Gross pathological and histopathological changes
Compared with the piglets in the immunized-challenge groups (A1 and A2) (Fig. 6A b, h and Fig. 6B n, t) and negative control groups (C1 and C2) (Fig. 6A c, i and Fig. 6B o, u), the piglets in the challenge groups (B1 and B2) showed lesions typical of PRRS, such as consolidation in the lungs and haemorrhaging in the lymph nodes (Fig. 6A a, g and Fig. 6B m, s). Histopathology revealed a large amount of inflammatory cell infiltration, epithelial cell proliferation and significant alveolar diaphragm widening in the lungs (Fig. 6A d, p) and decreased lymphocyte and medullary bleeding in the lymph nodes (Fig. 6A j, v) in the challenge groups (B1 and B2) compared with the negative control groups (Fig. 6A f, l and Fig. 6B r, x). Notably, there was almost no pathological damage to the lungs (Fig. 6A e and Fig. 6B q) and only mildly decreased levels of lymphocytes in the immunized-challenge groups (A1 and A2) (Fig. 6A k and Fig. 6B w).