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Presentation of Quiz #41

A 56-year old woman presented to the emergency room complaining that she had a serious disease related to her "loss of intestines" while passing a stool several hours before. She had brought a large jar with her, which contained a long, white ribbon-like structure. The "ribbon" was about 3 ft long, 1/2 inch wide and was actively moving. On close examination, it appeared to be segmented. Other than this dramatic event, she had been well, had a good appetite, and had no documented illnesses during the past several years.

On examination, the patient revealed normal lungs, heart, and abdomen. Hematology and urinalysis findings were all within normal range. The "ribbon" was submitted to the microbiology laboratory for examination.

Laboratory results revealed the following image:

This image shows a portion (several inches) of the "ribbon" that was submitted to the laboratory for examination. Note that the "pieces" tend to be linked together and each "piece" appears to be wider than long. Based on this morphology, please respond to the questions found below.

What do you think this structure is? Why? What else would you like to see in order to confirm the identification? Why?

This case is adapted from a case reported by Dr. David N. Reifsnyder.

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Answer and Discussion of Quiz #41

The image presented in Diagnostic Quiz #41 is the following:

  1. This image contains a series of proglottids of the broad fish tapeworm (freshwater), Diphyllobothrium latum. Note that the proglottids are linked together and each individual proglottid is wider than it is long (unlike the proglottids of the Taenia species).

In order to confirm the infection, it would also be helpful to see/identify the typical tapeworm eggs.


D. latum belongs to the pseudophyllidean tapeworm group, which is characterized by having a scolex with two bothria (sucking organs) rather than the typical four suckers seen in the Taenia tapeworms. The distribution of this worm is worldwide, with various increased outbreaks reported from time to time. The infection is acquired by the ingestion of raw, poorly cooked, or pickled freshwater fish and has been associated with a condition similar to pernicious anemia.

Life Cycle:

Infection with the adult worm is acquired by the ingestion of raw, poorly cooked, or pickled freshwater fish (pike, perch, lawyer, salmon, trout, white fish, grayling, ruff, burbot, etc.) containing the encysted plerocercoid larvae. After ingestion, the worm matures, with egg production beginning in about the fifth or sixth week. The adult worm reaches a length of 10 m or more and may contain up to 3,000 proglottids.

The scolex of D. latum is elongate and spoon shaped and has two long sucking grooves, one on the dorsal surface and the other on the ventral surface. The mature and gravid proglottids are wider than long, with the main reproductive structures (mainly the uterus) located in the center of the gravid proglottid. This configuration of the uterine structure has been called a rosette. Identification to the species level is usually based on this typical morphology of the gravid proglottids. Both eggs and proglottids may be found in the stool. Often a partial chain of proglottids may be passed (a few inches to several feet). The eggs are broadly oval and operculated. After developing for 2 weeks in fresh water, the eggs hatch and the ciliated, coracidium larvae are ingested by the first intermediate host, the copepod. The copepods, containing the second larval stage (procercoid), are then ingested by fish, which may be ingested by larger fish. In this situation, the final fish intermediate host may contain many plerocercoid larvae, which initiate the infection with the adult worm when ingested by humans.

Clinical Disease:

Symptoms in the patient depend on a number of variables: the number of worms present, the amounts and types of by-products produced by the worm, the patient's reaction to such by-products, and the absorption of various metabolites by the worms. There may be occasional intestinal obstruction, diarrhea, abdominal pain, or anemia. If the worm is attached at the jejunal level, there may be a vitamin B12 deficiency which resembles pernicious anemia and which develops in a very small percentage of persons harboring the tapeworm. The clinical picture is seen most frequently in Finland, where individuals tend to have a genetic predisposition to pernicious anemia. In patients without this genetic predisposition, symptoms of a D. latum infection may be absent or minimal, with a slight leukocytosis with eosinophilia.


Diagnosis is usually based on the recovery and identification of the characteristic eggs or proglottids. If the egg operculum is difficult to see, the coverslip of the wet preparation can be tapped and the pressure may cause the operculum to pop open, thus making it more visible. The eggs are unembryonated at the time they are passed in the stool. Proglottids are often passed in chains (a few inches to several feet), and this is a clue to D. latum. The overall proglottid morphology with the rosette uterine structure also facilitates identification.

Epidemiology and Control:

Although D. latum infections have been recorded in other mammals, in areas where human infection has become rare, the natural transmission cycle from mammals other than humans does not seem to be sustained. It is quite possible to acquire the infection from the ingestion of infected raw freshwater fish that has been shipped under refrigeration to areas where the infection is not endemic. Preventive measures would include thorough cooking of all freshwater fish and freezing for 24 to 48 hours at ~18 C. This infection has been called the Jewish housewives' disease, since the individual preparing the food may sample the dish (e.g., gefilte fish) prior to cooking and acquire the infection. Other groups who tend to eat raw or insufficiently cooked fish include the Russians, Finns, and Scandinavians. Raw fish marinated in lime juice (ceviche) is also a source of infection (D. pacificum) in Latin America. Since the domestic dog can serve as a reservoir host, those that are infected should be periodically treated.

Diphyllobothrium latum Key Points--Laboratory Diagnosis

  1. Careful examination of the eggs should reveal the operculum. If it is difficult to see, it can sometimes be popped open by tapping on the coverslip of the wet preparation. The light should be somewhat reduced to allow the operculum to be seen more easily.
  2. Often the proglottids may be passed in chains (a few inches to a few feet). Also, the gravid proglottids will be much wider than long, with the uterine structure being seen in the middle of the proglottid (rosette).
  3. Handling of the specimens presents no danger in terms of cysticercosis; however, all fecal specimens should be considered potentially infectious (with other organisms).

Treatment: The use of both praziquantel and niclosamide has been recommended. After therapy, if the worm has not been spontaneously passed within 2 h, then a saline purgation can be used.

Three images of Diphyllobothrium latumfrom positive stool specimens (from left to right: egg seen in wet preparation from fecal concentration; Note the "bump" at the abopercular end and the fact that there are no opercular "shoulders" into which the operculum fits. The center image represents an additional egg where the operculum has popped open; if pressure is applied to the coverslip wet preparation, some of the egg opercula will pop. The right image is of several proglottids; note they are wider than long and all the reproductive structures are in the center of the proglottid (known as the "rosette" formation).


  1. Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.
  2. Garcia, L.S. 2009. Practical Guide to Diagnostic Parasitology, 2nd Ed., ASM Press, Washington, D.C.