Plenty of people love sushi – this artistic, often brightly-colored food has been enjoyed by people the world over for hundreds of years. However, there are some dangers to eating sushi that contains raw fish. Specifically, certain species of worms can stay alive in sushi and infest the person who eats it. Some worm species can get into the eyes and central nervous system, creating serious complications.

What Kinds of Worms Are Found in Sushi?

Nematodes – Nematodes are worms that are usually round, and an infestation with them contracted from eating raw or undercooked saltwater fish is known as anisakiasis. These worms find their way into sushi when marine mammal feces enter the ocean. These feces often contain the eggs of these worms, which hatch and become larvae. The larvae are eaten by fish and other animals in the ocean.

When the fish that has consumed the nematodes are caught and made into sushi, the worms don’t die. They remain in the sushi until they are ingested by the consumer. In some cases, people have reported a “tingling” feeling after consuming sushi. This feeling is actually a worm, and some people who have experienced this feeling have successfully extricated the worm from their mouth.

The reason that this type of worm is found almost exclusively in sushi is because, if the meat it’s in is cooked thoroughly, the worm dies. Refrigeration won’t kill a marine parasite though the CDC recommends rigorous freezing and thawing procedures to minimize your risk of consuming a marine parasite.

The worms responsible for anisakiasis primarily affect the digestive tract, and they can attach to the esophagus, stomach, or intestines. The larva will grow into an adult worm (usually about an inch long). When the worm dies, it creates an inflamed mass in the body that may cause complications.

Not all people who have anisakiasis get the “tingly” feeling after eating uncooked fish. Symptoms of anisakiasis include abdominal pain, diarrhea, and low-grade fever. Those with an allergy may present with an allergic reaction that is occasionally as severe as anaphylaxis.

What do you do if you suspect anisakiasis? It’s a good idea to see a doctor. If the doctor suspects you may have anisakiasis (which is much more likely if you regularly consume uncooked seafood), he or she may perform an endoscopy or even do surgery if the worm has embedded in the body.

Tapeworms – While the worms causing anisakiasis are primarily found in saltwater fish, tapeworms are usually found in freshwater fish (or fish who spend a part of their lives in freshwater). Salmon are a common carrier.

Tapeworms, like the nematodes responsible for anisakiasis, generally stay in the digestive tract. In many cases, a person with a tapeworm infestation from sushi will not have symptoms. However, an infected person may experience diarrhea, general discomfort, and weight loss. In extreme cases, the worms may cause an intestinal obstruction.

Gnathostomiasis: the Most Dangerous

Anisakiasis and tapeworm infestations can be inconvenient and painful, and they may cause the sufferer to need surgery. However, gnathostomiasis, or an infection with a worm (nematode) from the genus gnathosoma, is often much worse. These parasitic worms are most commonly seen in southeast Asia and parts of Africa, but they are rare in the Americas. These worms resemble small lampreys, and they are contracted much like anisakiasis is.

Though eating uncooked seafood is a common way to contract a gnathostoma worm, eating undercooked or uncooked freshwater animals (including birds who drink from freshwater) can put a person at risk. And while the worms responsible for anisakiasis generally are confined to the digestive tract, these worms can travel into many areas of the body.

Most commonly, gnathosoma worms are seen as small swellings under the skin. These swellings, unlike most skin bumps, move. This is because the worm moves right beneath the skin. If you do see a moving swelling, it’s imperative that you see a doctor immediately, as many of these worms move deeper into the body.

A gnathosoma worm may work its way into the liver and into the central nervous system and eyes. Though the worm is not poisonous, it can cause pain, paralysis, coma, and death. This is because it travels along nerves, causing excruciating pain. If the worm gets to the eyes, it can cause permanent blindness.

The most common signs you have worms inside are:

  • diarrhea
  • vomiting
  • fever
  • nausea
  • malaise
  • abdominal or right upper quadrant pain
  • sudden weight loss

So What Can You Do About It?
The CDC recommends avoiding uncooked or undercooked fish. If you are very worried about worms but still want to enjoy sushi, most restaurants offer fully-cooked rolls in addition to raw rolls. If you do eat raw or undercooked fish, however, it’s important to be vigilant.

For instance, you will likely be able to tell if you have worms approaching your brain if you suffer severe, unexplained nerve pain. In order to avoid this, though, monitor your skin closely, especially after eating raw fish. If you see a bump, watch to ensure it isn’t moving. If it moves – or if you experience abdominal pain or any of the other symptoms of an infestation, visit a doctor to avoid more serious complications.

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