Canine parvovirus is carried by dogs. Adult dogs may be infected carriers without showing any clinical signs. Dogs with the typical diarrhea that parvovirus causes shed the virus as well. It can last a long time in the environment, perhaps as long as 9 months or so.
There is a parvovirus of cats, the panleukopenia virus. Researchers seem to think that this virus may have mutated to become canine parvovirus. This is not a confirmed theory but there is some supporting evidence for this