distemper, in veterinary medicine, highly contagious, catarrhal, often fatal disease of dogs. It also affects wolves, foxes, mink, raccoons, and ferrets. Distemper is caused by a filtrable virus that is airborne; it is also spread by infected utensils, brushes, and clothing. Symptoms are high fever, apathy, and lack of appetite with resulting dehydration and loss of weight. The respiratory and gastrointestinal tracts become involved, and there is vomiting and diarrhea. A dog may recover from the above signs and then develop nervous complications, i.e., convulsions, localized muscular twitches, weakness, and paralysis. Distemper in dogs can be controlled by immunizing each animal as early as possible with a modified live-virus vaccine.