Figure 4: Results of histopathological examination. Piglets from sows with or without prepartum immunization with inactivated S. suis 2+rSao were challenged with heterologous S. suis serotype 1 bacteria at the 5 weeks of age. The histopathological examination was performed on the 7th day after the challenge. Control pigs manifested severe brain and lung lesions, including slight vascular congestion on the brain meninges and shedded epithelial cells in the lung alveolar space.