Surveillance of Type 1 Ostreid Herpesvirus (OsHV-1) Variants in Japan

Ostreid herpesvirus 1 (OsHV-1) mu Var is a variant of OsHV-1 and suspected of being the causative agent of acute mass mortality events of Pacific oysters during summers in Europe since 2008. In this study, the distribution of OsHV-1 was surveyed in the six main oyster-producing areas of Japan, using PCR targeting a C2/C6 fragment including ORF4. PCR products were amplified from 123 out of 1,714 oysters of three species of Crassostrea (C. gigas, C. sikamea and C. ariakensis), and 23 different nucleotide sequences, showing 96% to 99% similarity to the reference OsHV-1, were obtained. Although 18 sequences among the 23 obtained possessed a microsatellite deletion unique to OsHV-1 mu Var, all PCR products contained two conserved nucleotides that were shared with the reference OsHV1 and not with OsHV-1 mu Var. Here, we found variable types of OsHV-1 in oysters in Japan, but their nucleotide sequences were not identical to those of OsHV-1 mu Var.