Parvo in puppies is caused by the canine parvovirus. This virus is highly contagious and spreads through direct contact with an infected dog or by indirect contact with a contaminated object. Your puppy is exposed to the parvovirus every time he sniffs, licks, or consumes infected feces. Parvo is not always fatal, but when it does result in death, it is as a result of either dehydration and/or shock, along with the effects of septic toxins produced by the intestinal bacteria roaming throughout the bloodstream.