A dog cannot contract canine parvovirus more than once. Once a dog recovers fully from the parvovirus, it is immune from it for the rest of its life.
Canine parvovirus, often called parvo, is an extremely dangerous and potentially deadly illness that attacks the bone marrow and intestines of affected dogs. Because the virus can live for many months outside the body, it is easy for unvaccinated dogs, especially puppies, to catch. Parvovirus makes itself known through diarrhea and vomiting. It weakens the dog's immune system severely, causing extreme weakness and often death. All dogs should be vaccinated against parvo, and puppies suffering from severe diarrhea should be taken to the veterinarian immediately for testing.