Broad fish tapeworm

Diphyllobothrium latum

ORDER

Pseudophyllidea FAMILY

Diphyllobothriidae TAXONOMY

Taenia lata Linnaeus, 1758, type locality unknown.

OTHER COMMON NAMES German: Fischbandwurm.

PHYSICAL CHARACTERISTICS

Polyzoic. Strobila with length about 30 ft (9 m) (there are data about specimens reaching up to 66 ft [20 m]), consisting of 3,000-4,000 proglottides. Scolex finger-shaped, with two both-ria. Uterus rosette-shaped in gravid proglottides.

DISTRIBUTION

Scandinavia, Baltic States, Russia, United States and Canada (Great Lakes area, Pacific Coast, Arctic), Ireland, Japan, around some lakes and large rivers in Africa, and South America.

HABITAT

Adults are common intestinal parasites of fish-eating mammals (dogs, cats, bears, seals, humans). Larvae develop in crustaceans (first intermediate hosts) and fishes (second intermediate hosts). The macrohabitats include rivers and freshwater lakes.

South American Parasite Fish

I Phyllobothrium squali I Proteocephalus longicollis

Biological Reproduction

FEEDING ECOLOGY AND DIET

Internal parasite absorbing nutrients through the tegument.

BEHAVIOR Nothing is known.

REPRODUCTIVE BIOLOGY

As almost all cestodes, this species is hermaphroditic. Eggs are released through the uterine pore and pass into the environment with feces of the host. The embryo encompassed in the egg needs one or several weeks (depending on the temperature) to become infective. The fully developed embryo (known as coracidium) hatches from the egg in water. It is covered by ciliated epidermis and can swim several hours until being eaten by a copepod crustacean (first intermediate host). In the intestine of the copepod, the coracidium loses its ciliated cover and penetrates into the body cavity. There, the embryo feeds on the nutrients contained in the hemolymph. For about 20-25 days, it turns into an elongate larva (procercoid, up to 0.0197 in [500 pm] long) possessing a cercomer at its posterior end. The procercoid is pathogenic for the copepod in terms of interfering with its motility and thus turning it into an easy prey for fishes. When the infected copepod is eaten by a fish (second intermediate host), the procercoid migrates from the intestine into the body musculature and turns into the next larval stage (plerocercoid). The predation of infected fishes, or even eating undercooked fish dishes in a restaurant, is the way of the transmission of the plerocercoid (from several millimeters to a few centimeters long) to the final host. In the host's intestine, the worm grows and becomes mature for some two weeks.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

This species is of great medical importance. The disease caused by it is named diphyllobothriasis. Among the most widespread parasitic diseases caused by tapeworms, it is ranked fourth. Its symptoms are diarrhea, abdominal discomfort, and weakness, in some cases anemia. The contemporary drug treatment is very efficient. ♦

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