Herpes viruses infecting bivalves: A review

摘要

Particles morphologically similar to herpes viruses were first detected in an invertebrate (the Eastern oyster, Crassostrea vir-ginica) in 1972. Herpes-like viruses have since been identified in various marine bivalve species throughout the world, including the Pacific oyster, Crassostrea gigas, the European flat oyster, Ostrea edulis, the Antipodean flat oyster, Ostrea angasi, the Chilean oyster, Tiostrea chilensis, the carpet shell clam, Ruditapes decussatus, the Manila clam, Ruditapes philippinarum and the great scallop, Pecten maximus. Infections are often associated with sporadic episodes of high mortality among larvae and juveniles. PCR-based diagnostic methods have facilitated epidemiological investigations showing that healthy adult animals can harbour the viral genome. Transmission experiments have demonstrated the pathogenicity of the virus, and indicated that a single species is probably responsible for all the infections observed. The virus isolated from infected C. gigas larvae has been formally classified as a member of the Herpesviridae under the name ostreid herpesvirus 1 (OsHV-1). Characterization of the genome yielded an estimated size of 207 kbp. The capsid morphology and genome sequence of OsHV-1 have been studied in order to assess its phylogenetic status in relation to vertebrate herpes viruses. The conserved gene that comes closest to being herpes virus-specific encodes the putative ATPase subunit of the terminase, an enzyme complex involved in packaging viral DNA into preformed capsids. Moreover, similarities between the two groups in capsid structure and mechanisms of capsid maturation tip the balance of evidence in favour of a common origin.