Abstract
Restriction endonuclease cleavage analysis of three salmonid herpesvirus (strain H-83, OO-7812 strain of Oncorhynchus masou virus (OMV) and Herpesvirus salmonis) DNAs was performed by using DNA extracted directly from virus-infected cells. Clear-cut cleavage patterns were obtained when DNA was extracted from approximately 1.1×105 cells infected with the viruses, and the patterns were unique for each herpesvirus. After passages of strain H-83 and OMV for 33 and 36 times in vitro, respectively, some fragments were noted to appear or disappear. However, no DNA fragment of H. salmonis changed during the 36th passage. During the second passage levels, strain H-83 and OMV showed high virulence in masu salmon (O. masou) fry (100% mortality by 27 days postinoculation), whereas the viruses showed a decrease in virulence even at more than 33 passage levels.
