Fish Tapeworm Infection Overview
Learn About Fish Tapeworm Infection
Fish tapeworm infection is an intestinal infection with a parasite found in fish.
Diphyllobothriasis
The fish tapeworm (Diphyllobothrium latum) is the largest parasite that infects humans. Humans become infected when they eat raw or undercooked freshwater fish that contain fish tapeworm cysts.
The infection is seen in many areas where humans eat uncooked or undercooked freshwater fish from rivers or lakes, including:
- Africa
- Eastern Europe
- North and South America
- Scandinavia
- Some Asian countries
After a person has eaten infected fish, the worm larva begins to grow in the intestine. Larvae are fully grown in 3 to 6 weeks. The adult worm, which is segmented, attaches to the wall of the intestine. The tapeworm may reach a length of 30 feet (9 meters). Eggs are formed in each segment of the worm and are passed in the stool. Sometimes, parts of the worm may also be passed in the stool.
The tapeworm absorbs the nutrients from the food that the infected person eats. This may lead to vitamin B12 deficiency and anemia.
Most people who are infected have no symptoms. If symptoms do occur, they may include:
- Abdominal discomfort or pain
- Diarrhea
- Weakness
- Weight loss
You will receive medicines to fight the parasites. You take these medicines by mouth, usually in a single dose.
The medicine of choice for tapeworm infections is praziquantel. If needed, your health care provider will prescribe vitamin B12 injections or supplements to treat vitamin B12 deficiency and anemia.
Roman Kuchta practices in Ceske Budejovice, Czech Republic. Mr. Kuchta is rated as an Elite expert by MediFind in the treatment of Fish Tapeworm Infection. His top areas of expertise are Fish Tapeworm Infection, Helminthiasis, Secernentea Infections, and Distomatosis.
Hiroshi Yamasaki practices in Tokyo, Japan. Mr. Yamasaki is rated as an Elite expert by MediFind in the treatment of Fish Tapeworm Infection. His top areas of expertise are Fish Tapeworm Infection, Helminthiasis, Distomatosis, and Amebic Liver Abscess.
Tomas Scholz practices in Ceske Budejovice, Czech Republic. Mr. Scholz is rated as an Elite expert by MediFind in the treatment of Fish Tapeworm Infection. His top areas of expertise are Fish Tapeworm Infection, Helminthiasis, Distomatosis, and Secernentea Infections.
Fish tapeworms can be treated with a single treatment dose. There are no lasting effects.
Untreated, fish tapeworm infection may cause the following:
- Anemia caused by vitamin B12 deficiency (megaloblastic anemia)
- Intestinal blockage (rare)
Contact your provider if:
- You have noticed a worm or segments of a worm in your stool
- You have symptoms of anemia
- Any family members are diagnosed with a fish tapeworm infection
Measures you can take to prevent tapeworm infection include:
- Do not eat raw or undercooked fish.
- Cook fish at 145°F (63°C) for at least 4 minutes. Use a food thermometer to measure the thickest part of the fish.
- Freeze fish at -4°F (-20°C) or below for 7 days, or at -31°F (-35°C) or below for 15 hours.
Published Date: August 05, 2025
Published By: Jatin M. Vyas, MD, PhD, Roy and Diana Vagelos Professor in Medicine, Columbia University Vagelos College of Physicians and Surgeons, Division of Infectious Diseases, Department of Medicine, New York, NY. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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Fischer PR, White AC. Adult tapeworm infections. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 348.
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