Microscopic lesions in the placenta.
A Mild placentitis from a ewe challenged at 40 dg (G1). It is characterized by serum leakage between the maternal and foetal tissues, focal necrosis of foetal villi and non-purulent inflammation in the adjacent maternal septum. B Moderate to severe placentitis from a ewe challenged at 90 dg (G2). The lesion is denoted by large area of necrosis affecting both maternal and foetal villi and scarce infiltration of inflammatory cells.