Fish Diseases and Management

5.4.4 Togaviruses

Toga - like viruses are observed in the lesions of lymphoid organs of many shrimps (P. monodon, P. esculentus, P. vannamei, P. stylirostris, and P. chinensis). Extreme hyperplasia and metastasis of the lymphoid organ (Oka organ) can be histologically recognised in the lesions. The virus particles of 30 nm diameter was observed in intracytoplasmic eosinophilic to pale basophilic cytoplasmic inclusion bodies occurring in cells with highly vacuolated cytoplasm. Cells were found to have pyknotic and karyorrhetic nuclei. The virus particles of 55 mm diameter are produced either by budding or by invagination and fusion of host cell membranes around the nucleocapsids.