Cellular targets and pathways of yellow head virus infection in lymphoid organ of Penaeus monodon as studied by transmission electron microscopy

Negative-stained intact yellow head virus (YHV) was an enveloped bacilliform particle measuring 40-50 x 175-210 nmwith spike-like projections measuring 7-9 nm. The space between projections was 4-7 nm. YHV nucleocapsid was rod-shaped,measuring 35-40 x 160-200 nm, and the RNA genome had 40-50 turns in a helical structure. YHV infected both stromal matrixcells and haemocytes in the lymphoid tubule wall. The patterns of localisation of viral particles were similar in both cells. Thefully enveloped viral particles were detected at the cell membrane, endosome, rough endoplasmic reticulum, Golgi complexand secretory vesicles, and virions were exocytosed at the cell membrane. In the case of severe infection, unenveloped viralparticles could be detected in the cytoplasm, and they might be released by general breakdown and lysis of the highly infectedcells