Fish tapeworm infection
Fish tapeworm infection is an intestinal infection with a parasite found in fish.
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:
After a person has eaten infected fish, the 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 nutrition from 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:
Exams and Tests
People who are infected sometimes pass segments of worm in their stools. These segments can be seen in the stool.
Tests may include:
You will receive medicines to fight the parasites. You take these medicines by mouth, usually in a single dose.
The drug of choice for tapeworm infections is praziquantel. Niclosamide can also be used. If needed, your health care provider will prescribe vitamin B12 injections or supplements to treat vitamin B12 deficiency and anemia.
Fish tapeworms can be removed with a single treatment dose. There are no lasting effects.
Untreated, fish tapeworm infection may cause the following:
When to Contact a Medical Professional
Call your provider if:
Measures you can take to prevent tapeworm infection include:
King CH, Fairley JK. Tapeworms (cestodes). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Updated Edition. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 291.
White AC, Brunetti E. Cestodes. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 354.
Review Date: 9/27/2017
Reviewed By: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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