Diphyllobothriasis

• Diphyllobothriasis is an infection that is caused by the tapeworm diphyllobothrium latum and related species;
• It is transmitted via consumption of raw or undercooked fish, and symptoms include abdominal discomfort, diarrhea, vomiting, fatigue, weight loss, and vitamin b12 deficiency.

Scolex of Dibothriocephalus latus

• Diphyllobothrium latum and related species (the fish or broad tapeworm), the largest tapeworms that can infect people, can grow up to 30 feet long.

• While most infections are asymptomatic, complications include intestinal obstruction and gall bladder disease caused by migration of proglottids.
• Diagnosis is made by identification of eggs or segments of the tapeworm in a stool sample with a microscope.
• Safe and effective medications are available to treat Diphyllobothrium.
• Infections are acquired by eating raw or undercooked fish, usually from the Northern Hemisphere (Europe, newly independent states of the Former Soviet Union, North America, Asia), but cases have also been reported in Uganda and Chile.
• Fish infected with Diphyllobothrium larvae may be transported to and consumed in any area of the world.
• Adequately freezing or cooking fish will kill the parasite.

Proglottids of Diphyllobothrium latum

Signs and symptoms

• Most infections are asymptomatic. However symptoms can include abdominal discomfort, diarrhea, vomiting, and weight loss.
• Vitamin B12 deficiency leading to pernicious anemia may occur. Complications include intestinal obstruction and gall bladder disease caused by migration of proglottids.

Diagnosis

• Diagnosis is made by identification of eggs or segments of the tapeworm in a stool sample with a microscope.
• Eggs are usually numerous, but more than one stool sample may be needed to find them.

Dibothriocephalus latus with ruler

Risk factors

• You got infected by eating raw or undercooked fish. Examples of fish include salmon, trout, perch, walleyed pike, and other species — usually freshwater fish.
• Some fish such as salmon live in both fresh and salt water and can harbor Diphyllobothrium larvae.
• Lightly salted, smoked, or pickled fish also may contain infectious organisms.
• Diphyllobothrium infection generally occurs in the Northern Hemisphere (Europe, newly independent states of the Former Soviet Union, North America, Asia), but has been reported in Uganda and Chile.
• Fish infected with Diphyllobothrium larvae may be transported to and consumed in any area of the world.

Diphyllobothrium egg

Prevention

• Do not eat raw or undercooked fish.
• The FDA recommends the following for fish preparation or storage to kill parasites.
• Cooking
• Cook fish adequately (to an internal temperature of at least 145° F [~63° C]).
• Freezing
• At -4°F (-20°C) or below for 7 days (total time), or
• At -31°F (-35°C) or below until solid, and storing at -31°F (-35°C) or below for 15 hours, or
• At -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours.

Causal Agents

• Several members of the cestode (tapeworm) family Diphyllobothriidae are known to infect humans.
• These pseudophyllidean cestodes have a scolex bearing bothria (grooves), instead of suckers as in the cyclophyllidean cestodes (the group including nearly all human-infecting species).
• All species associated with human diphyllobothriid infections have marine or aquatic life cycles and transmission occurs via ingestion of undercooked fish.

Diphyllobothrid Life Cycle

Name change

• Recent research incorporating morphologic and molecular data has led to the re-classification and re-naming of most of the human-infecting diphyllobothriids.
• Dibothriocephalus latus (=Diphyllobothrium latum), the “broad fish tapeworm”, is usually assumed to be the most common agent of human diphyllobothriasis.
• However, it is possible that many historical cases were falsely attributed to this species.
• Dibothriocephalus nihonkaiense (=Diphyllobothrium nihonkaiense), Dibothriocephalus dendriticus (=Diphyllobothrium dendriticum), Diphyllobothrium stemmacephalum (=Diphyllobothrium stemmacephalum; =Diphyllobothrium yonagoense), Diphyllobothrium balaenopterae (=Diplogonoporus grandis; =Diplogonoporus balaenoptera), and Adenocephalus pacificus (=Diphyllobothrium pacificum) are also known to infect humans.
• Sporadic case reports exist involving several other diphyllobothriid species, although some of the species identifications in these reports are of questionable validity.

Dlatum proglottid

Life Cycle

• Eggs are passed unembryonated in feces. Under appropriate conditions, the eggs mature (approximately 18 to 20 days) image and yield oncospheres which develop into a coracidia. After ingestion by a suitable crustacean (first intermediate host) the coracidia develop into procercoid larvae.
• Procercoid larvae are released from the crustacean upon predation by the second intermediate host (usually a small fish) and migrate into the deeper tissues where they develop into a plerocercoid larvae (spargana), which is the infectious stage for the definitive host.
• Because humans do not generally eat these small fish species raw, the second intermediate host probably does not represent an important source of human infection.
• However, these small second intermediate hosts can be eaten by larger predator species that then serve as paratenic hosts.
• In this case, the plerocercoid migrates to the musculature of the larger predator fish; humans (and other definitive host species) acquire the parasite via consumption of undercooked paratenic host fish.
• In the definitive host, the plerocercoid develops into adult tapeworms in the small intestine.
• Adult diphyllobothriids attach to the intestinal mucosa by means of two bilateral groves (bothria) of their scolex.
• The adults can reach more than 10 m in length, with more than 3,000 proglottids.
• Immature eggs are discharged from the proglottids (up to 1,000,000 eggs per day per worm) and are passed in the feces.
• Eggs appear in the feces 5 to 6 weeks after infection.

Treatment

• Praziquantel, adults, 5-10 mg/kg orally in a single-dose therapy; the dosage for children is the same.

(Note: praziquantel should be taken with liquids during a meal.)

Alternatives

• Adults, niclosamide 2 gm orally once; children, 50 mg/kg (max 2 gm) orally once.

(Note: niclosamide must be chewed thoroughly or crushed and swallowed with a small amount of water.)

Oral praziquantel is available for human use in the United States.

Niclosamide is NOT available for human use in the United States.

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