Herpesvirus salmonis: Characterization of a new pathogen of rainbow trout

A new agent, provisionally designated Herpesvirus salmonis, was isolated from post-spawning rainbow trout (Salmo gairdneri) and studied primarily in the RTG-2 rainbow trout cell line. Infection of RTG-2 cells resulted in the formation of syncytia and Cowdry type A intranuclear inclusions. Replication occurred regularly at 5 and 10°C, but was inconsistent at 15°C, largely inhibited at 0°C, and completely inhibited at 20°C or higher. The virus was acid, heat, ether, and chloroform labile, but stable to freezing and thawing. It did not hemagglutinate. Viral DNA had a buoyant density of 1.709 g/cm³ and a guanine-cytosine value of 50%. Hexagonal nucleocapsids had a diameter of 90 nm and were first seen in nuclei at 36 h. Enveloped forms measured about 150 nm and occurred both cytoplasmically and extracellularly. At 10°C, a one-step growth culture required about 96 h; cell-associated virus peaked at about 10⁵ PFU/ml and exceeded released virus by a factor of about 10.