Foto: NIFES

NIFES scientists were surprised to find the parasite Chinese liver fluke in farmed Pangasius in Vietnam. At worst, the parasite can cause serious liver disease and cancer if the actual seafood is eaten raw, without prior freezing or properly heating.

‘We did not expect to find Chinese liver fluke. This is a new parasite species for the Mekong Delta,’ NIFES scientist Arne Levsen says.

Together with Vietnamese scientists, he was in charge of a parasitological study that analysed farmed Pangasius in Vietnam.

Can cause serious illness

The Chinese liver fluke is a dangerous parasite that can be transferred to people through consumption of raw or only lightly processed freshwater fish from China and Southeast Asia. In the human body, Chinese liver fluke thrives in the gall bladder and the bile ducts of the liver.

‘Serious infections with hundreds of flukes can cause inflammation and blockage of the bile ducts, often with jaundice-like symptoms. In a worst-case scenario, the parasite can even cause liver cancer,’ says Levsen.

Chinese liver fluke is one of the most widespread food-borne flukes in Asia. According to the World Health Organization, 30 million people are infected with this parasite globally.

Be cautious when eating local seafood

Due to this finding, Levsen encourages tourists visiting Vietnam and Southeast Asia to avoid local, only lightly processed fish dishes. Proper heating is required to kill the parasites.

Europe imports regularly large quantities of Pangasius.

‘If you do not know if the seafood you’re offered has undergone proper heat treatment, don’t eat it. This goes for all seafood, including crabs and prawns, which may contain other parasites that can be dangerous,’ he says.

Imported to Europe

Europe imports regularly large quantities of Pangasius, where it is often sold as ‘whitefish’ or ‘sole’ to lend it a more exclusive flair.

‘All Pangasius bound for Europe are visually examined for parasites, but Chinese liver fluke is impossible to spot with the naked eye,’ says Levsen.

However, since Pangasius is frozen when it is imported to Europe, the parasite is not a food safety concern. Parasites die when frozen.

‘But should we ever start to import fresh Pangasius, there would be reason for concern,’ he says.

On assignment of the Norwegian Food Safety Authority, NIFES analyses annually various samples of seafood imports to Norway.

Where does the fluke come from?

Vietnamese Pangasius was examined as part of a large EU project known under the striking acronym PARASITE. In addition to analysing 865 farmed fish, the scientists also checked 130 wild Pangasius from basically the same area for parasites.

But no Chinese liver flukes were found in the wild fish. So where does the parasite come from?

‘We’re now trying to find that out,’ says Levsen.

Our present working hypothesis is that the parasite was brought along with broodstock from areas where the parasite occurs naturally.

‘It probably originates in other regions of Southeast Asia such as Thailand or South China. We are now comparing various genes to check if there are any genetic footprints that enable us to trace the flukes back to their area of origin,’ the NIFES scientist says.

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