A warning about the dangers of eating raw or lightly cooked seafood was issued today after cholera bugs were found in Norwegian mussels.

The Vibrio cholerae bacteria did not include dangerous strains of the sort that cause deadly epidemics.

But other related bacteria present in the same samples produced toxins that lead to diarrhoea.

Vibrio bacteria were also found in Norwegian inshore seawater, posing a greater risk of illness through swimming or handling fish.

All the bugs were capable of producing serious wound infections, especially in people with weak immune systems.

The bacteria, V cholerae, V parahaemolyticus, and V vulnificus were previously unknown in Norway.

V parahaemolyticus can be found in sushi and is one of the most common causes of food poisoning. V vulnificus is associated with oysters.

All three vibrio bugs were discovered in Norwegian mussels and seawater by Anette Bauer Ellingsen of the Norwegian School of Veterinary Science.

A statement from the school said: "The study showed that the danger of food poisoning posed by vibrios in Norwegian food products is extremely small.

"Nevertheless, toxin-producing V parahaemolyticus was demonstrated, so one should be careful when eating raw or lightly-cooked seafood, for example oysters."