Diphyllobothrium tapeworm infection occurs when an animal is infected with cestodes (tapeworms), ribbon-like, segmented worms that are intestinal parasites. They totally lack a digestive system and do not ingest particular matter, but instead they absorb soluble nutrients. Cestodes cause injury to organisms by consuming the host's nutrients, by excreting toxic waste, and, in massive infestation, by causing mechanical blocking of the intestine.
The anterior end of the worm consists of a scolex, a structure with hooks and suckers that function to attach the worm to the intestinal wall. The body (strobila) is composed of many segments (proglottids). Each proglottid has a complete set of sexual organs, both male and female, that generate fertilized eggs. The mature, egg-filled proglottids are located at the end of the organism and can break off the chain and pass out of the body in the stool.
Diphyllobothriasis is a human disease caused by fish tapeworm Diphylobothrium latum (broad fish tapeworm) of the genus Diphyllobothrium. It represents the most important fish-borne zoonosis caused by tapeworms. Humans get infected by eating raw, insufficiently cooked, or marinated freshwater and marine fish. Increasing popularity of dishes based on raw fish meat, such as sushi, sashimi, carpaccio, or ceviche, significantly increases the risk of acquiring the parasite, even in the most developed countries. The adult Diphyllobothrium latum and Diphyllobothrium nihoncaense are the longest tapeworm species (2 to 12 meters in length) found in humans and can also infect dogs and cats. However, it probably does not attain this length in dogs and cats. Other animals that eat raw fish, including foxes, bears and seals can support maturation of the adult worm.
Most of the cases are asymptomatic, but in about one out of five cases, diarrhea, abdominal pain, or discomfort occurs. The main clinical manifestation is the observation of proglottids being passed in stools. The most important complications that result from human infection with the broad fish tapeworms stem from the ability of these helminths to rob the host of important vitamins and minerals. About 2% of infected individuals develop megaloblastic anemia and neurological symptoms of vitamin B12 deficiency, which include loss of vision. Infection with these tapeforms is treated with medical therapy and replacement complexes of vitamin B12 and folic acid.
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