Discovery of two novel densoviruses associated with sea star wasting disease of Asterias forbesi and Asterias amurensis

Sea stars are susceptible to a disease commonly known as sea star wasting disease (SSWD) that has been reported in the literature since the 1970s. In 2013, a mass mortality event of sea stars occurred from Baja, California to... [ view full abstract ]

Sea stars are susceptible to a disease commonly known as sea star wasting disease (SSWD) that has been reported in the literature since the 1970s. In 2013, a mass mortality event of sea stars occurred from Baja, California to Alaska affecting >20 species, and SSWD has now become the most geographically widespread marine epizootic recorded. It is unclear whether the sporadic disease events in the past are linked or caused by the same etiological agent to present day disease events nevertheless the signs of disease have remained consistent. Prior to 2013 the causative agents and contributing environmental factors of SSWD were mostly uninvestigated. Using culture-independent approaches, the “sea star associated densovirus (SSaDV)”, was discovered and significantly correlated to the disease, and SSWD signs were inducible through challenge of asymptomatic individuals with virus-sized material. Since 2013, researchers have recently observed sea stars dying of signs similar to SSWD from Australia, China and the east coast of North America. Viral metagenomic surveys were conducted from tissues of two affected species, Asterias forbesi and Asterias amurensis, from the east coast of the United States and China, respectively, in attempt to understand the association between viruses and these SSWD occurrences. Two novel genomes were recovered from each species showing >80% nucleotide identity to SSaDV. The genome architecture of both densoviruses were similar to SSaDV. Each genome contained two ORFS exhibiting ambisense directionality and each bore ORFs encoding for NS1, VP4 and a hypothetical protein mostly likely VP1. The pathogenicity of these viruses remains unknown, but the results from this study further the co-occurrence between sea star associated densoviruses and the sea star wasting disease.