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A 48-year-old white female presented with nausea, vomiting, and watery diarrhea of 1-day duration. She reported having eaten out the previous night, but otherwise had no significant medical history. She was febrile (101.2°F), hypotensive (80/50 mm Hg), and hypokalemic (K = 2.1 mEq/L) with a normal electrocardiogram. Preliminary diagnosis was dehydration and hypokalemia secondary to acute gastritis, and she was started on fluid and potassium supplementation. Overnight, her symptoms improved and the hypokalemia resolved. She reported having a loose bowel movement and passing a piece of “rubbery fettuccine.” Stool examination revealed segments of a worm, subsequently identified as proglottides of the fish tapeworm, Diphyllobothrium latum. On questioning, the patient recalled eating sashimi at a sushi bar 4 months earlier. Praziquantel was given, and she was discharged. Subsequent stool examinations 1 month later showed no sign of worm infestation.
Human infection with D. latum is typically acquired by eating uncooked or undercooked freshwater salmonid fish, which harbors the parasite’s larvae. Once ingested, it takes 3 to 6 weeks for the larvae to mature into adult tapeworms. It can survive up to 30 years, reaching sizes up to 25 m long. Although usually asymptomatic, reported symptoms include intermittent abdominal cramping and distension, flatulence, and diarrhea. Approximately 40% of infested individuals have low vitamin B12 levels, but megaloblastic anemia is uncommon (<2%). Anemia, if present, is caused by parasite-mediated dissociation of the vitamin B12-intrinsic factor complex and competitive vitamin uptake by the worm. D. latum absorbs between 80% and 100% of an oral dose of radioactive B12.
Diphyllobothrium-induced anemia cannot be differentiated from other types of megaloblastic anemia. Adult worms may cause eosinophilia and immunoglobulin-E elevation. Detection of characteristic operculated eggs or intact proglottides (Figure 1) in a stool sample is confirmatory.
Anemia usually resolves once the worm has been eradicated.
Because the worm requires intermediate hosts, direct human-to-human transmission does not occur; thus no isolation measures are required. Cooking fresh fish to temperatures of at least 56°C for 5 minutes or freezing to −18°C for 24 hours can prevent infestation.
Historically, Diphyllobothriasis has been endemic in regions where consumption of uncooked and pickled fish is popular. In the United States no recent cases have been reported, and it is thought that the incidence of the disease is on the decline.
Is this a real phenomenon or an artifact of monitoring because this is not a reportable disease? Many carriers go undetected because infected individuals are usually asymptomatic, and repeated stool examinations may be needed to isolate the eggs. A high index of suspicion and repeat stool examinations are thus needed to identify carriers in those who present only with anemia if there is a history of eating raw fish. Newer immunologic and molecular tools of diagnosis and differentiation may be developed for specific diagnosis. Because of the asymptomatic nature of the infection and the increasing popularity of ethnic raw salmonid delicacies like sushi, sashimi, and ceviche in the United States, the incidence of the disease may not be on the decline; rather, we may be experiencing a silent epidemic of diphyllobothriasis.