Dogs are at risk of enteritis (intestinal disease) caused by two common viruses, canine parvovirus and canine coronavirus. Canine parvovirus enteritis is generally considered to be more severe than coronavirus enteritis. However, parvovirus enteritis may be more serious if coronavirus is also present. Diarrhea and vomiting caused by these viruses can range from mild to severe, and are accompanied by depression and loss of appetite. Unvaccinated puppies and young dogs are most commonly affected because they usually have not been previously exposed or vaccinated and are susceptible to infection. Viral enteritis is easily spread because of the large volume of virus in the feces, which contaminates the environment and is readily spread from one animal to another. Severe cases of viral enteritis can be fatal due to dehydration and loss of appetite. Puppies are at greatest risk of death because of their limited body reserves.