Shellfish bought from stores in Glasgow and the east coast have been found to contain the hepatitis E virus (HEV).
A team from Glasgow Caledonian University (GCU) found traces of the virus in eight blue mussels and one oyster after testing 310 samples.
It is the first time HEV has been found in commercially sold shellfish harvested from Scottish waters.
Hepatitis E is generally a mild disease but can be more serious for pregnant women.
The infection usually manifests itself in flu-like symptoms, jaundice, tiredness, fever, and vomiting and can also cause problems for those contracting it through blood transfusions.
'Food processing'
The shellfish tested in the study were bought from four supermarkets in the Glasgow area and a fishmonger on the east coast, although the individual outlets have not been named.
Researchers are now calling for further UK studies into food-borne transmission of the infection.
The most recent figures from 2016 show the number of laboratory-diagnosed cases of HEV in Scotland increased to 206 from just 13 in 2011.
Previous cases of HEV were linked to contaminated pork meat and soft fruit in Europe.
Prof Linda Scobie, principal investigator of the GCU study, said: "We don't know at what point in the food processing chain this contamination occurred.
"There are significant gaps in our knowledge with HEV in the UK, we don't know how much virus is required to cause infection, unlike the norovirus where you only need a few particles to cause acute illness.
"What we do know is more people are being diagnosed and if they have particular medical conditions then they are at risk of becoming very ill."
Unlike oysters, which are traditionally eaten raw, mussels are less likely to pose a risk of HEV infection to consumers because they are normally cooked before being eaten.
The authors, writing in the academic journal Food and Environmental Virology, said: "The present study is the first to demonstrate the occurrence of HEV in commercially harvested Scottish mussels sold at retail, albeit at low levels, 2.9%."
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