Evaluation of blue mussel Mytilus edulis as vector for viral hemorrhagic septicemia virus (VHSV).

When viral diseases occur in aquaculture farms, the virus released into the seawater from infected animals can re-infect other susceptible species or accumulate in filter-feeding organisms. We conducted a viral hemorrhagic septicemia virus (VHSV) survivability analysis of blue mussel Mytilus edulis digestive enzymes, viral depuration, and infectivity tests via in vitro and in vivo inoculation to evaluate the infectious state. VHSV particles were not completely digested within 24 h in vitro and were maintained for 7 d in the mussel digestive gland. Mussels cohabitating with naturally VHSV-infected olive flounder Paralichthys olivaceus could accumulate the viral particles. Although the viral particles in the gill as the entrance of filter-feeding organisms are infectious, the presence of these particles in the digestive gland were not able to induce cytopathic effects in vitro. Viral particles detected by RT-PCR from bivalve mollusks (Pacific oyster Crassostrea gigas and mussel) from the field did not produce cytopathic effects in cell culture and did not replicate after intraperitoneal injection into olive flounder. Therefore, VHSV particles in blue mussel might be in a non-infectious stage and the possibilities of VHSV transmission to fish under field conditions are scarce.