eMedicine Specialties > Infectious Diseases > Parasitic Infections

Diphyllobothriasis

Author: Derek Ryan Linklater, MD, Assistant Professor of Military and Emergency Medicine, F Edward Hebert School Of Medicine; Assistant Clinical Professor of Emergency Medicine, Texas A&M Health Science Center College of Medicine; Clinical Instructor of Pediatrics, Baylor College of Medicine
Coauthor(s): Coburn H Allen, MD, Assistant Professor, Department of Pediatrics, Section of Emergency Medicine and Section of Infectious Diseases, Baylor College of Medicine; Consulting Staff, Texas Children's Hospital
Contributor Information and Disclosures

Updated: Sep 26, 2008

Introduction

Background

Diphyllobothriasis is defined as infection with the cestode Diphyllobothrium latum or other Diphyllobothrium species. Cestodes, more commonly called tapeworms, are symmetric flatworms that parasitize the intestinal tract of vertebrates. Tapeworms consist of a head (scolex), a neck, and a germinal region that consists of a string of separate individual segments that have a full set of progressively maturing reproductive organs. The scolex attaches to the host's intestinal mucosa, and tapeworms grow when segments bud from the scolex. The segments enlarge by developing large numbers of eggs that are subsequently shed in the stool.

Cestodes are hermaphroditic and capable of self-fertilization, but Diphyllobothrium eggs must be passed into an aquatic environment to complete their development and become infective. Cestodes do not have a digestive tract at any stage of their development; consequently, they exchange nutrients and waste through their body covering (tegument). The tegument is covered by minute projections called microtriches, which lie in proximity to the host's intestinal villi and greatly increase the absorptive area of the flatworm.

Pathophysiology

Adult Diphyllobothrium worms range from 1-12 m in length, have proglottids that are wider than their length, and discharge ovoid eggs that measure 60 µm X 40 µm. The life cycle of Diphyllobothrium species begins with an infected host discharging eggs into a freshwater environment that contains susceptible crustaceans and fish. After the eggs hatch, the embryonic flatworms are ingested by water fleas; in these crustaceans, the first larval stage develops. When a fish devours the infected crustacean, a second larval stage develops, and this larva is infective to the definitive hosts. The juvenile worm develops to maturity in the small intestine of the definitive host and, within 3-5 weeks, begins to produce eggs. Adult Diphyllobothrium worms have a lifespan that may exceed 10 years.

Frequency

United States

In North America, D latum infections have been reported in fish from the Great Lakes; however, no infections have recently been reported, and the worm may have ceased to reside in this area. Eskimos have also reported diphyllobothriasis, and 6 Diphyllobothrium species are known to reside in Alaskan lakes and rivers. Diphyllobothriasis is not a species-specific infection, and widespread reports have described infection in North American fish-eating birds and mammals. The incidence of diphyllobothriasis in the United States has been declining, but the growing popularity of Japanese sushi and sashimi has the potential to increase the frequency of infection. Pike, perch, and salmon (80% in a recent case series) are among the fish most commonly infected.

International

D latum commonly infects persons residing in Europe, Africa, and the Far East. Dietary preferences, night soil (human excrement) fertilization practices, and poor sanitation seem to be responsible for the increased incidence of diphyllobothriasis in these countries.

Mortality/Morbidity

D latum is not invasive, and mortality due to diphyllobothriasis is rare. Individuals with diphyllobothriasis are commonly asymptomatic. When present, diphyllobothriasis symptoms are usually related to vitamin deficiencies and anemia.

Race

Diphyllobothriasis has no known racial predilection, except as would be expected based on geographic and cultural factors.

Sex

Diphyllobothriasis has no reported sexual predilection.

Age

Diphyllobothriasis has no reported age predilection.

Clinical

History

Most persons with diphyllobothriasis are asymptomatic.

Among symptomatic persons, the following symptoms are most common:¹

• Abdominal pain
• Indigestion/dyspepsia
• Passage of proglottids

Other, less common, symptoms of diphyllobothriasis include the following:

• Fatigue
• Diarrhea
• Dizziness
• Weakness (rare)
• Numbness of extremities
• Sensation of hunger
• Pruritus ani

Physical

D latum has an unusual affinity for vitamin B-12, and symptoms of diphyllobothriasis clinically resemble those of megaloblastic anemia. Most patients with diphyllobothriasis have no signs of illness because significant anemia affects less than 2% of persons infected with D latum. The following physical findings associated with diphyllobothriasis are rare and are most likely related to underlying nutritional anemia:

• Pallor
• Glossitis
• Dyspnea
• Tachycardia
• Weakness
• Hypesthesia
• Paresthesias
• Disturbances of movement and coordination

Causes

Diphyllobothriasis is caused by ingestion of raw or undercooked infected fish and subsequent intestinal infection.

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