The Caliciviridae is a diverse family of viruses with a wide host range including humans, cats, dogs, swine, marine mammals, amphibians, fish, and reptiles. The Vesivirus genus of this family is of particular interest due to the ability to infect both aquatic and terrestrial hosts, cause vesicular disease in livestock, and because of its zoonotic potential. The goals of this doctoral research were to isolate and characterize currently circulating vesiviruses in marine mammals and use these data to develop improved diagnostic assays for the molecular and serological detection of these viruses.
We isolated and characterized two novel marine vesiviruses from Steller sea lions (Eumetopias jubatus) from Alaska. Through full genomic sequencing and phylogenetic analyses, we identified conserved and variable domains in the Vesivirus genomes and determined genetic relationships among the marine vesiviruses. We also partially characterized, through nucleotide sequencing, two other marine vesivirus serotypes that had previously not been analyzed.
With the molecular data obtained from the genetic characterization, two novel diagnostic assays were developed for the marine vesiviruses. A real-time RT-PCR assay was developed as a rapid, sensitive, specific, and quantitative molecular assay for the detection of the marine vesiviruses. This assay specifically detected different serotypes of marine vesiviruses, and can distinguish them from other agents causing vesicular disease in marine mammals or livestock.
We also developed a serological assay in the form of an enzyme linked immunosorbent assay (ELISA). The novel vesiviruses were used to produce virus-like particles (VLPs); the first demonstration of these structures for the marine vesiviruses. The VLPs are non-infectious proteins, which are virtually identical to the native virions and can be used as viral antigens. This ELISA was cross-reactive with many different marine vesiviruses, and detected antibodies to these viruses in serum from marine mammals.
Thus far, these viruses have only been isolated from marine mammals in the Pacific Ocean. Through our collaboration with organizations within the Southeastern United States, we tested marine mammal samples from the Atlantic Ocean and Gulf of Mexico to potentially determine viral presence. We tested 223 samples and did not find any evidence of vesivirus activity in these waters.