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The cotton rat as an experimental model of human parainfluenza virus type 3 disease.

Intranasal or aerosol inoculation of cotton rats (Sigmodon hispidus) with human parainfluenza virus type 3 (P3) produces pulmonary changes which closely resemble human disease due to this agent. Active viral replication resulted in peak titers by day 2 of infection. Viral antigen was localized by immunofluorescence in bronchial epithelial cells alone (aerosol inoculation) or epithelial and alveolar cells (intranasal instillation). Cytopathic effects in epithelial cells was noted as early as day 2, and marked cellular proliferation occurred by day 7. Intranasal instillation of virus resulted in development of patchy interstitial pneumonitis. Mononuclear cell infiltration in the peribronchial and perivascular areas peaked on days 6 and 7. A brisk systemic antibody response was measured both by complement fixation and virus neutralization techniques. These data establish the value of the cotton rat as an experimental model for the study of bronchiolitis and pneumonia due to P3. Since previous work has demonstrated that respiratory syncytial virus and Mycoplasma pneumoniae also will replicate and cause pulmonary disease in cotton rats, comparative studies in a single animal species are facilitated.