A strain of the herpes virus has been found in several samples of Japanese oysters being farmed in the Wadden Sea, Nos television said on Tuesday.

The virus has been found in three out of five locations examined and there is a chance that 50% of the region’s young oysters could be infected, researcher Arjan Gittenberger of the Gimaris research institute told the broadcaster.

The virus was first identified in European oysters in 2008 and has had a serious effect on oyster beds in France, Britain and Ireland since then. It was first found in the Netherlands in 2010 in Zeeland oysters in the Oosterschelde estuary.

Gittenberger said it is unclear when the virus moved to the Wadden Sea and further research is now being carried out.

The virus is not dangerous to humans. Some researchers have linked its spread to global warming.