FIG 6.

Histopathological examinations. (A) Samples from a normal duck. (B) Samples from a duck infected with the wild-type strain Yb2, at 48 hpi. (C) Samples from a duck infected with the mutant strain Yb2ΔpncA, at 48 hpi. (D) Samples from a duck infected with the complemented strain cYb2ΔpncA, at 48 hpi. No pathological changes were observed in the tissues of Yb2ΔpncA-infected ducks. In Yb2- or cYb2ΔpncA-infected ducks, pathological changes, including inflammatory cell infiltration, hemorrhage, cellular edema, and fibrinous exudate, were observed in the heart (black arrows), while vacuolar degeneration in hepatocytes was observed in the liver (red arrows) and diffuse vacuolation and decreased cellularity were found in the spleen (green arrows). The tissues were stained with hematoxylin and eosin. Magnification, ×200.