A highly prevalent and pervasive densovirus discovered among sea stars from the North American Atlantic Coast
Viral metagenomes prepared from tissues from Forbes sea star (Asterias forbesi) led to the discovery of a complete genome of a novel sea star densovirus (AfaDV). The genome organization of AfaDV and phylogenetic analysis place this virus among the Ambidensovirus genus in the subfamily Densoviridae, family Parvoviridae. AfaDV shares 78% nucleotide pairwise identity to the sea star associated densovirus (SSaDV), previously described as the putative causative agent of Sea Star Wasting Syndrome among sea stars from the Northwest Pacific. SSaDV was not found in specimens collected in this study, and the discovery of AfaDV might explain previous reports of SSaDV among sea stars from the Atlantic Coast. A qPCR assay was designed to assess tissue tropism, host specificity, and prevalence of AfaDV among wild populations of sea stars at five locations on the North American Atlantic Coast. AfaDV was detected in all three common sea star species (Asterias forbesi, Asterias rubens, and Henricia sp.) found in the region and was highly prevalent (80-100% of individuals tested, n=134), among populations collected at disparate sites 7 years apart. AfaDV was detected in the body wall, gonads, and pyloric caeca (digestive gland) of specimens but was not detected in their coelomic fluid. A significant difference in viral load was found between tissue types with the pyloric caeca having the highest viral load suggesting it is the primary site of viral replication in the animal. Further investigation of Asterias forbesi gonad tissue found germline cells (oocytes) to be virus positive suggesting a potential route of vertical transmission. Taken together, these observations show that the presence AfaDV is not an indicator of Sea Star Wasting Syndrome because AfaDV is a common constituent of these animals microbiome, regardless of health. These results broaden the understanding of echinoderm densoviruses outside the context of disease that suggest these viruses might form commensal or mutualistic relationships with their hosts.