Representative histopathological sections of lung from each infected group (200×). Healthy control group (A) and PCV2 group (B): no evident pathological changes. HP-PRRSV group (C), HP-PRRSV+PCV2 group (D), and PCV2/HP-PRRSV group (E) showed the same pathological changes: interstitial pneumonia and some stenosis or obstruction of the pulmonary alveoli. (F) The HP-PRRSV/PCV2 group had the most-severe pathological changes: severe congestion in small vessels and stenosis or obstruction of most pulmonary alveoli, which were full of necrotic and deciduous endothelial cells. Hematoxylin and eosin (HE) staining.