Characterization of virus distribution in Rock Bream (Oplegnathus fasciatus; Temminck and Schlegel) infected with megalocytivirus.

The distribution of virus-infected cells in the organs of Rock Bream naturally infected with megalocytivirus is reported. Examination of sections of liver, spleen and kidney stained by haematoxylin and eosin (HE) and periodic acid Schiff (PAS) revealed the presence of swollen and degenerate cells having morphology consistent with leucocytes. Many of these cells were shown to contain viral DNA by in-situ hybridization (ISH). Cells containing viral DNA were also found in the connective tissue of other organs in which there was no prominent infiltrate of degenerate leucocytes. Viral DNA was also found in the cytoplasm of leucocytes in blood smears. Transmission electron microscopy (TEM) confirmed the presence of viral particles in the cells within tissue and free within blood. The tissue distribution of virus in this infection is suggested to reflect the infiltration of virus-infected leucocytes.