An epizootic of parainfluenza virus type 1 in a group of C57B16 mice.

An epizootic of respiratory troubles was noticed in a group of C57B16 mice used to study their response following inoculations of different thymic extracts. The infection was characterized by a high level of mortalities. Macroscopically, the lungs of affected animals showed red consolidated areas on the lobes. Microscopically, an acute bronchopneumonia with eosinophilic intracytoplasmic inclusion bodies in the epithelial cells of the bronchi were seen. Those lesions suggest a parainfluenza virus type 1 infection. The presence of viral particles, morphologically similar to members of the Paramyxoviridae family in lung homogenates observed under electron microscopy and the elevated serum complement fixation and hemagglutination inhibition antibody titers to parainfluenza virus type 1 confirm the diagnosis. The source of the infection is unknown but four hypothesis are proposed. Healthy animals free of demonstrable antibodies specific to parainfluenza virus type 1 were obtained and the experiment was repeated. No mortalities were observed and the animals remained free of demonstrable complement fixation and hemagglutination inhibition antibodies throughout the experiment.