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Category: Clinical Microbiology
Intestinal Cestodes, Page 1 of 2
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Cestodes have complex life cycles that usually involve both the intermediate and definitive hosts. In some infections, humans serve as only the definitive hosts, with the adult worm in the intestine (Diphyllobothrium latum, Taenia saginata, Hymenolepis diminuta, and Dipylidium caninum). In other cases, humans can serve as both the definitive and intermediate hosts (Taeniasis solium and Hymenolepsis nana). About 40% of patients infected with D. latum have reduced vitamin B12 levels, but fewer than 2% develop anemia. The use of both praziquantel and niclosamide has been recommended. A single dose of praziquantel (5 to 10 mg/kg of body weight) both adults and children eliminates the infection in 90% of patients. Cysticercosis infections with T. solium larvae are relatively common in certain parts of the world. The presence of cysticerci in the brain represents the most frequent parasitic infection of the human nervous system and the most common cause of adult-onset epilepsy throughout the world. For a number of reasons, T. solium is a candidate for control: (i) neurocysticercosis has a tremendous impact on human health; (ii) since T. solium is the only source of cysticercosis for both humans and pigs, it may be epidemiologically controllable; (iii) effective and practical therapeutic intervention is available; (iv) international commitment to the use of control measures is present; and (v) the cost is acceptable. The chapter talks about T. saginata, T. saginata asiatica, Hymenolepis nana, Hymenolepis diminuta, and Dipylidium caninum.
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Taenia solium, T. saginata, and Diphyllobothrium latum.
Life cycle of Diphyllobothrium latum.
Scolex of Diphyllobothrium latum.
Gravid proglottids of Diphyllobothrium latum. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Slides from J. F. Mueller.)
Diphyllobothrium latum eggs. Note the small knob at the abopercular end (end opposite the operculum); also note that the operculum does not fit into “shoulders” like the Paragonimus eggs but presents a smooth outline on the egg shell.
Copepod. (Illustration by Sharon Belkin.)
Diphyllobothrium latum, encysted pleurocercoids in cherry salmon fillet. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of T. Oshima, Yokohama City University.)
Life cycle of Taenia solium.
(A) Cysticerci in muscle (pork). (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.) (B) Cysticerci in muscle (dog). (Courtesy of W. Jann Brown and Marietta Voge, University of California, Los Angeles.)
Scolex of Taenia solium.
Gravid proglottid of Taenia solium.
Taenia eggs. Note the striated shell and the presence of the six-hooked oncosphere within the thick egg shell. The hooks may not be visible in every egg, particularly in specimens that have been stored for long periods in preservatives; however, in clinical specimens submitted to the laboratory in fixatives for timely examination, the hooklets are generally visible within the egg shell. Without special staining, the eggs of Taenia spp. cannot be identified to the species level (T. solium, T. saginata, T. asiatica).
(A) Cysticercus with head invaginated into the bladder. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.) (B) Scanning electron micrograph of scolex from cysticercus. (Photograph courtesy of U.S. Department of Agriculture).
Gross specimen of brain containing many cysticerci. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Cysticercus in the eye. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of R. Delgado y Garnica, Hospital Infantil de Tacubaya, Arq. Carlos Laxo y Gaviota, Mexico D.F.)
Racemose form of Taenia solium cysticercus, left temporal lobe (filmy, white material). (Courtesy of W. Jann Brown and Marietta Voge, University of California, Los Angeles.)
Taenia solium. Section of proliferating bladder wall of racemose cysticercus, demonstrating multiple layers. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Calcified cysticerci in tissue. (Armed Forces Institute of Pathology photograph.)
Neurocysticercosis. Scanning images of cysticerci in brain. (Upper, adapted from the Public Health Image Library, Centers for Disease Control and Prevention; lower, from A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Life cycle of Taenia saginata. The same life cycle is applicable to T. asiatica (except that the eggs are contained primarily in the liver of the pig).
Scolex of Taenia saginata.
Gravid proglottid of Taenia saginata.
Taenia saginata asiatica (Taenia asiatica). (Left) Scolex (unarmed, no hooks) from cysticercus; (right) scolex from adult worm. (Photographs courtesy of Ping-Chin Fan, with permission.)
Taenia saginata asiatica (Taenia asiatica). (Upper) Gravid proglottid. (Lower) Gravid proglottid (note the large number of uterine branches and the similarity of this proglottid to the one of Taenia saginata in Figure 13.22 ). (Photographs courtesy of Ping-Chin Fan, with permission.)
Taenia saginata asiatica (Taenia asiatica). Cross section of cysticercus. (Photograph courtesy of Ping-Chin Fan, with permission.)
Life cycle of Hymenolepis nana.
Hymenolepis nana. (Upper) Diagram of both a cysticercoid and adult worm in the small intestine. (Illustration by Sharon Belkin.) (Lower) Cysticercoids of H. nana in the villi of the small intestine. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
(Left) Egg of Hymenolepis nana (note the thin egg shell, the six-hooked oncosphere, and the polar filaments that lie between the oncosphere and egg shell). (Right) Egg of Hymenolepis diminuta (note the thin egg shell, the six-hooked oncosphere, and the lack of polar filaments.)
Life cycle of Hymenolepis diminuta.
Life cycle of Dipylidium caninum.
Proglottids of Dipylidium caninum. (Upper) Fresh proglottid that may resemble a cucumber seed (note the shape and light color); when the proglottids dry, they may resemble rice grains. (Lower) Stained proglottid. (Photographs from the Centers for Disease Control and Prevention Program: Laboratory Identification of Parasites of Public Health Concern.)
Dipylidium caninum egg packets. (Upper) Diagram showing the packet of Taenia-like eggs. (Lower) Egg packet in wet mount preparation.
Cestode parasites (intestinal)
Classification of neurocysticercosis a