Virus shedding and replication in the respiratory tract of ferrets inoculated with 1918 influenza H1N1 virus. Ferrets were inoculated intranasally with 106 50% tissue culture infectious dose (TCID50) of 1918 H1N1 influenza virus. A, Virus titers in nose and throat swabs collected at 1, 3, 5, and 7 days postinoculation (dpi) from 4 ferrets euthanized at 7 dpi. Horizontal lines represent geometric mean titers. B, Virus titers in the nasal turbinates, trachea, and lung at 1, 3, 5, and 7 dpi. Horizontal lines represent geometric mean titers. C, Detection of influenza A virus nucleoprotein in the epithelium of the nasal respiratory mucosa, olfactory mucosa, bronchus, bronchioles, and alveoli at 1, 3, 5, and 7 dpi. An asterisk (*) in the respiratory mucosa indicates the detection of influenza virus antigen in sloughed-off epithelial cells. An arrowhead in the olfactory mucosa indicates influenza virus antigen in individual cells. An asterisk in the bronchus indicates influenza virus antigen in the submucosal glands.
