Age-related susceptibility to infection with canine distemper virus in gnotobiotic dogs

The influence of age on the susceptibility of gnotobiotic dogs to infection with virulent canine distemper virus (R252-CDV) was studied. Of the dogs infected at less than one week of age, 85% died of acute encephalitis two to five weeks after infection. In contrast, only 28.5% of infected weanling and 33.3% of infected adult dogs died after receiving inoculations of R252-CDV. Furthermore, about one-half of the fatally infected weanling dogs developed chronic encephalitis characterized by infiltration of lymphocytes and plasma cells in areas where demyelination of the central nervous system had occurred. Age-related susceptibility correlated with in vitro responses of peripheral blood lymphocytes to phytomitogens. The results of this study suggest that physiological immaturity of the immune system of neonatal dogs may account for their increased susceptibility to infection with CDV.