Purification and partial genome characterization of a herpes-like virus infecting the Japanese oyster, Crassostrea gigas

First observed in 1972 in Crassostrea virginica, herpes-like viruses of bivalves were more recently found to be associated with high mortality rates in other cultured oyster species, such as Crassostrea gigas and Ostrea edulis. The diagnosis of herpes-like virus infections is performed currently by laborious histological and transmission electron microscope examinations. Preparation of specific reagents for use in more amenable diagnostic techniques prompted purification of virus particles and investigation of the viral genome. This paper is the first description of the purification of a virus pathogen from a bivalve mollusc. A procedure was developed which facilitated purification of large amounts of virus particles on the 40-50% interface of sucrose gradients. Transmission electron microscopy showed that a purified virus suspension contained capsids and enveloped virus particles. High molecular mass viral DNA was extracted and the genome size was estimated by the summation of the sizes of restriction endonuclease fragments to be approximately 180 kbp. Partial cloning of the virus genome was achieved and the specificity of certain cloned fragments was established by dot blot hybridization.