eMedicine Specialties > Infectious Diseases > Parasitic Infections
Trematode Infection: Multimedia
Updated: Nov 13, 2009
Multimedia
 | Media file 1: Trematode infection. Adult worms in humans reside in the veins in various locations: Schistosoma mansoni in the superior mesenteric veins, Schistosoma japonicum in the inferior mesenteric veins, and Schistosoma haematobium in the vesical veins (these locations are not absolute). The females (size 7-20 mm; males slightly smaller) deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S mansoni and S japonicum) and of the bladder and ureters (S haematobium), and they are eliminated with feces or urine, respectively. Under optimal conditions, the eggs hatch and release miracidia, which swim and penetrate specific snail intermediate hosts. The stages in the snail include 2 generations of sporocysts and the production of cercariae. Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host, and migrate through several tissues and stages to their residence in the veins. Human contact with water is thus necessary for infection by schistosomes. Various animals serve as reservoirs for S japonicum and Schistosoma mekongi. Image courtesy of the US Centers for Disease Control and Prevention. |
 | Media file 2: Trematode infection. Clonorchis sinensis egg. These are small operculated eggs. Size is 27-35 μm X 11-20 μm. The operculum, at the smaller end of the egg, is convex and rests on a visible "shoulder." At the opposite (larger, abopercular) end, a small knob or hooklike protrusion is often visible (as here). The miracidium is visible inside the egg. Image courtesy of the US Centers for Disease Control and Prevention. |
 | Media file 3: Trematode infection. Fasciola hepatica eggs. Wet mounts with iodine. The eggs are ellipsoidal. They have a small, barely distinct operculum (upper end of the eggs in panel A). The operculum can be opened (egg in panel B), for example, when slight pressure is applied to the coverslip. The eggs have a thin shell that is slightly thicker at the abopercular end. They are passed unembryonated. Size range is 120-150 μm X 63-90 μm. Image courtesy of the US Centers for Disease Control and Prevention. |
 | Media file 4: Trematode infection. Adult fluke of Fasciolopsis buski. Adult flukes size range is 20-75 mm by 8-20 mm. Image courtesy of the US Centers for Disease Control and Prevention. |
 | Media file 5: Trematode infection. Eggs are excreted unembryonated in the sputum, or, alternately, they are swallowed and passed with stool (1). In the external environment, the eggs become embryonated (2), and miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues (3). Miracidia go through several developmental stages inside the snail (4): sporocysts (4a), rediae (4b), with the latter giving rise to many cercariae (4c), which emerge from the snail. The cercariae invade the second intermediate host, a crustacean such as a crab or crayfish, in which they encyst and become metacercariae. This is the infective stage for the mammalian host (5). Human infection with Paragonimus westermani occurs by eating inadequately cooked or pickled crab or crayfish that harbor metacercariae of the parasite (6). The metacercariae excyst in the duodenum (7), penetrate through the intestinal wall into the peritoneal cavity, and then through the abdominal wall and diaphragm into the lungs, where they become encapsulated and develop into adults (8) (7.5-12 mm X 4-6 mm). The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively. However, when this occurs, completion of the life cycle is not achieved because the eggs laid cannot exit these sites. Time from infection to oviposition is 65-90 days. Infections may persist for 20 years in humans. Animals such as pigs, dogs, and a variety of feline species can also harbor P westermani. Image courtesy of the US Centers for Disease Control and Prevention. |
 | Media file 6: Trematode infection. Paragonimus westermani egg. The average egg size is 85 μm by 53 μm (range, 68-118 μm X 39-67 μm). They are yellow-brown, ovoidal or elongate, have a thick shell, and are often asymmetrical with one end slightly flattened. At the large end, the operculum is clearly visible. The opposite (abopercular) end is thickened. The eggs of P westermani are excreted unembryonated. Image courtesy of the US Centers for Disease Control and Prevention. |
More on Trematode Infection |
| Overview: Trematode Infection |
| Differential Diagnoses & Workup: Trematode Infection |
| Treatment & Medication: Trematode Infection |
| Follow-up: Trematode Infection |
 Multimedia: Trematode Infection |
| References |
| « Previous Page |
References
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Anuracpreeda P, Wanichanon C, Chawengkirtikul R, Chaithirayanon K, Sobhon P. Fasciola gigantica: Immunodiagnosis of fasciolosis by detection of circulating 28.5kDa tegumental antigen. Exp Parasitol. Dec 2009;123(4):334-40. [Medline].
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Further Reading
Keywords
trematode infection, trematodiasis, parasites, parasitemia, flukes, blood fluke, lung fluke, liver fluke, intestinal fluke, species, schistosomes, Oriental lung fluke, giant intestinal fluke, schistosomiasis, pulmonary paragonimiasis, paragonimiasis, swimmer's itch, swimmer itch, cercarial dermatitis, Katayama syndrome, fascioliasis, clonorchiasis, schistosomal infection, fasciolopsiasis, heterophyiasis, metagonimiasis, pyogenic cholangitis, hemiplegia, cephalgia, paresis, cholangiocarcinoma, bilharzia, fasciolosis
