 because these dogs don't have natural protection to it. This virus takes advantage of their gastrointestinal tract, so it destroys their bone marrow and really destroys their GI tract by giving them an inability to hold in their fluids, so they get terrible vomiting, terrible diarrhea, they get dehydrated, and then they can get bacteria that enters their bloodstream as a result. Really, really devastating, and if left untreated, it's almost always fatal.