Canine Distemper Canine distemper is caused by a virus that is shed in bodily fluids of infected animals. The virus affects primarily the lungs, intestines, and nervous system. Symptoms of the infection can include coughing, diarrhea, vomiting, inappetance, dehydration, weight loss, seizures, and encephalitis. Secondary infections can present as discharge from the eyes and/or nose, and pneumonia. Puppies, especially those from shelters, are at the highest risk. Currently there are no antiviral medications to treat canine distemper. Treatment is aimed at controlling secondary bacterial infections with antibiotics and supportive care as needed. Vaccination aimed at preventing distemper is the best strategy. Puppies should be isolated from other dogs until they have completed their series of vaccinations at 16 weeks of age.