Full text loading...
Chapter 16 : Liver and Lung Trematodes
Paragonimus spp., also known as lung flukes, cause paragonimiasis in humans. The infections caused by the liver and lung trematodes are food borne and have considerable economic and public health impact. Of great public health concern is cholangiocarcinoma associated with Clonorchis and Opisthorchis infections, severe liver disease associated with Fasciola infections, and the misdiagnosis of tuberculosis in those infected with Paragonimus spp. In the Far East, forms of chronic inflammation associated with cholangiocarcinoma include infestation with either of the liver flukes, Clonorchis sinensis or Opisthorchis viverrini. Cholangiography, ultrasonography, and liver scans may reveal lesions consistent with liver fluke infection. Like infections with other liver flukes, the degree of clinical involvement depends on the extent and duration of the infection. Abscess or tumorlike reactions have also been reported to occur in subcutaneous tissues or in the liver. Symptoms of paragonimiasis depend largely on the worm burden of the host and are usually insidious in onset and mild in patients with chronic infections. The patient may experience increasing dyspnea with chronic bronchitis and be misdiagnosed as having tuberculosis or bronchial asthma. The most serious consequences of paragonimiasis are the cerebral complications, which are commonly found in younger age groups. Unlike adult flukes in other extrapulmonary sites, worms found in the brain usually contain eggs. Pulmonary paragonimiasis is rarely fatal; however, cerebral disease is characterized by chronic morbidity and symptoms including epilepsy, dementia, and other neurologic sequelae.
Life cycle of the liver and lung trematodes.
Eggs of Clonorchis sinensis. Note the range of sizes and shapes.
Clonorchis sinensis adult (10 to 25 mm long by 3 to 5 mm wide). (Armed Forces Institute of Pathology photograph.)
Adult liver and lung trematodes. (A) Fasciola hepatica; (B) Paragonimus westermani; (C) Clonorchis sinensis; (D) Opisthorchis viverrini and O. felineus.
Clonorchis sinensis adult in a biliary duct (cross section). (Panel A, Armed Forces Institute of Pathology photograph; panel B, from A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Opisthorchis viverrini adult trematode.
Opisthorchis felineus adult trematode.
Fasciola hepatica adult worm (upper left), egg (upper right), and living worm (lower). The operculum can be difficult to see; this egg resembles that of F. buski (intestinal trematodes) and F. gigantica (liver trematodes), although the egg of F. gigantica is larger. The F. hepatica adult worm is 20 to 30 mm long by 8 to 13 mm wide.
Fasciola hepatica adult worm in a bile duct; note the U-shaped worm within the bile duct with surrounding tissues.
Fasciola hepatica adult worm in the liver; note the U-shaped worm with surrounding hepatic tissue, with a cellular response seen around the worm.
Fasciola gigantica adult worm (left) and egg (right). The operculum can be difficult to see; this egg resembles that of F. buski (intestinal trematodes) and F. hepatica (liver trematodes), although the egg of F. gigantica is larger (160 to 190 μm by 70 to 90 μm). The F. gigantica adult worm is 25 to 75 mm long by 12 mm wide. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Paragonimus westermani adult worm (left) and egg (right). The opercular shoulders are clearly visible at the top of the egg, as is the thickened abopercular end.
Photographs (top) and drawings (bottom) of Diphyllobothrium latum egg (A) and Paragonimus westermani egg (B). (Illustration by Nobuko Kitamura.)
Crab second intermediate host for Paragonimus spp.
Paragonimus westermani egg in the lung (cross section). (Armed Forces Institute of Pathology photograph.)
(Upper) Paragonimus westermani egg in brain granuloma (cross section). (Armed Forces Institute of Pathology photograph.) (Lower) P. westermani eggs in brain tissue. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Characteristics of liver and lung trematodes
Possible means of acquiring infection with Paragonimus spp. a