Detection of SARS-CoV-2 RNA in bivalve mollusks and marine sediments

Abstract

The presence of SARS-CoV-2 in wastewater pose the question of whether this new pandemic virus could be released into watercourses and potentially continue to finally reach coastal waters. In this study, we employed two bivalve molluscan species from the genus Ruditapes as sentinel organisms to investigate the presence of SARS-CoV-2 signals in the marine coastal environment. Estuarine sediments from the natural clam banks were also analyzed. Viral RNA was detected by RT-qPCR, targeting IP4, E and N1 genomic regions. Positive samples were also subjected to a PMAxx-triton viability RT-qPCR assay in order to discriminate between intact and altered capsids, obtaining indirect information about the viability of the virus. SARS-CoV-2 RNA traces were detected in 9/12 clam samples by RT-qPCR, from which 4 were positive for two different target regions. Viral quantification ranged from <LoQ to 4.48 Log genomic copies/g of digestive tissue. Regarding the sediment samples, 3/12 were positive by RT-qPCR, but only IP4 region was successfully amplificated. Quantification values for sediment samples ranged from <LoQ to 3.60 Log genomic copies/g of sediment. RNA signals disappeared in the PMAxx-triton viability RT-qPCR assay, indicating non-infectious potential. In addition, the recently discovered human-specific gut associated bacteriophage crAssphage was also quantified as a biomarker for the presence of human-derived wastewater contamination on the study area. CrAssphage was detected in 100% of both types of samples with quantification values ranging from <LoQ to 5.94 LOG gc/g digestive tissue and from <LoQ to 4.71 LOG gc/g sediment. Statistical analysis also showed that quantification levels for the crAssphage in clams are significantly higher than in sediments. These findings represent the first detection of SARS-CoV-2 RNA in the marine environment, demonstrating that it can reach these habitats and make contact with the marine life.

First evidence of SARS-CoV-2 genome detection in zebra mussel (Dreissena polymorpha)

“…Also in the marine environment, the Ruditapes genus had shown its efficiency in accumulating the SARS-CoV-2 genome in their digestive tissues (Polo et al, 2021). The authors of this study concluded that mollusc bivalves can be used as biomonitoring tools for various anthropogenic contaminants, including the SARS-CoV-2 virus.…”

“…or in countries whose water treatment structures are still underdeveloped. As announced by several recent studies, the bivalve taxon represents a complementarity, even a more than plausible alternative for the detection of viruses in the environment (Capizzi-Banas et al, 2021;Desdouits et al, 2021;La Rosa et al, 2021;Polo et al, 2021). Various fields of application can therefore be envisaged, such as 486 environmental biomonitoring for health purposes.…”

“…Nevertheless, some studies have detected SARS-CoV-2 genomes in treated wastewaters at wastewater treatment plants in France and Germany (Westhaus et al, 2021;Wurtzer et al, 2020b). This virus can also be detected in rivers in many developing countries, with rudimentary or in the absence of water treatment systems (Guerrero-Latorre et al, 2020), but also in developed countries (Polo et al, 2021;Rimoldi et al, 2020). However, there is still little knowledge concerning the survival of infectious SARS-CoV-2 in this aquatic environment.…”

“…Bivalve molluscans can indicate bacterial, protozoan or even viral contamination (Bighiu et al, 2019;Capizzi-Banas et al, 2021;Kerambrun et al, 2016;La Rosa et al, 2021). The high filtration capacity of bivalves allows them to filter large volumes of water (Palos Ladeiro et al, 2018;Polo et al, 2021). These invertebrate organisms can therefore be exposed to a panel of contaminants potentially more representative of their environment than that found in a water sample.…”

Environmental stability of porcine respiratory coronavirus in aquatic environments

“…With that in mind, our results support the consensus that a significant accumulation of terrestrial CoVs in the coastal environment is unlikely. Attempts to find infectious SARS-CoV-2 in seawater have so far failed [51,52]. More research is, however, still needed to understand the environmental fate of CoVs.…”