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Presentation of Quiz #43

A 34-year-old man from Mexico went to the clinic because he found some white, rectangular objects in his stool specimen. These objects appeared to be "moving" very slowly. He had always been healthy, and had come to the United States 2 years earlier. He denied any gastrointestinal or other symptoms. He had lived in a rural area of Mexico, and reported no unusual dietary habits or significant contact with animals. During the last few days, he complained of anorexia, some nausea, and abdominal cramps; however, he had no diarrhea.

Laboratory findings were normal; however, the routine O&P examination revealed the following:

Examples of helminth eggs; photographed using the high dry (40X) objective

The structure below was brought in by the patient and measured approximately 1" by 3/8" and appeared to be a very pale tan color (almost white) - this image was obtained after staining.

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Answer and Discussion of Quiz #43

The images presented in Diagnostic Quiz #43 are the following:

  1. The three helminth eggs are those of Taenia spp. From the egg morphology, it is impossible to identify the cestode to the species level, either T. saginata (beef tapeworm) or T. solium (pork tapeworm).
  2. This structure recovered from the patient's stool specimen is a T. saginata proglottid (after injection of the uterine structure with India ink).

Comment:

This is a case of a woman who was infected with the beef tapeworm, Taenia saginata. The life cycle is very similar to that of T. solium (pork tapeworm). Infection with the adult worm is initiated by the ingestion of raw or poorly cooked beef containing encysted T. saginata larvae (cysticerci). As with T. solium, the larva is digested out of the meat in the stomach, and the tapeworm evaginates in the upper small intestine and attaches to the intestinal mucosa, where the adult worm matures within 5 to 12 weeks. The adult worm can reach a length of 25 m but often measures only about half this length. Although a single worm is usually found, there can be multiple worms present (personal observation).

The scolex is ``unarmed'' and has four suckers with no hooks. The proglottids usually number 1,000 to 2,000, with the mature proglottids being wider than long and the gravid proglottids being narrower and longer. Identification to the species level is usually based on the number of main lateral uterine branches, which are counted on one side of the gravid proglottid. There are between 15 and 20 branches, with an average of 18

Gravid proglottids often crawl from the anus during the day, when the host is most active. These proglottids may crawl under the stool when a specimen is submitted unpreserved in the stool collection carton. The eggs cannot be distinguished from those of T. solium. They are round to slightly oval, measure 31 to 43 µ, have a thick, striated shell, and contain the six-hooked embryo (oncosphere). The eggs can remain viable in the soil for days to weeks. Upon ingestion by cattle, the oncospheres hatch in the duodenum, penetrate the intestinal wall, and are carried via the lymphatics or bloodstream, where they are filtered out in the striated muscle. They then develop into the bladder worm or cysticercus within approximately 70 days. The mature cysticercus measures 7.5 to 10 mm wide by 4 to 6 mm long and contains the immature scolex, which has no hooks (unarmed). Other animals found to harbor cysticerci include buffalo, giraffe, llama, and possibly reindeer). Actual cases of human cysticercosis with T. saginata are rare in the literature, and there is speculation that some reported cases have been inaccurately diagnosed.

There are usually few symptoms associated with the presence of the adult worm in the intestine. Although rare symptoms (obstruction, diarrhea, hunger pains, weight loss, and appendicitis) have been reported, the most common complaint is the discomfort and embarrassment caused by the proglottids crawling from the anus. This occurrence may be the first clue that the patient has a tapeworm infection. Occasionally, the proglottids may also be seen on the surface of the stool after it is passed

Taenia saginata Key Points -- Laboratory Diagnosis

  1. Preliminary examination of the gravid proglottid may not allow identification without clearing or injection of the uterine branches with India ink. Note Since there is always the possible danger that the proglottid is T. solium, with the inherent problem of egg ingestion and cysticercosis, all specimens should be handled with extreme caution.
  2. The eggs look identical to those of T. solium, so identification to the species level cannot be performed with eggs alone.
  3. Although gravid proglottids of T. saginata are often somewhat larger than those of T. solium, this difference may be very minimal or impossible to detect.
  4. Any patient with Taenia eggs recovered in the stool should be cautioned to use good hygiene. These patients should be treated as soon as possible to avoid the potential danger of accidental infection with the eggs, which may lead to cysticercosis (T. solium).

For therapy, the use of praziquantel or niclosamide has been recommended. The same general approach as used for T. solium is used to eradicate the adult worm. Therapy is usually very effective; however, if the proglottids begin to reappear in the stool or crawl from the anus, then retreatment will be necessary.

T. saginata gravid proglottid; Congo red staining after India ink injection of uterine branches

T. saginata scolex; note four suckers and no hooklets

References:

  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.