Expression and self-assembly of virus-like particles from two genotypes of marine vesiviruses and development of an ELISA for the detection of antibodies.

Sequences encoding the major and minor capsid proteins (VP1 and VP2) from two marine vesivirus isolates (Steller sea lion viruses V810 and V1415) were engineered for expression of virus-like particles (VLPs) in the baculovirus system. The resulting VLPs were morphologically similar to native vesivirus virions. Purified VLPs were probed in immunoblots with pooled antisera specific for nine San Miguel sea lion virus (SMSV) types, and a predominant protein of approximately 60kDa was detected. An enzyme linked immunosorbent assay (ELISA) for the detection of antibodies was developed in which the VLPs served as antigen. The VLPs were adsorbed to the wells of a microplate, and the specificity of the ELISA was established with hyperimmune sera raised against 24 serotypes of the genus Vesivirus. The ELISA was used to screen for the presence of vesivirus specific antibodies in the sera of free-ranging Steller sea lions. The ELISA results demonstrated that Steller sea lions that inhabit the Pacific Ocean waters of southeast Alaska are widely exposed to antigenically related marine vesiviruses, while no previous exposure could be demonstrated using VLP antigens in 17 Steller sea lions from the Aleutian Islands. The broad reactivity of these VLPs and their non-infectious nature will facilitate global sero-epidemiological studies aimed at determining the incidence and prevalence of marine vesiviruses in mammals that inhabit the Pacific and Atlantic oceans as well as susceptible terrestrial animals.