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Something Fishy in Sushi? Increase in Incidence of Anisakiasis Parasite Infection in Western Culture


By: Heather Williams

Sushi has become increasingly popular in the United States.  Sushi bars and sushi based restaurants are popping up everywhere in metropolitan cities.  You can even find fresh made sushi in many grocery stores.  While this seemingly healthy meal sounds like a tasty alternative to traditional cuisine, raw food of any kind poses a health risk.  Raw and undercooked fish and squid are potential carriers of Anisakis, a parasitic nematode or worm.  Those who consume raw or undercooked infected fish may contract Anisakiasis.  According to the Centers for Disease Control and Prevention (CDC), Anisakiasis, also known as herring worm disease, is a parasitic disease caused by Anisakis worms attaching to the wall of the intestine, stomach, or esophagus.

When asked about the safety of eating raw fish, Lauri Wright, PhD, spokesperson for the Academy of Nutrition and Dietetics and assistant professor in public health at the University of South Florida said that it is best to avoid raw fish.  She explains that some individuals are at a higher risk for foodborne illness and could suffer severe and life-threatening illness from eating raw or undercooked fish or shellfish.  She explains that “there are no health benefits of consuming raw fish or sushi over cooked fish,” and it is safer to consume the fish at appropriately cooked temperatures.

Increased Reports of Anisaki Parasite Infection

Reports of Anisakiasis are increasing and being reported by the medical community.  In a recently published BMJ case report, a previously healthy man, age 32, presented symptoms of gastric pain, vomiting, and had a low grade fever.  He had been complaining of the symptoms for over a week.  His doctor opted for an upper gastrointestinal endoscopy after discovering he had recently consumed sushi.  What she found was a filiform parasite firmly attached to an area of swollen and hyperaemic (or inflammation with increased blood flow) mucosa.  Once the larvae were removed, the patient immediately felt better.  When the larvae were analyzed, it was determined to be Anisakis.

Symptoms may mimic other gastrointestinal issues making it more difficult for doctors to properly diagnose the infection.  This occurred in the case of a 51 year old woman who went to the doctor complaining of stomach pain, diarrhea, and vomiting.  He sister was recently diagnosed with duodenal adenocarcinoma, which produces similar symptoms.  Imaging was performed, which only revealed additional symptoms of thickened gastric antrum (lower part of the stomach) with enlarged lymph nodes in the area.  After endoscopy, the doctor was able to see three worms that had embedded in the stomach wall.  The larvae were identified as Anisakis.  “It’s ability to mimic peptic ulcer disease, chronic gastritis and malignancy necessitates broader diagnoses and lower thresholds for endoscopy”, explains Dr. Mohammad Qasim Khan of the Department of Internal Medicine at the University of Chicago.

Infection occurs very quickly.  In one case, a 65 year old man being treated for prostate cancer underwent a surveillance pelvic MRI, revealing a rectal tumor.  He subsequently had a colonoscopy to investigate.  While the colonoscopy found that he did have a tumor his rectum, the doctor also discovered a live worm attached to the tumor.  Analysis of the worm determined it was Anisakis and the patient had already contracted Anisakiasis.  After the procedure the patient said he had eaten a raw mackerel the night before for dinner.

How Does Someone Get Infected?

You may be asking yourself how someone might get infected with this parasite.  It starts as a series of events in the ocean food chain.  Often the parasite originates in a larger infected marine mammal like a sea lion or whale.  Eggs are released in the large animal’s waste, which become infective larvae.  The food chain continues to crustaceans (crabs, shrimp, barnacles, etc) eating the larvae and then squid or fish eating the crustaceans.  Eventually the infected fish or squid may make it to your sushi plate or other raw or undercooked fish dish in where you consume the larvae.  Once in your body, it invades your gastrointestinal tract making you ill.  Even when the parasite eventually dies, it will cause and inflamed mass in the area it has attached (your esophagus, stomach, or intestine for example).

If you are lucky, the movement of the worm causes a tingling sensation in your mouth or throat that will cause you to cough up or vomit, removing the parasite from your body.  Otherwise, the worm will need to be removed by endoscopy or surgery.

Not surprisingly, infection incidents are higher in Japan and other countries where raw seafood is more common.  However, cases of Anisakiasis are increasing in the United States, Europe, South America, and other areas due to the rise in popularity of sushi, sashimi, and ceviche.

How Will I Know If I Am Infected?

Initial symptoms of Anisakiasis include mild fever, abdominal pain, abdominal distention (swelling), nausea, diarrhea, blood and mucus in stool, and vomiting.  Some infected individuals may experience allergic reactions such as rash and itching, and more rare but serious symptoms such as anaphylaxis may occur.  If you need to seek medical care with these symptoms, be sure to disclose if you have eaten raw or undercooked fish or squid to your healthcare provider so they may approach diagnostic techniques that would identify if you have a parasitic infection as infection symptoms may mimic that of other gastric diseases.

How Do I Protect Myself and My Family?

The best way to protect yourself and your family is to completely avoid raw and undercooked food, including fish or squid.  The Food and Drug Administration (FDA) recommends cooking seafood to an internal temperature of at least 145ºF.

While freezing fish does not kill all parasite and both freezing and cooking will not remove or denature most toxins produced by parasites, the FDA has established the following food preparation guidelines in increase the safety of eating raw fish.

“Freeze Fish”

  • At -4ºF (-20ºC) or below for 7 days (total time, or
  • At -31ºF (-35ºC) or below until solid, and storing at -31ºF (-35ºC) or below for 15 hours, or
  • At -31ºF (-35ºC) or below until solid, and storing at -4ºF (-20ºC) or below for 24 hours.”

So next time you consider sushi for lunch or dinner, be sure to choose a restaurant known for quality sushi and ask about their fish preparation guidelines.  When in doubt, choose a cooked option.









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