Approach Considerations
Most patients with diphyllobothriasis, unless they have severe symptoms, can be safely treated on an outpatient basis. Inpatient care is not generally required but may have to be considered in advanced, resistant, or complicated cases.
Diphyllobothriasis is treated by pharmacologic means; surgical treatment is not required unless otherwise indicated (eg, in a patient presenting with intestinal obstruction). Even in the face of decreased vitamin B12 levels, less than 2% of patients with diphyllobothriasis develop anemia. Vitamin supplementation may be required in severe cases. As a rule, no activity limitations or restrictions are necessary.
Pharmacologic Therapy
Treatment of diphyllobothriasis is pharmacologic. Because the parasite’s biochemical pathways are different from those of the human host, drug toxicity is directed toward the parasite, the egg, or the larvae.
Praziquantel is the drug of choice for Diphyllobothrium infections. [43] The exact mechanism of action in Diphyllobothrial infections is unclear; however, it has been proposed to lead to a rapid influx of calcium ions into schistosomes, with subsequent muscle contraction and paralysis. [44] Praziquantel is effective against D latum as a single dose of 25 mg/kg . A lower dose of 10 mg/kg has been reported to be effective against D pacificum.
Similarly, whereas a lower praziquantel dose of 5 to 10 mg/kg has been reported to be effective against D nihonkaiense, a single dose of 25 mg/kg is the typical dose administered. Side effects are typically minor and include headache, malaise, dizziness, and, rarely, urticaria. An alternative drug is niclosamide, which has limited availability in many countries and has been proposed to act by uncoupling oxidative phosphorylation. [43, 45] It is effective as a single oral dose of 2 g in adults and side effects rare. [1]
The neurologic and hematologic manifestations of vitamin B12 deficiency respond well to supplementation. In the case of vitamin B12 deficiency secondary to diphyllobothriasis, the signs and symptoms may resolve with antiparasitic therapy alone.
Note: Gastrografin, an iodine-based contrast agent combining diatrizoate and meglumine, used for diagnostic imaging of the intestine, is also a strong laxative and cathartic. Prior to the discovery of praziquantel, it was found to be effective in the rapid expulsion of the entire worm intact, including the scolex. Its use is limited because it requires delivery through a duodenal tube to maintain high concentration in the vicinity of the worm and fluoroscopy is needed. [1, 46]
Consultations
Resistant or advanced cases of diphyllobothriasis may require consultation with a gastroenterologist and an infectious disease specialist. Consultation with a hematologist may be considered, depending on the severity of anemia. In the case of suspected obstruction, consultation with a surgeon is indicated.
Long-Term Monitoring
The patient’s stool should be reexamined 1 to 2 months after therapy to test for cure. If the first course of treatment fails, a second identical course of therapy may be administered. [47, 48]
Complications
Rarely, infection with this parasite can lead to intestinal obstruction, cholangitis, subacute appendicitis and cholecystitis. [1, 5] Although more frequently reported in the past, infestation with Diphyllobothrium, particularly D latum can lead to complications associated with severe B12 deficiency, including megaloblastic anemia, peripheral neuropathy, and optic neuropathy. [1, 49]
Prevention
Diphyllobothrium infection can be prevented on a population level by appropriate sewage treatment, thus preventing human feces containing the eggs from entering water bodies and subsequent hosts of the parasite life cycle. [50] Furthermore, parasitic screening of fish prior to exportation and ensuring adequate freezing of fish during exportation are other key processes required to prevent spread of this disease. [18, 28] Adequate labeling of fish products attesting to the safety of preparation procedures is also a measure that would protect consumers from purchasing potentially contaminated fish. [50]
On an individual level, the US Centers for Disease Control and Prevention (CDC) recommends cooking fish to an internal temperature of 63°C (145°F) or higher, freezing fish to -4°F (-20°C) for 7 days or -31°F (-35°C) or less until solid, and storing at either -31°F (-65°C) or below for 15 hours or -4°F (-20°C) for 24 hours. [29] These precautions kill the plerocercoid larvae. The fish must never be sampled before it is properly prepared.
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Life cycle of diphyllobothrium.
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Egg of Diphyllobothrium latum with arrow pointing to operculum.
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Proglottids of Diphyllobothrium latum.
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Diphyllobothrium life cycle. This illustration depicts the life cycle of different species of Diphyllobothrium parasitic cestodes, the causal agents of the disease diphyllobothriasis. Courtesy of the Centers for Disease Control and Prevention (CDC) (https://www.cdc.gov/dpdx/diphyllobothriasis/).
Tables
Species |
Geography |
Fish |
Definitive Host |
Human Prevalence |
D latum |
Finland, Baltic States, Danube Delta, Karelia, Manitoba, Great Lakes |
Perch, pike, burbot |
Humans, dogs, wolves |
Millions |
D nihonkaiense |
North Pacific Coast, Japan, Korea, East Russia |
Salmon (cherry, chum, pink, sockeye) |
Brown and black bears, wolves, dogs, foxes, mink |
Thousands (March-June peak) |
D dendriticum |
Lake Baikal region, Subarctic North America, Russia, Rocky Mountains, Patagonia |
Whitefish, salmonids |
Gulls, bears, otter |
Thousands (600/year mostly) |
A pacificus |
Peru, Chile, Ecuador, Sakhalin Island |
Marine fish (bonito, mackerel, lorna drum, croaker) |
Sea lions, seals |
Thousands |
D balanopterae |
Japan, Spain, Norway, Korea |
Anchovy, sardines, skipjack tuna |
Whales |
Hundreds (June-July peak) |
