Jackson EW et al. (2020), A Highly Prevalent and Pervasive Densovirus Dis...

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Appl Environ Microbiol 2020 Mar 02;866:. doi: 10.1128/AEM.02723-19.

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A Highly Prevalent and Pervasive Densovirus Discovered among Sea Stars from the North American Atlantic Coast.

Jackson EW , Pepe-Ranney C , Johnson MR , Distel DL , Hewson I .

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The etiology of sea star wasting syndrome is hypothesized to be caused by a densovirus, sea star-associated densovirus (SSaDV), that has previously been reported on the Pacific and Atlantic Coasts of the United States. In this study, we reevaluated the presence of SSaDV among sea stars from the North American Atlantic Coast and in doing so discovered a novel densovirus that we have named Asterias forbesi-associated densovirus (AfaDV), which shares 78% nucleotide pairwise identity with SSaDV. In contrast to previous studies, SSaDV was not detected in sea stars from the North American Atlantic Coast. Using a variety of PCR-based techniques, we investigated the tissue tropism, host specificity, and prevalence of AfaDV among populations of sea stars at five locations along the Atlantic Coast. AfaDV was detected in three sea star species (Asterias forbesi, Asterias rubens, and Henricia sp.) found in this region and was highly prevalent (>80% of individuals tested; n = 134), among sampled populations. 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 (copies mg-1) was found between tissue types, with the pyloric caeca having the highest viral loads. Further investigation of Asterias forbesi gonad tissue found germ line cells (oocytes) to be virus positive, suggesting a potential route of vertical transmission. Taken together, these observations show that the presence of AfaDV is not an indicator of sea star wasting syndrome because AfaDV is a common constituent of these animals'' microbiome, regardless of health.IMPORTANCE Sea star wasting syndrome is a disease primarily observed on the Pacific and Atlantic Coasts of North America that has significantly impacted sea star populations. The etiology of this disease is unknown, although it is hypothesized to be caused by a densovirus, SSaDV. However, previous studies have not found a correlation between SSaDV and sea star wasting syndrome on the North American Atlantic Coast. This study suggests that this observation may be explained by the presence of a genetically similar densovirus, AfaDV, that may have confounded previous studies. SSaDV was not present in sea stars screened in this study, and instead, AfaDV was commonly found in sea star populations across the New England region, with no apparent signs of disease. These results suggest that sea star densoviruses may be common constituents of the animals'' microbiome, and the diversity and extent of these viruses among wild populations may be greater than previously recognized.

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Genes referenced: LOC100887844

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	FIG 1. Genome architecture and base coverage of Asterias forbesi-associated densovirus (AfaDV). (Top) Structural hairpins 88 nt long located in the inverted terminal repeats at the end of the genome. (Middle) Genome organization with ORFs colored by putative function. Red corresponds to the structural protein (VP), and blue corresponds to nonstructural proteins (NS1, NS2, and NS3). (Bottom) Read coverage distribution across the genome. The black line indicates 532× average base coverage across the genome.
	FIG 2. Maximum likelihood phylogeny of densoviruses (Akaike information criterion [AIC]; LG+G+I+F). The phylogenetic tree is based on an amino acid alignment performed by MUSCLE of the NS1 region spanning motif I of the RC endonuclease domain to motif C of the SF3 helicase domain (amino acid sequence length, 437.7 ± 50 [mean ± SD]). Branch supports were bootstrapped at 100 iterations and are shown as colored branches. Black branches indicate <80% support, blue branches indicate 80 to 90% support, and green branches indicate 90 to 100% support. Terminal node colors correspond to densovirus genera. Italicized names correspond to the animal genus and species from which the densovirus was isolated. AfaDV is indicated in boldface type with *.
	FIG 3. AfaDV prevalence among sea star populations along the North American Atlantic Coast (https://www.jing.fm/iclipt/u2q8u2q8i1w7t4o0/). A total of 134 animals from three species of sea stars were screened via qPCR or PCR for AfaDV. The year(s) of sampling is shown in parentheses. The prevalence for each species corresponds to the number of animals positive for AfaDV divided by the total number of animals listed next to each species.
	FIG 4. Viral load and tissue prevalence of AfaDV. (Left) Pearson’s correlation between viral load and animal length reported as total diameter. Colors correspond to sample types. Black dots represent cross-section samples. (Middle) Viral load comparison between tissue types. (Right) Prevalence of AfaDV among tissue types. ***, P ≤ 0.001; NS, no significance.

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