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.
latum competes with the host for vitamin B12 absorption, absorbing some 80% of dietary intake and causing deficiency and megaloblastic anaemia in some 40% of cases. Vitamin B12 uptake is enabled by the position of the parasite which usually lodges in the jejunum. Vitamin B12 deficiency is - according to research - conversely seldom seen in D. pacificum infection. Gastrointestinal obstructions
Rarely, massive infections may result in intestinal obstruction. Migration of proglottids can cause cholecystitis or cholangitis. Cause
Diphyllobothriasis is caused by infection by several species of the Diphyllobothrium genus. Transmission
Humans are one of the definitive hosts of Diphyllobothrium tapeworms, along with other carnivores; fish-eating mammals (including canids, felids, and bears), marine mammals (dolphins, porpoises, and whales), and (a few) birds (e.g. gulls) may also serve as definitive hosts.Definitive hosts release eggs in faeces; the eggs then mature in ~18–20 days if under favourable conditions. Crustaceans serve as the first intermediate hosts, and Diphyllobothrium larvae develop. The larvae are released when crustaceans are consumed by predators, which serve as second intermediate hosts (these are mostly small fish). Larvae move into deeper tissues in the second intermediate host. Second intermediate hosts do not serve as an important source of infection of humans as these are not regularly consumed raw.