H7N9 virus is transmissible among mice by direct contact. Seven naïve mice were placed in direct contact with three mice infected with 106 TCID50 of H7N9 virus. (a) IHC observations in tissues of mice exposed to H7N9-infected mice. Viral antigen distribution in tissues at 5 days following exposure to infected mice. Viral antigens are denoted with solid arrows (400× magnification). Viral antigens are within the epithelial cells of the bronchi and small intestinal villi, and within infiltrating inflammatory cells of the small intestine. (b) HE staining of lung tissue from mice that came in contact with H7N9-infected mice (100× magnification). At 3 days after coming into contact with infected mice, mild dilation of the interstitial pulmonary vasculature was observed in the lungs; congestion was observed after 7 days.