REPLICATION OF A HERPES-LIKE VIRUS IN LARVAE OF THE FLAT OYSTER TIOSTREA-CHILENSIS AT AMBIENT-TEMPERATURES

Veligers removed from brooding Tiostrea chilensis (Philippi, 1845) exp erienced similar to 95% mortalities over 3 to 4 d at 16 to 18 degrees C that appeared to be associated with a herpes-like virus. Ultrastruct ural observations of post-removal veligers showed the presence of earl y viral replication or putative latent stages at 4 h, all stages of re plication at low levels at 24 h, which increased to high levels at 48 h, followed by mortalities at 72 h onwards. Initially, infected inters titial or epithelial cells had an enlarged nucleus with a wavy outline in which heterochromatin was marginated. With continued increase in s ize, nuclei became smooth in outline with reduction or loss of heteroc hromatin. Capsids with lucent cores (LCC) and empty capsids appeared i n the nucleus, often in association with tubular structures similar to 65 nm in diameter that were composed of subunits in a helical configu ration that contained a tubular core similar to 35 nm in diameter. Emp ty capsids and LCC sometimes occurred in paracrystalline arrays. Parti al nucleolar disaggregation and encapsidation of dense fibrillar mater ial preceded envelopment entering and de-envelopment leaving the perin uclear cisterna, tegumentation in cytoplasmic vesicles, and egress. Gr oups of dense cytoplasmic filaments 30 to 35 nm in diameter occurred i n some infected cells. Apparently normal cells with a few intranuclear empty capsids and/or LCC at 4 h post-removal may represent latent inf ections. Replication was not observed in larvae held at 24 to 27 degre es C, but a few cells had enlarged hypochromatic karyolytic nuclei, an d 1 to 2 capsids were observed in them, at 48 h. Viral replication was similar to that of ranid herpesvirus 1 (Lucke tumour) infections. Thi s is the fifth ostreid species from which herpesviruses have been repo rted.