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Diphyllobothrium latum, Molecular Detection

Molecular testing for Diphyllobothrium latum is used for the diagnosis and laboratory documentation of diphyllobothriasis.

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Diphyllobothrium latum also called the “fish tapeworm” or the “broad tapeworm,” is transmitted to humans by the ingestion of fish that harbor infectious larvae of the genus Diphyllobothrium causing a wide-ranging spectrum of disease and severity. Freshwater fish serve as the primary epidemiological reservoir for Diphyllobothrium latum, while other Diphyllobothrium species originate from marine fishes. Thus, the fundamental risk factor is the consumption of raw freshwater or marine fish with human disease occurring after the maturation of larval stages of the tapeworm in the hosts’ intestines.

Diphyllobothrium latum is the longest human tapeworm and is typically 4 to 15 meters in length but can grow up to 25 meters within the human intestine. The rate of growth may exceed 22 cm/day, and they may remain active in the gut for over 20 years.  Diphyllobothrium latum is characterized by an anterior end called a scolex with attachment grooves on its dorsal and ventral surfaces. The body of the tapeworm is composed of many segments, each containing sets of male and female reproductive organs, allowing for its high fecundity.

Human infection with Diphyllobothrium latum (diphyllobothriasis) can range from an asymptomatic state to mild gastrointestinal symptoms to severe cases of anemia as well as luminal obstruction. Studies have shown that in patients infected with Diphyllobothrium latum 25% will manifest symptoms of abdominal pain, diarrhea, fatigue, headaches, or pernicious anemia. Diphyllobothriasis can affect any age group and gender, but the majority of identified cases were middle-aged men. Humans infected with Diphyllobothrium latum will begin to pass eggs in their stools on average 15 to 45 days after the ingestion of the larvae.

Laboratory workup may reveal peripheral eosinophilia and megaloblastic anemia along with vitamin B12 deficiency. In general, the diagnosis of Diphyllobothrium latum is from the presence of eggs or proglottids of the representative shape and structural characteristics in the patient’s stool sample.

Molecular methods using polymerase chain reaction (RT-PCR) for the laboratory diagnosis of Diphyllobothrium latum are the most reliable tool for the identification of the parasite.

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