Canine distemper virus-associated cardiac necrosis in the dog.

An age-related canine distemper virus-associated cardiomyopathy characterized by multifocal myocardial degeneration necrosis and mineralization with minimal inflammatory cell response was found in gnotobiotic Beagle pups. Of the 30 dogs infected experimentally at 5 to 7 days of age with virulent R252 strain of canine distemper virus, 11 had gross or microscopic cardiac involvement as early as 16 days post-infection. The 25 dogs similarly infected at 10 to 21 days of age, the uninfected age-matched controls, and pups infected at 5 to 7 days of age with avirulent R252 canine distemper virus had no cardiac lesions. Although the lesions are attributed to a direct viral effect, they occur against a background of other canine distemper virus-related changes including immunosuppression, anemia and encephalomyelitis. All these factors may have a modifying role in the development of this age dependent susceptibility to virus-associated myocardial necrosis.