Okavirus is a genus of enveloped positive-strand RNA viruses which infect crustaceans.

[2] Viruses associated with the genus include: gill-associated virus (GAV) which causes reddening, biofouling with exoparasites, emaciation, and massive mortality; and yellow head virus (YHV) which causes yellow head, arrest of feeding, and massive mortality.

[1][3] The name is derived from the 'Oka' or lymphoid organ in which the viruses are commonly detected and in which pathology occurs during acute infections.

Lymphoid organs are anatomical structures common to penaeid shrimp.

[1] Viruses in the genus Okavirus are enveloped, with bacilliform geometries, and helical symmetry.