Australians love their sushi and of seaweed-wrapped rolls and sashimi (slices of raw fish) per year.
But a story doing the rounds this week is enough to scare anyone off their raw salmon lunch. A presented to his local emergency department with abdominal cramps and bloody diarrhoea – caused by a 1.5-metre tapeworm. He seems to have contracted the parasite from raw sushi, which he ate most days.
Tapeworms are flat, segmented worms that live in the intestines of animals and humans.
The tapeworm the Californian man contracted was most likely fish tapeworm, or Diphyllobothrium latum. It is the found in humans – it can reach 10 metres in length and live for up to 20 years.
The life cycle of the fish tapeworm is complex. Eggs from infected animals and humans are into water, where they hatch. This first stage of larvae is ingested by crustaceans.
Fish are filleted, inspected and cut before sushi is made. Source: AAP
The larvae mature into a second stage in crustacaeans, which are then ingested by fish. When humans eat these fish in a raw or undercooked form, the larvae attach to the wall of the small intestine and can eventually develop into full-length tapeworms.
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Very often, fish tapeworms . When symptoms do arise, they are usually non-specific and can include diarrhoea, abdominal pain, vomiting and weight loss.
It’s really difficult to make the diagnosis of fish tapeworm simply by accounting for gastrointestinal symptoms. It’s only through careful history taking, including assessing a patient’s dietary history, that clinicians would even consider such a rare diagnosis.
Other parasites can be found in raw or undercooked seafood, including Anisakis.
The US Centers for Disease Control and Prevention has of fish tapeworms being found in Pacific Ocean salmon, including Alaskan wild salmon. This may be the source of the fish tapeworm found in the Californian man.
Other parasites can be found in raw or undercooked seafood, including Anisakis. Anisakis larvae than fish tapeworm (up to 3cm) but in the upper abdomen shortly after eating infected fish.
Thankfully, it is incredibly rare to contract a parasitic infection from eating sushi or sashimi in Australia. There has been only of infection by a close relative of fish tapeworm (Pacific broad tapeworm), and of Anisakis infection.
Raw fish sushi and sashimi in Australia predominantly contain salmon or tuna. Farmed salmon in Australia are raised on pelletised feeds and fish tapeworm or Anisakis larvae.
For tuna and other fish occasionally used in sushi, such as kingfish, there is an when they are first processed (during the gilling, gutting and filleting process). Fish buyers then actively look for cysts and larvae when inspecting tuna at fish auctions.
Very often, fish tapeworms do not cause symptoms. Source: Getty
Finally, when trained chefs prepare the sushi, they carefully slice the fish into thin portions (3-10mm), which increases the likelihood that they will detect any parasites.
When trained chefs prepare the sushi, they carefully slice the fish into thin portions, which increases the likelihood that they will detect any parasites.
You can also freeze your sushi before eating it. The US Food and Drug Administration raw or semi-raw seafood be blast frozen to −35℃ or below for 15 hours, or be conventionally frozen to −20℃ or below for 7 days, as this will kill any parasites in the fish.
Even though the risk of contracting parasites from eating sushi in Australia is very low, pregnant women and people with compromised immune systems should avoid raw or undercooked fish and seafood.
The good news is that even if you are unlucky enough to contract a tapeworm from eating sushi, it’s very treatable. A of the antiparasitic* drug praziquantel can effectively treat fish tapeworm.
