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Chapter 14 : Tissue Cestodes: Larval Forms
This chapter discusses tissue cestodes in larval forms. Currently, four species are recognized within the genus Echinococcus: E. granulosus (which causes cystic disease), E. multilocularis (which causes alveolar disease), E. vogeli (which causes polycystic disease), and E. oligarthrus (which causes polycystic disease). The majority of hydatid cysts occur in the liver, causing symptoms that may include chronic abdominal discomfort, occasionally with a palpable or visible abdominal mass. Alveolar hydatid disease is the most lethal of helminthic diseases, with radical surgery still being the only curative therapy. This approach may also provide another procedure for the diagnosis of alveolar hydatid disease. The use of coproantigen testing by a sandwich enzyme-linked immunosorbent assay (ELISA) method to detect infection in foxes is more sensitive than routine egg detection assays and has been recommended for diagnosis in the definitive host of E. multilocularis. Coprodiagnosis by PCR is an excellent alternative to necropsy, since the sensitivity of necropsy is no higher than 76%. The PCR system is an alternative, sensitive method for the routine diagnosis of E. multilocularis in carnivores. Nine patients from Brazil were found to have polycystic hydatid disease, and the diagnosis was based on the shape and dimensions of the rostellar hooks. The larval forms (spargana) of Spirometra mansonoides and Diphyllobothrium spp. were first recognized in humans from tissues removed at autopsy. Although cases have been reported worldwide, sparganosis is most common in China, Japan, and Southeast Asia. This rare form of sparganosis can be diagnosed by histologic examination.
Life cycle of Echinococcus granulosus (cystic echinococcosis).
Adult worm of Echinococcus granulosus. (A) Diagram. (B) Whole mount (note that only three proglottids are present in the adult worm).
Echinococcus granulosus. (Top) Daughter cyst within the main cyst wall. (Middle) Hydatid sand (immature scolices). (Bottom) Individual hooklets. (Top image from A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Echinococcus granulosus hydatid cyst. (A) Diagram of unilocular cyst (limiting membrane). (B) Diagram of single immature worm. (C) Diagram of hooklets. (D) Diagram of laminated layers, daughter cysts, and scolices. (Illustration by Sharon Belkin.) GL, germinal layer; LL, laminated layer; FL, fibrous layer.
Hydatid cysts in liver. This patient had three cysts (marked by arrows) in the right lobe. Two were completely calcified, and the large one in the background was partially calcified. (From V. Zaman, Atlas of Medical Parasitology, Lea & Febiger, Philadelphia, Pa., 1979.)
Hydatid cyst in the lung. This patient had a single large cyst in the left lung. There was collapse and consolidation in part of the left lung as a result of pressure on the bronchus. Partial pneumonectomy was required to remove the cyst. (From V. Zaman, Atlas of Medical Parasitology, Lea & Febiger, Philadelphia, Pa., 1979.)
Echinococcus granulosus calcified liver cyst. The cyst is visible at the upper edge of the right pelvis; the dense pearlike structure is the gallbladder. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Life cycle of Echinococcus multilocularis (alveolar hydatid disease).
Echinococcus multilocularis. (A) Entire cyst. (B) Multicystic nature of the parasite in an experimental infection in a muskrat. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of R. L. Rausche.) (C) Diagram of a histologic section (the left side represents the normal animal intermediate host in which scolices are found; the right side demonstrates the cyst structure within the human accidental intermediate host in which the scolices may not develop). (D) Histologic section. (Illustration by Sharon Belkin.)
Polycystic hydatid disease.
Life cycle of Taenia (Multiceps) spp.
Representative cysts. (A) Cysticercus; (B) coenurus; (C) hydatid; (D) multilocular hydatid. (Illustration by Sharon Belkin.)
Coenurosis. (Upper) Diagram of cyst. (Illustration by Sharon Belkin.) (Lower left) Actual cyst. (Armed Forces Institute of Pathology photograph.) (Lower right) Actual cyst. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of J. Harper III and L. C. Marcus.)
Coenurosis: cross section of cyst. (Armed Forces Institute of Pathology photograph.)
Life cycle of Spirometra mansonoides and Diphyllobothrium spp. (sparganosis).
Echinococcus granulosus strains a
Examples of hydatid disease, complications, and/or outcomes
Antibody detection tests for human cystic and alveolar echinococcosis a
Procedures for the diagnosis of echinococcosis
Additional information on therapy for hydatid disease
Examples of epidemiology of cystic hydatid disease (E. granulosus)
Control measures for cystic hydatid disease
Infection phases: alveolar echinococcosis
Additional information on therapy for alveolar hydatid disease
Variables in the epidemiology of alveolar echinococcosis a