Diphyllobothriasis is the infection caused by tapeworms of the Diphyllobothrium genus, commonly Diphyllobothrium latum
The subclass Cestoda of the class Cestoidea, under the phylum Platyhelminthes, includes 2 orders that infect humans: Cyclophyllidae and Pseudophyllidea. One of the main differentiating points between the genera of the 2 orders is that those of the first order typically have a scolex with 4 suckers, whereas those of the second have a scolex with 2 opposing sucking grooves. Another important point of differentiation is in Cyclophyllidae, there are 2 hosts in the life cycle, whereas in Pseudophyllidea, 3 are required. The order Pseudophyllidea includes the family Diphyllobothriidae, andDiphyllobothrium is one of the genera within this family. The species of this genus are all parasites of fish-eating vertebrates (hence the common use of the term fish tapeworm). This article focuses on the D latum, for which humans are the definitive host. A full-grown Diphyllobothrium worm can range from 1-15 m in length and is the longest human tapeworm. It consists of up to 3000-4000 proglottids. The scolex, as noted, has 2 sucking grooves, also called bothria. Proglottids are typically wider than they are long, which is why D latum is called the broad tapeworm.
Upon diagnosis, treatment is quite simple and effective. The standard treatment for diphyllobothriasis, as well as many other tapeworm infections is a single dose of praziquantel, 5–10 mg/kg orally once for both adults and children. An alternative treatment is niclosamide, 2 g orally once for adults or 50 mg/kg (max 2 g) for children. One should note that praziquantel is not FDA-approved for this indication and niclosamide is not available for human use in the United States. Reportedly, albendazole can also be effective. Another interesting potential diagnostic tool and treatment is the contrast medium, Gastrografin, introduced into the duodenum, which allows both visualization of the parasite, and has also been shown to cause detachment and passing of the whole worm. Avoid ingestion of raw freshwater fish. Adequate cooking or freezing of freshwater fish will kill the encysted fish tapeworm larvae. Also, because human feces is an important mechanism for spreading eggs, proper disposal of sewage can cut down on infection of fish and thus of humans.