- The French Research Institute for the Exploitation of the Sea published this Monday the results of analyzes carried out on 21 samples of oysters and mussels taken from various locations on the French coast.
- Ifremer wanted to check if there were traces of SARS-Cov-2 on these shells, real seawater filters. In which case, we would have proven the passage of the virus, from our wastewater to the coast.
- The first results are reassuring: no trace of SARS-CoV-2 was found. However, Ifremer launched a second wave of analysis of samples, this time taken during the deconfinement period. What to change everything?
Two samples of mussels and nineteen hollow oysters from the three French maritime façades. Three on the Normandy coast, eight on the Brittany coast, eight on the Atlantic coast, and three on the Mediterranean coast. In mid-April, the French Research Institute for the Exploitation of the Sea (Ifremer) implemented an operation to collect shellfish samples, in order to check whether traces of SARS-CoV-2, the virus responsible of the Covid-19 pandemic, could be detected there.
Result? Of these 21 samples, none showed any trace of SARS-CoV-2. "Good news," says Soizick Le Guyader, head of the Nantes laboratory "Health, environment and microbiology" (LSEM) at Ifremer.
Seashells, mirror of discards at sea?
The issue is not trivial in any case. Between the end of December and the first weeks of January, around twenty shellfish production sites, from Normandy to Hérault, had been the subject of prefectural health closure orders after contamination of oysters with norovirus, a virus human-transmitted gastroenteritis. The oyster farmers then pointed out the responsibility for the treatment plants and the shortcomings in the treatment of wastewater. "Discharges are not always well treated by treatment plants and the virus is found in the maritime environment", denounced Philippe Le Gal, chairman of the South Brittany shellfish farming committee, interviewed by AFP.
Once at sea, these organic matters, potentially loaded with virus, are filtered by shellfish, for which it is a source of nutrient. This is how a virus can get from our toilet to the seafood.
If this path is possible for gastroenteritis viruses, is it also possible for SARS-CoV2? "During an epidemic of gastroenteritis in a population, we know that we can find impressive quantities of norovirus in wastewater, because they are transmitted through the digestive tract, and those who are sick of it literally empty themselves in the toilets, if you allow me the expression, ”recalls Soizick Le Guyader.
Detected in wastewater, but not yet at sea?
For SARS-COV2, it's not the same story. It is already a respiratory virus, and it also consists of an envelope which in theory makes it more fragile and therefore less resistant in water. But this virus keeps its share of mystery for the scientific community. In regions strongly affected by the epidemic, notably in Paris and in the Grand-Est region, several analyzes of wastewater revealed the presence of the SARS-CoV-2 genome, with quantities correlated with the number of people hospitalized. "We were a little surprised to see that SARS-CoV2 was excreted in the stools of patients hospitalized at concentrations high enough for a respiratory virus", continues Soizick Le Guyader.
The first analyzes of Ifremer tend to show that the SARS-CoV2 virus does not reach shells. "The samples, however, come from areas that are known to be contaminated by human waste and of the 21 analyzed, six showed traces of norovirus," said the LSEM official.
Reassuring for lovers of seafood and swimming?
Reassuring for lovers of seafood as for those swimming in the sea? Soizick Le Guyader is tempted to say "yes", especially since "the bathing and shellfish growing areas have a much better micro-biological quality than where the samples were taken and are very regulated on this point", recalls she.
However, this is only a first result, and there is no indication that it will be confirmed in later studies. Ifremer is currently launching the second wave of analysis. "This time, the samples will be taken during the deconfinement period, at a time so there will theoretically be more people on our shores," says Soizick Le Guyader. "And if we find it, nothing says that this virus is still infectious for humans," insists the director of LSEM. It will not be easy to demonstrate. "
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Analysis of samples in treatment plants
In addition to its analyzes of shellfish, LSEM has implemented a sampling plan for three wastewater treatment plants in the Great West: two from an urban area and one from a coastal area. Still with the aim of looking for the SARS-CoV2 genome, this time, directly in the wastewater. The results are expected in the coming days, announces Soizick Le Guyader.
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