Cestoda of Fish

Scientific classification Kingdom: Animalia Phylum: Platyhelminthes Class: Cestoda Subclass: Eucestoda Order: Pseudophyllidea Family: Diphyllobothriidae Genus: Diphyllobothrium Species: D. latum

Diphyllobothrium latum Morphology Disease. diphyllobothriasis It is commonly known as( broad tapeworm) or( fish tapeworm) Occurs in the small intestine of fish eating mammals such as man ,dog, cat, pig polar bear in many parts of the world.  Is found in and around freshwater lakes and streams. Each stage inhabits a different habitat. The eggs inhabit fecal matter from the definitive host, the larvae live first in a copepod and then in the flesh of fish, and the adults inhabit mammalain  intestines . The adult Diphyllobothrium latum may reach up to 2-12 meters, increasing throughout its life. These whitish/yellow worms are dorso-ventrally flattened, and much more narrow than they are long. They have no oral opening, thus feeding through absorption.

The finger-shaped or (spoon-shaped) scolex has no hooks, and narrow weakly-muscular grooves (bothria) run longitudinally along the body. Diphyllobothrium latum is hermaphroditic, and capable of self- fertilization ,carrying both sets of sex organs .In each proglottid, testes and vitelline follicles are found . Ovary is a bilobed in the posterior part of the proglottids . The uterus is rosette–shape with (4-8 loops), extending from the ovary to the uterine pore on the mid ventral surface of the segment, through which the mature proglottids (the term for a complete set of sex organs) release the eggs . The eggs are golden brown ,operculated , oval with rounded shape and average 60 ×42 µm .

Life cycle

Life cycle 1 : Immature D. latum eggs are passed in the feces of the human host. 2. These eggs then complete development in fresh water. Life Cycle continues in crustaceans: 3. Small, ciliated coracidium larvae hatch from mature eggs, and swim about until ingested by crustaceans. 4. The second larval stage is completed in the crustacean with the development of the procercoid. Life Cycle then moves to fish: 5. Infected crustaceans are the ingested by small freshwater fish. The procercoid larva are then released from the crustacean into the fish. The larvae continue to develop in the flesh of the fish, developing into the plerocercoid stage, which is the infective stage for humans. If humans ingest this fish, they will become infected. However, the fish ingesting an infected crustacean is small and usually not prey for any mammals.

6. Thus, a larger predator fish ingests the smaller infected fish 6. Thus, a larger predator fish ingests the smaller infected fish. The plerocercoid may infect the larger fish, but will not continue to grow as the fish is only a transport host. Life Cycle completes itself in Human or other suitable Mammal: 7. Human (or other mammal) ingests raw or undercooked infected fish. 8. Plerocerciod larva is not digested, but instead remains in the small intestine of its new host and grows to adulthood. 9. Proglottids release immature eggs, completing the cycle.

pathology and clinical symptoms pathology and clinical symptoms. Symptoms depend on the mass of the worm, amount of its by-products absorbed by the host, and the host's susceptibility to the foreign substances. Some infected people show no symptoms. There may be intestinal obstruction, diarrhea, abdominal pain, or anemia. D.latum absorbs ten to fifty times vitamins B12 . In fish plerocercoids can cause much damage with adhesion , sterility and even death .

Diagnosis.  Diagnosis is based on the recovery of the characteristic eggs or proglottids. Proglottids are often passed in chains in a few cm or longer. The overall proglottid morphology with the rosette-shaped uterus structure also facilitates identification .

TREATMENT  Drug of choice:  Praziquantel Alternative:  Niclosamide Additionally, Vitamin B12 may be needed to correct a deficiency caused by infection. Prevention Tapeworm infections are very difficult to cure completely Infection by Diphyllobothrium latum may be prevented by not eating raw or undercooked fish and salmon.  and freezing for 24-48 hours at -18° C.

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