The Dutch food safety body NVWA is warning that any shell fish picked up from the Westerschelde estuary in Zeeland run the risk of being contaminated with the polio virus.

Cockles, mussels and oysters collected from the estuary must be boiled for at least 90 seconds, the NVWA advises.

The source of the contamination is in Rixensart, south of Brussels, where 45 litres of water contaminated with the polio virus leaked from the GlaxoSmithKline factory into the river Laan.

That water has now reached the Westerschelde, the NVWA says, adding that it is now so diluted there is no risk from swimming.

The risk of catching polio from eating the shell fish is very small but few people around the Westerschelde have been vaccinated against the virus, the NVWA says.