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Intestinal Flukes Workup

  • Author: Joseph Adrian L Buensalido, MD; Chief Editor: Michael Stuart Bronze, MD  more...
 
Updated: Jul 14, 2016
 

Laboratory Studies

Stool examination to visualize the ova or adult worms is the diagnostic method of choice.

Other laboratory findings include anemia and eosinophilia.

Serologic tests have limited application; however, for certain combinations of pathogens and their available diagnostic testing, serodiagnosis may be helpful, as in the case of F buski infections.[33]

Chronic fascioliasis is generally evaluated with fecal egg counting after concentration of the eggs in the stool sample via a zinc sulphate floatation method. However, using the sedimentation technique to concentrate the eggs is said to improve sensitivity. A F hepatica coproantigen enzyme-linked immunoassay (ELISA) has been introduced and studied in cattle and sheep. It more accurately reflects the presence of flukes in the host bile ducts in late prepatent infections and clearance of the flukes after treatment.[34] It can probably be used in humans in the future.

Urine assay, particularly of O viverrini excretory-secretory (ES) antigens in urine, has been used to detect O viverrini in Thailand. It was found easier to use and more sensitive than the traditional ethyl-acetate concentration technique.[35]

Diagnosing O viverrini infection via conventional stool examination is difficult, both because the infection may decrease in intensity after repeated treatments under control programs in endemic areas and because of the presence of coinfections with intestinal flukes. Thus, one study has examined a coproantigen sandwich ELISA using recombinant O viverrini cathepsin F (rOv-CF) that uses chicken immunoglobulin Y (IgY) raised against rOv-CF in combination with rabbit immunoglobulin G (IgG) antibody to the somatic O viverrini antigens. This test showed a sensitivity and specificity of 93.3% and 76.7%, respectively, in the detection of opisthorchiasis. The investigators found that it had a positive predictive value (PPV) and negative predictive value (NPV) of 66.7% and 95.2%, respectively, making it a promising test in endemic areas.[36]

The current criterion standard of diagnosis is the formalin ethyl-acetate concentration technique (FECT), performed with fecal samples. However, this test has difficulty detecting light O viverrini infections since the eggs may be confused with eggs of other minute intestinal flukes in stool.[35]

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Other Tests

Merthiolate, iodine, formalin method

The merthiolate, iodine, formalin (MIF) method is used to detect intestinal fluke parasites.

The MIF method was established early as a versatile and accurate technique for identifying intestinal protozoa in stool and fecal samples.[37] The technique simultaneously preserves and stains stool specimens, which can then be examined with direct smear techniques.[38]

Following the development of a concentrated MIF technique, the sensitivity of positively identifying F buski, Heterophyes species, and Echinostoma species in stool specimens was increased.[39] This newly concentrated MIF technique involves the application of a concentration step to the stool specimen before preservation in MIF solution.

Polymerase chain reaction

Various polymerase chain reaction (PCR) methods have shown potential in detecting intestinal fluke parasites. These methods take advantage of the different types of DNA nucleotide sequence variations demonstrated by the different species of parasites within a particular genus.[40]

Polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP)[16] and simple sequence repeat anchored PCR[41] have been reported to be useful in distinguishing among species of the Metagonimus genus (including M yokogawai). These methodologies are based on differences in restriction fragment length polymorphisms and simple sequence repeats among the species. Information derived from RFLP involving specific sites in ribosomal RNA and mitochondrial cytochrome oxidase I (mtCOI) genes may help to differentiate M yokogawai from other Metagonimus species.[42]

Six species of the genus Heterophyidae were reported to be distinguished with PCR assays developed based on variations in rDNA polymorphisms among the species.[43]

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Contributor Information and Disclosures
Author

Joseph Adrian L Buensalido, MD Clinical Associate Professor, Section of Infectious Diseases, Department of Medicine, Philippine General Hospital, University of the Philippines Manila College of Medicine

Joseph Adrian L Buensalido, MD is a member of the following medical societies: American Society for Microbiology, Infectious Diseases Society of America, Philippine Medical Association, Michigan Infectious Disease Society, Philippine College of Physicians

Disclosure: Nothing to disclose.

Coauthor(s)

Marja Arcangel Bernardo, MD Fellow, Section of Infectious Diseases, Department of Medicine, University of the Philippines-Philippine General Hospital

Marja Arcangel Bernardo, MD is a member of the following medical societies: Philippine College of Physicians

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Association, Oklahoma State Medical Association, Southern Society for Clinical Investigation, Association of Professors of Medicine, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

Chi Hiong U Go, MD Assistant Professor, Department of Internal Medicine, Texas Tech University Health Science Center at Odessa

Chi Hiong U Go, MD is a member of the following medical societies: American College of Physicians-American Society of Internal Medicine

Disclosure: Nothing to disclose.

Thomas E Herchline, MD Professor of Medicine, Wright State University, Boonshoft School of Medicine; Medical Director, Public Health, Dayton and Montgomery County, Ohio

Thomas E Herchline, MD is a member of the following medical societies: Alpha Omega Alpha, Infectious Diseases Society of Ohio, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Burke A Cunha, MD Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital

Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Asim A Jani, MD, MPH, FACP Clinician-Educator and Epidemiologist, Consultant and Senior Physician, Florida Department of Health; Diplomate, Infectious Diseases, Internal Medicine and Preventive Medicine

Asim A Jani, MD, MPH, FACP is a member of the following medical societies: American Association of Public Health Physicians, American College of Physicians, American College of Preventive Medicine, American Medical Association, American Public Health Association, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Paul Chen University of Texas Southwestern Medical School

Disclosure: Nothing to disclose.

Acknowledgements

The author would like to acknowledge Paul Chen, BS, ScM (2008) in Genetic Epidemiology, Johns Hopkins University Bloomberg School of Public Health, whose contributions and insights were invaluable for the revision of this article.

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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.
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.
Egg of Fasciolopsis buski. Images reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
Adult fluke of Fasciolopsis buski. Image reproduced from the Division of Parasitic Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, GA.
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.
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.
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.
Table 1. Common Intestinal Trematode Infections*
Infection Source Geographic Distribution
Fasciolopsiasis Freshwater plants (water caltrop, water chestnut) China, Thailand, Bangladesh, India
Echinostomiasis Tadpoles, freshwater snails, fish, frogs Indonesia, Philippines, Taiwan, Thailand
Heterophyiasis Fish Egypt, Iran, Tunisia, Turkey
Metagonimiasis Fish (cyprinid) Far East, Spain, Eastern Europe
*Adapted with permission from Tribble D, Wagner KF. Trematode infections. Infectious Disease Practice. 1996;20:69-73.
Table 2. Commonly Associated Exposures and Clinical Features of Certain Intestinal Trematodes*
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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