The main reasons why dogs suffer from parvovirus are: First, improper diet. If the owner feeds the puppies milk, oily food, onions, chocolate, grapes and other foods for a long time, it will easily cause them to become infected with parvovirus; The second is catching a cold and having diarrhea. In this case, it is easy to develop secondary enteritis. In severe cases, it is very likely to be directly infected with parvovirus. The third is being infected by a dog suffering from parvovirus. Parvovirus is a very contagious disease. The resistance itself is very poor, and even small dogs can be infected through indirect contact.