Epidemiology
People at high risk for infection have traditionally been those who regularly consume raw fish. While people of any gender or age may fall sick, the majority of identified cases occurred in middle-aged men. Geographical distribution
Diphyllobothriasis occurs in areas where lakes and rivers coexist with human consumption of raw or undercooked freshwater fish. Such areas are found in Europe, newly independent states of the former Soviet Union, North America, Asia, Uganda, Peru (because of ceviche), and Chile. Many regional cuisines include raw or undercooked food, including sushi and sashimi in Japanese cuisine, carpaccio di persico in Italian, tartare maison in French-speaking populations, ceviche in Latin American cuisine and marinated herring in Scandinavia. With emigration and globalization, the practice of eating raw fish in these and other dishes has brought diphyllobothriasis to new parts of the world and created new endemic foci of disease.Infections in Europe and North America were traditionally associated with Jewish women due to the practice of tasting bits of uncooked fish during preparation of the gefilte fish dish, and also occurred in Scandinavian women for the same reason. Diphyllobothriasis was thus also referred to as the "Jewish housewifes disease" or the "Scandinavian housewifes disease". Japan
Diphyllobothriasis nihonkaiense was once endemic to coastal provinces of central and northern Japan, where salmon fisheries thrived. In recent decades, regions with endemic diphyllobothriasis nihonkaiense have disappeared from Japan, though cases continue to be reported among urbanites who consume sushi or sashimi.
Microscopy
Diagnosis is usually made by identifying proglottid segments, or characteristic eggs in the faeces. Eggs are usually numerous and can be demonstrated without concentration techniques. Morphologic comparison with other intestinal parasites may be employed as a further diagnostic approach.These simple diagnostic techniques are able to identify the nature of the infection to the genus level, which is usually sufficient in a clinical setting. Though it is difficult to identify the eggs or proglottids to the species level, the distinction is of little clinical importance because - like most adult tapeworms in the intestine - all members of the genus respond to the same treatments. Treatment may distort morphological features of expelled pathogen tissues and complicate subsequent morphological diagnosis attempts. Genetic identification
When the exact species need be determined (e.g. in epidemiological studies), restriction fragment length polymorphisms can be effectively used. PCR can be performed on samples of purified eggs, or on native fecal samples following sonication of the eggs to release their contents. Molecular identification is currently generally only used in research. Radiography
A potential diagnostic tool and treatment is the contrast medium gastrografin which, when introduced into the duodenum, allows both visualization of the parasite, and has also been shown to cause detachment and passing of the whole parasite. Prevention
Ingestion of raw freshwater fish should be avoided. Adequate cooking or freezing of freshwater fish will destroy the encysted fish tapeworm larvae. Fish that is thoroughly cooked, brined, or frozen at -10 °C for 24–48 hours can also be consumed without risk of D. latum infection.