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Bovine Adenovirus Type 3 Pneumonia in Dexamethasone-treated Calves

National Institute of Animal Health, Shichinohe, Kamikita, Aomori 039-2586, Japan

The effects of immunosuppression were examined in 1.5-month-old calves that were given dexamethasone (DM) before endobronchial inoculation with bovine adenovirus type 3 (BAV-3). Immunohistopathologically, severe necrotizing bronchiolitis with eosinophilic and basophilic intranuclear inclusion bodies was observed both in DM-treated 1.5-month-old infected calves and in non–DM-treated 7-day-old infected calves. These inclusion bodies were correlated with the detection of BAV-3 antigen and viral particles. The presence of inclusion bodies in the desquamated epithelial cells or of BAV-3 antigen, or both, correlated well with the isolated level of BAV-3 in bronchoalveolar lavage (BAL) fluid. Few immunoglobulin (IgG, IgM, and IgA)-containing B lymphocytes or CD8+ T lymphocytes infiltrated the pneumonic lesion in both the 7-day-old and the DM-treated 1.5-month-old infected calves. Thus, depletion of CD8+ T lymphocytes in calves might influence the clearance of BAV-3 from respiratory tissues.

Key words: Bovine adenovirus type 3; bronchoalveolar lavage fluid; calves; CD8; dexamethasone treatment; immunohistochemistry; pneumonia.

Request reprints from Dr. Minoru Narita, National Institute of Animal Health, Shichinohe, Kamikita, Aomori 039-2586 (Japan). E-mail: mnarita{at}affrc.go.jp.