The first signs of CPV infection are depression, loss of appetite, vomiting, and diarrhea. Fever may or may not be present. These signs will most often appear 5-7 days after the dog is exposed to the virus. At the onset of illness, feces will generally be light gray or yellow-gray. Sometimes, the first sign will be fluid feces with blood.
Dehydration can occur rapidly due to vomiting and diarrhea.
Some dogs may vomit repeatedly and have projectile, bloody diarrhea until they die. Others may have loose feces and recover without complications. Most deaths occur within 48-72 hours following the onset of clinical signs. This syndrome occurs without concurrent diarrhea because the virus multiplies rapidly in muscle cells of the growing heart. Pups with parvoviral myocarditis may act depressed and stop suckling shortly before they collapse.