Japanese Tapeworm Infection

Japanese Tapeworm Infection

Digestive Health
Diseases & Conditions
Contributed byKrish Tangella MD, MBAOct 17, 2018

What are the other Names for this Condition? (Also known as/Synonyms)

  • Diphyllobothriasis due to Diphyllobothrium Nihonkaiense
  • Diphyllobothrium Nihonkaiense Infection
  • Infection by Japanese Tapeworm

What is Japanese Tapeworm Infection? (Definition/Background Information)

  • Japanese Tapeworm Infection is caused by the tapeworm species Diphyllobothrium nihonkaiense (or D. nihonkaiense). This species is different from Diphyllobothrium latum, which causes fish tapeworm infection
  • The parasites are flatworms that infect the intestinal tract of human beings. Individuals are affected by eating raw or uncooked fish that contain tapeworm cysts or larvae
  • Japanese Tapeworm Infection may cause abdominal pain, appetite loss, diarrhea or constipation, vomiting, nausea, and fatigue. The condition may be diagnosed by examining stool samples
  • The treatment of Japanese Tapeworm Infection involves the administration of oral and intravenous medications. The prognosis is generally good with no significant long-term complications being noted, if the condition is treated adequately

Who gets Japanese Tapeworm Infection? (Age and Sex Distribution)

  • Japanese Tapeworm Infection can affect individuals of all ages, races, and ethnic groups
  • Both male and female genders can be affected by the infection
  • D. nihonkaiense causing human infections was previously reported in Japan, South Korea, and the Pacific coast of Russia. The infection has also been reported in the United States

What are the Risk Factors for Japanese Tapeworm Infection? (Predisposing Factors)

The following are some known risk factors that can lead to Japanese Tapeworm Infection:

  • Consumption of raw or undercooked salmon (such as in sushi) harboring D. nihonkaiense cysts or larvae
  • Professional fishermen and their families, who primarily consume salmon as a main protein source, have a higher risk
  • Those who tend to taste undercooked or semi-cooked salmon, during its preparation
  • Any individual who consumes infected raw fish (such as sushi eaters in the Midwestern United States)

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Japanese Tapeworm Infection? (Etiology)

  • Japanese Tapeworm Infection is caused by the tapeworm species called Diphyllobothrium nihonkaiense
  • 4 species of salmon, mainly off the Pacific coast of United States, harbor this tapeworm. These include:
    • Chum salmon
    • Masu salmon
    • Pink salmon
    • Sockeye salmon
  • Humans are infected when they eat raw or undercooked fish that contains salmon tapeworm cysts, belonging to the species D. nihonkaiense
  • On consumption of the infected fish, the tapeworm larva begins to grow in the intestine. In about 3-6 weeks’ time, it grows to become an adult worm
  • Eggs are laid in each segment of the worm, which is then passed in the stool. Occasionally, whole or parts of the worm may be seen in the stool as well
  • The symptoms become apparent, approximately 10 days after consuming infected fish/food

What are the Signs and Symptoms of Japanese Tapeworm Infection?

Individuals with Japanese Tapeworm Infection may remain asymptomatic or may exhibit the following signs and symptoms: 

  • Abdominal pain
  • Loss of appetite, sudden weight loss
  • Diarrhea or constipation
  • Vomiting, nausea, and fatigue
  • Deficiency of vitamin B12
  • Anemia
  • Presence of worm eggs (or worm parts) in stool

How is Japanese Tapeworm Infection Diagnosed?

Japanese Tapeworm Infection is diagnosed using the following tools:

  • A thorough physical examination and an assessment of symptoms
  • An evaluation of medical history, with emphasis on eating habits
  • Stool test for the presence of eggs and parasites and/or tapeworm segments (proglottids) passed in the stool
  • Complete blood count (CBC) to check for anemia
  • Genetic testing of infecting tapeworm to differentiate between Diphyllobothrium latum (which causes fish tapeworm infection) and D. nihonkaiense (causing Japanese Tapeworm Infection)


  • The genetic testing may be performed for epidemiological reasons (to evaluate distribution patterns of the infection), since the test is not necessary for diagnostic purposes
  • Individuals with D. latum and D. nihonkaiense infections exhibit similar symptoms, and the treatment modalities are the same as well

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Japanese Tapeworm Infection?

The following are potential complications from Japanese Tapeworm Infection:

  • Vitamin B12 deficiency leading to megaloblastic anemia. It is a blood disorder that is characterized by anemia with larger than normal-sized red blood cells
  • Intestinal obstruction in extreme infections
  • If not treated properly, the infection can become chronic
  • Unintended weight loss
  • Stress

How is Japanese Tapeworm Infection Treated?

The treatment options for Japanese Tapeworm Infection are decided by a healthcare professional based on the type and severity of symptoms. The treatment measures may include the following:

  • Oral medications, which are anti-parasitic medicines
  • Medication to ease diarrhea and nausea
  • Vitamin B12 injections supplements to treat megaloblastic anemia

How can Japanese Tapeworm Infection be Prevented?

Japanese Tapeworm Infection may be prevented by considering the following measures:

  • Avoiding consumption of raw or undercooked salmon
  • Cooking fish to 145°F for 4-5 minutes to kill parasites (if any)
  • Washing hands properly after cleaning fish, before preparing food, and before eating
  • Freezing fish for storage; freezing at -4°F for 24 hours, can help kill the tapeworm eggs
  • Proper disposal of sewage (including fish wastes) can help bring down the risk of contracting Japanese Tapeworm Infection

What is the Prognosis of Japanese Tapeworm Infection? (Outcomes/Resolutions)

  • The prognosis of Japanese Tapeworm Infection is good, as the condition is treatable with medication
  • Generally, no lingering long-term effects of infection are noted, with early diagnosis and prompt treatment
  • However, without treatment, this infection can prolong and become chronic

Additional and Relevant Useful Information for Japanese Tapeworm Infection:

  • Diphyllobothriasis is an infection usually caused by the tapeworm Diphyllobothrium latum. Individuals are affected by eating raw or uncooked freshwater fish that contain tapeworm cysts

The following article link will help you understand diphyllobothriasis infection:


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Krish Tangella MD, MBA

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