In contrast, macroscopic changes have not been reported for fetuses infected after they become immunocompetent for PPV. Microscopic lesions are primarily endothelial hypertrophy and mononuclear cell infiltrations consistent with an immune response. Meningoencephalitis characterized by perivascular cuffing with proliferating adventitial cells, histiocytes, and a few plasma cells was seen in the gray and white matter of the cerebrum and in the leptomeninges of PPV-infected stillborn pigs. These lesions were believed to be pathognomonic for PPV infection. Similar lesions have been observed in PPV-infected, live fetuses collected late in gestation (Fig. 7B).