JY. Sgro UW-Madison

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 or "the minute virus of canines," 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 though there is some controversy regarding what the parent parvovirus actually was). 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 in every environment unless some form of 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, and it seemed to be even more aggressive. The vaccine was at a premium and many veterinarians had to make do with the feline distemper vaccine as it was the closest related vaccine available while the manufacturers struggled to supply the nation with true parvo vaccines.

Over 40 years have passed since then. The most common 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. It is also worth mentioning the new particularly virulent strain of parvovirus: CPV-2c is rapidly becoming the second most common form of canine parvovirus. CPV-2c was discovered in 2000 and is able to infect cats. Cats vaccinated against feline distemper can be considered protected. Going back to dogs, currently available vaccines for dogs cover all variants of canine including CPV-2c as do all the commercially available diagnostic test kits.

For more specific information about canine parvovirus-2c, see the following from the American Veterinary Medical Association.

Learn more about the virus at Baker Institute for Animal Health, part of the Cornell University College of Veterinary Medicine.

Parvoviral infection has become a disease almost exclusively in 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 percent. Still, there are many myths and misunderstandings about this virus, how it is spread, and how to prevent it. The purpose of this article series is to clear up these misconceptions and provide the public with an accurate information source.