SEAFOOD & RAW SEAFOOD ISSUES
Raw fish and seafood do not present the same potential hazards as raw meats, but they can still cause problems with health and safety. Some are natural toxins acquired by the animal from their own foods.
But let's first look at the microbiological hazards first.
Does sashimi (raw fish) carry parasites? The possible parasites from sashimi are zero where the fish has been commercially frozen. Where the fish has NOT been frozen, such as in much of Japan, two types of parasite are possible. Marine (salt-water) fish can be infested with small roundworms, typically Anisakis or Phocanema. These are incapable of completing their life cycle in the human (they need a marine mammal such as seal or walrus, and then herring, cod, haddock, etc.). But in the meantime, they can puncture the epithelial lining of the alimentary canal, and give rise to pain and sometimes peritonitis. (“False appendicitis” is one of the common manifestations of Anisakiasis in Japan).
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Fresh-water species can contain the cyst of the fish tapeworm, Diphyllobothrium latum. Realistically, with sashimi, this is limited to salmon (which of course as an “anadromous” species, spends a portion of its life in fresh AND salt water). This cyst, if viable, can develop into a tapeworm in the human that can extent the full length of the intestine (10 metres). Both are killed by freezing.
How likely? In North America and most of Europe, frozen fish are used for sashimi, hence no viable parasites. Eat sashimi in Japan, or prepare do-it-yourself ceviche or ‘poke', and the risks increase to some extent. But Anisakiasis is self-limited, and Diphyllobothriasis is rare and not a threat to a well-fed human.
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Raw shellfish increasingly are found to be the vehicles for Vibrio species as well as norovirus infections. It’s long past time to stop eating raw oysters, especially as the range of Vibrio infections is increasing with climate change.
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Never eat snails or slugs raw (even by accident on salads in the tropics). They carry parasites such as the rat lung worm, which can be fatal to humans.
Crabs (freshwater or saltwater) should only be eaten after cooking .
This applies especially to the famous "Chinese mitten crab"
(Eriocheir sinensis) 大閘蟹, 大闸蟹, dàzháxiè, also known as the
Shanghai hairy crab (上海毛蟹, ShànghÇŽi máoxiè). This crab is host
to the Paragonimus liver fluke in humans.
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