Diagnostic Considerations
Differential diagnoses of trematode eggs in feces include other trematodes, such as liver flukes or lung flukes (see below [40] and see Table 1).
Intestinal flukes
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Frequently asymptomatic
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Mild infection - Mild diarrhea, abdominal pain
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Severe infection - Malabsorption, intestinal obstruction, eosinophilia may be present
Liver flukes (opisthorchiasis, clonorchiasis)
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Frequently asymptomatic
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Acute infection - Serum sickness–like illness (similar to Katayama fever with high fever, eosinophilia, tender hepatomegaly, rash)
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Advanced stage - May be complicated by recurrent cholangitis, jaundice, associated with cholangiocarcinoma
Liver flukes (fascioliasis)
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Acute infection - High fever, right-upper-quadrant pain, hepatomegaly, eosinophilia, urticaria
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Chronic stage - Frequently asymptomatic, biliary obstructive symptoms, eosinophilia
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Ectopic infection - Visceral larva migrans–like, aberrant sites (eg, lungs, heart, brain, skin)
Lung flukes (paragonimiasis)
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Acute infection - Diarrhea and pain, eosinophilia, fever, cough, dyspnea, chest pain
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Pulmonary stage (after approximately 6 mo) - Chronic bronchitis symptoms progressing to pleurisy, hemoptysis, eosinophilia, pulmonary infiltrates with cysts, with or without thin-walled cavities and pleural effusions
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Cerebrospinal infection - Brain or spinal cord invasion with 1-10 cysts, meningoencephalitis or paraplegia in symptomatic infections (acute infections)
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Abdominal infection - Invasion into liver, spleen, or peritoneum
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Migratory subcutaneous infection - Firm, slightly mobile, tender cysts similar to trematode larva migrans
Differential Diagnoses
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Life cycle of Fasciolopsis buski. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
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The life cycle of Fasciolopsis. Immature eggs are discharged into the intestine and stool and become embryonated in water. The eggs then release miracidia, which invade a suitable snail intermediate host, in which the parasites undergo several developmental stages (sporocysts, rediae, cercariae). The cercariae are released from the snail and encyst as metacercariae on aquatic plants, which are eaten by mammalian hosts (humans and pigs), who become infected. After ingestion, the metacercariae excyst in the duodenum and attach to the intestinal wall, where they develop into adult flukes (20-75 mm X 8-20 mm) in approximately 3 months and attach to the intestinal wall of the mammalian hosts. The adults have a life span of about one year. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
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Egg of Fasciolopsis buski. Images reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
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Adult fluke of Fasciolopsis buski. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
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The life cycle of Heterophyes. The adult parasites release embryonated eggs (each with a fully developed miracidium), which are then passed in the host's feces. After ingestion by a suitable snail (first intermediate host), the eggs hatch and release miracidia, which penetrate the snail's intestine. Snails of the genera Cerithidea and Pirenella are important hosts in Asia and the Middle East, respectively. The miracidia undergo several developmental stages in the snail (sporocysts, rediae, cercariae). Many cercariae are produced from each redia. The cercariae are released from the snail and encyst as metacercariae in the tissues of a suitable freshwater or brackish-water fish (second intermediate host). The definitive host becomes infected by ingesting undercooked or salted fish that contains metacercariae. After ingestion, the metacercariae excyst, attach to the mucosa of the small intestine, and mature into adults (measuring 1-1.7 mm X 0.3-0.4 mm). Heterophyes heterophyes infects humans, various fish-eating mammals (eg, cats, dogs), and birds. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
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Life cycle of Metagonimus. The adult parasites release fully embryonated eggs (each with a fully developed miracidium), which are then passed in the host's feces. After ingestion by a suitable snail (first intermediate host), the eggs hatch and release miracidia, which penetrate the snail's intestine. Snails of the genus Semisulcospira are the most common intermediate host for Metagonimus yokogawai. The miracidia undergo several developmental stages in the snail (sporocysts, rediae, cercariae). Many cercariae are produced from each redia. The cercariae are released from the snail and encyst as metacercariae in the tissues of a suitable freshwater or brackish-water fish (second intermediate host). The definitive host becomes infected by ingesting undercooked or salted fish that contains metacercariae. After ingestion, the metacercariae excyst, attach to the mucosa of the small intestine, and mature into adults (measuring 1-2.5 mm X 0.4-0.75 mm). M yokogawai infects humans, fish-eating mammals (eg, cats, dogs), and birds. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
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Various animals may be definitive hosts for different Echinostoma species, such as aquatic birds, carnivores, rodents, and humans. Unembryonated eggs are passed in stool (1), and development occurs in the water (2). The miracidium takes an average of 10 days to mature and then hatches (3), penetrating the first intermediate host, a snail (4). Snails, in general, serve as the first intermediate host. The intramolluscan stages are as follows: sporocyst (4a); rediae (4b); and cercariae (4c). Cercariae may then encyst as metacercariae in the same first intermediate host or leave to penetrate a new second intermediate host (5). Several animals may become the second intermediate host, such as other snails, bivalves, fish, and tadpoles. The definitive host gets infected after eating infected second intermediate hosts (6). The metacercariae excyst in the duodenum (7). Adults then live in the small intestine (8). Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
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Magnified image of Echinostoma spp. egg. Echinostoma eggs resemble F busk and Fasciola eggs, with the latter two only bigger in size. Specimen slides courtesy of the University of the Philippines - College of Public Health, Department of Parasitology.
