Histopathological changes in piglets infected with each virulent RVA strain or after challenge following immunization. (A, E, I) Duodenum, jejunum, and ileum of mock-inoculated piglets showed villi of normal length and no crypt hyperplasia. (B–D, F–H, and J–L) Duodenum (B–D), jejunum (F–H), and ileum (J–L) sampled at 7 dpi from piglets inoculated with virulent strains 174-1, PRG942, or K71 showed severe villous atrophy, moderate crypt hyperplasia, and severe lymphoid cell infiltrations in the lamina propria. (M–X) Duodenum (M–P), jejunum (Q–T), and ileum (U–X) sampled at 28 dpv from piglets first immunized with one of the live attenuated monovalent or trivalent vaccines and then challenged with the corresponding original virulent strain(s) 174-1, K71 or PRG942 showed villi of normal length, mild crypt hyperplasia, and mild infiltrations of lymphoid cells in the lamina propria in a manner similar to that of the mock-inoculated group. Hematoxylin and eosin stain. Bars = 200 μm.