Pathogenesis and immunogenicity of bovine adenovirus type 3 in cotton rats (Sigmodon hispidus)

Intranasal inoculation of cotton rats (Sigmodon hispidus) with 10(8) PFU of bovine adenovirus type 3 (BAd3) resulted in limited virus replication in the lung and trachea. Histopathological changes in the lungs were characterized by necrosis and hyperplasia of bronchiolar epithelium, eosinophilic intranuclear inclusions, pneumocyte type II hyperplasia in the alveoli, and mild peribronchiolar and perivascular lymphocytic infiltration. Immunohistochemically, viral antigens were observed more frequently in bronchiolar epithelial cells than in alveolar cells in cotton rat lung sections stained using a rabbit anti-BAd3 serum. Bronchiolar epithelial changes, intranuclear inclusion bodies, type II pneumocyte proliferation, peribronchiolar infiltration, and immunohistological staining were maximum at Day 3 or Day 4 postinoculation, whereas perivascular infiltration was first observed at Day 8 postinoculation. In addition to the histological study of the pathogenesis of BAd3 infection, we monitored the BAd3-specific immune response in cotton rats. Anti-BAd3 IgG and virus neutralizing antibodies were detected in sera, whereas anti-BAd3 IgA antibodies were found in the sera, lung, and nasal washes. Our results suggest that the cotton rat can serve as a useful small-animal model for investigating the pathogenesis of BAd3 infection, as well as immune responses to BAd3 recombinant virus vaccines.