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Low power magnification (arrow) of a Heterophyid egg. Specimen slides courtesy of the University of the Philippines - College of Public Health, Department of Parasitology.
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Magnified view of a Heterophyid egg. Specimen slides courtesy of the University of the Philippines - College of Public Health, Department of Parasitology.
Tables
Infection |
Source* |
Geographic Distribution** |
|---|---|---|
Fasciolopsiasis |
Freshwater plants (water caltrop, water chestnut) |
Asia and Indian subcontinent, especially in areas where humans raise pigs and consume freshwater plants (as of December 8, 2017) |
Echinostomiasis |
Tadpoles, freshwater snails, fish, frogs |
Worldwide, but human cases seen most frequently in Southeast Asia and in areas where undercooked or raw freshwater snails, clams, and fish are eaten (as of December 27, 2017) |
Heterophyiasis |
Fish |
Egypt, Middle East, Far East (as of January 3, 2018) |
Metagonimiasis |
Fish (cyprinid) |
Far East, Siberia, Manchuria, the Balkan states, Israel, Spain (as of December 29, 2017) |
* Adapted with permission from Tribble D, Wagner KF. Trematode infections. Infectious Disease Practice. 1996; 20:69-73. ** Updated data from the Centers for Disease Control and Prevention (DPDx Laboratory Identification of Parasites of Public Health Concern. Available: http://www.cdc.gov/dpdx/) |
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Infection |
Source |
Clinical Features |
Alaria americana |
Undercooked frog legs |
Disseminated fatal thoracic, gastrointestinal, retroperitoneal, and CNS manifestations; intraocular infections |
Echinostomiasis (16 species) |
Freshwater fish, aquatic plants, clams, snails, mollusks, contact with aquatic birds |
May be asymptomatic; mild abdominal pain, bloating, dyspepsia, diarrhea, eosinophilia |
Fibricola species |
Tadpoles |
Abdominal pain, diarrhea, fever, eosinophilia |
Fasciolopsis species |
Water chestnut, water calthrop, water bamboo, water morning glory lotus and water hyacinth |
May be symptomatic; may be subclinical; gastritis, nausea, diarrhea, eosinophilia; generalized edema in persons with heavy infection burden |
Gastrodiscoides species |
Vegetables, aquatic plants |
Often asymptomatic; may manifest as abdominal pain and diarrhea in severe cases |
Watsonius watsoni |
Water bamboo |
Severe diarrhea |
Fischoederius elongates |
Aquatic plants |
Epigastric pain and vomiting |
Heterophyes species |
Mullets, fish; brackish water |
May be asymptomatic; intestinal mucosal disease, ulcer-related abdominal pain, dyspepsia, nausea, vomiting, diarrhea, weight loss |
Gymnophalloides seoi |
Oysters |
Fever, abdominal pain, anorexia, weight loss, diarrhea, pancreatitis |
Carneophallus brevicaeca |
Shrimp |
Fatal when infection involves CNS and heart |
Brachylaima ruminae |
Poultry, rats |
Abdominal pain, diarrhea |
Metagonimiasis species |
Fish (ayu, golden carp) |
May be asymptomatic; intestinal mucosal disease, ulcer-related abdominal pain, dyspepsia, nausea, vomiting, diarrhea, weight loss |
Nanophyetus salmincola |
Undercooked fish (eg, salmon, trout, steelhead) |
May be symptomatic; mild diarrhea, abdominal pain |
*Adapted from Berger SA, Marr JS. Human Parasitic Diseases Sourcebook. 1st ed. Sudbury, MA: Jones and Bartlett; 2006. |
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