A puzzle across space and time: piecing together the microbial ecology of sea star wasting disease

Starting in 2013 and continuing to the present day, sea star wasting disease (SSWD) has affected > 20 species of asteroids from Alaska to Baja California, and potentially elsewhere in the eastern Pacific Ocean and North... [ view full abstract ]

Starting in 2013 and continuing to the present day, sea star wasting disease (SSWD) has affected > 20 species of asteroids from Alaska to Baja California, and potentially elsewhere in the eastern Pacific Ocean and North Atlantic Ocean. Through comparative metagenomic, quantitative epidemiological, and size-based challenge, SSWD has been associated with viral infection, and the most likely candidate virus is the sea star associated densovirus (SSaDV). Work on understanding disease pathology and epidemiology was stifled by a lack of representative tissue or cell cultures, and lack of any unexposed asteroid populations upon study initiation. We applied quantitative PCR targeting multiple loci of the SSaDV genome against tissues dissected from SSaDV-negative asymptomatic, SSaDV-positive asymptomatic and SSaDV-positive symptomatic individuals (representing two disease stages). Our data show that SSaDV is primarily found in digestive glands, ampullae and papillae of SSaDV-positive, asymptomatic animals, but can be found in gonads, coelomic epithelium and body wall lesion margins in later-staged symptomatic individuals. Geographic and historical surveys of loci by qPCR revealed the presence of the ~100 bp fragment of each gene in specimens dating back to 1980, but by conventional PCR, SSaDV’s structural and replication-associated genes were found only in contemporary specimens and in a single specimen from 1980. Similarly, the 100 bp fragment of SSaDV’s NS1 and VP4 were detected in geographically widespread sea star populations, but the full sequence only recovered from specimens from the contemporary epidemic and, interestingly, from specimens from the Eastern Pacific. Work is currently underway to study time-course variation in microbiome structure and host response, as well as understanding host size of tissue-level distribution of SSaDV.