Distemper is a tragic, often fatal disease of dogs and puppies. While the distemper virus is part of the typical puppy vaccine series, puppies too young for vaccination and dogs who were never vaccinated are most vulnerable. The virus typically comes along with neurological symptoms, nasal discharge, and high fevers. It also has a high mortality rate, and the rare dogs who survive infection often bear long-term effects, such as seizures and hardened paw pads.