Roniviridae

This chapter focuses on Roniviridae family whose sole member genus is Okavirus. The virions are enveloped and bacilliform in shape with rounded ends, where the envelope is studded with prominent peplomers projecting approximately 11 nm from the surface. The nucleocapsids are 20–30 nm in diameter and have a helical symmetry with coil periodicity of 5–7 nm. Long filamentous nucleocapsid precursors occur in the cytoplasm of infected cells and acquire envelopes by budding at endoplasmic reticulum membranes. The virions are sensitive to calcium hypochlorite and sodium dodecyl-sulfate, but sensitivity to other treatments is not known. The virions possess a lipid envelope derived from endoplasmic membranes of host cells. Compared to the genomes of vertebrate nidoviruses, the okavirus genome is unique in that the nucleoprotein gene (ORF2) is located upstream of the glycoprotein gene (ORF3), there is no discrete gene encoding a structural membrane (M) protein, and the virion envelope glycoproteins gp116 and gp64 are generated by proteolysis of a pp3 precursor polyprotein encoded by the ORF3 gene. Okaviruses have been detected only in crustaceans and their geographic range mirrors that of its primary penaeid host, extending across the Indo-Pacific from Eastern Africa, Southern and Southeast Asia, and Australia to islands in the South Pacific. Infections have also been detected recently in blue shrimp (P. stylirostris) from the Gulf of California, and they may be chronic or acute and transmitted horizontally or vertically.