Comparative histopathology of draining lymph node after infection with virulent or attenuated strains of Salmonella abortusovis in lambs.

Histological responses to the early phase of infection were compared in parotid lymph nodes of lambs infected by the subcutaneous route into the right eyelid with either a virulent or an attenuated strain of Salmonella abortusovis. The right parotid lymph nodes showed a massive PMN infiltration for the first days of infection for both strains. From day 6, the infected lymph nodes developed a lymphoid hyperplasia with prominent germinal centers independent of strain type. The virulent strain of S. abortusovis induced focal lesions in 2 out of 6 lambs necropsied on days 6 and 10, and provoked a systemic infection evidenced by the regular colonization of spleen on day 6. In contrast, no focal lesion and a restricted bacterial dissemination were observed in lambs infected with the vaccinal strain.