Intestinal Flukes Workup
- Author: Joseph Adrian L Buensalido, MD; Chief Editor: Michael Stuart Bronze, MD more...
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.
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. 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.
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.
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.
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. The technique simultaneously preserves and stains stool specimens, which can then be examined with direct smear techniques.
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. 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.
Polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) and simple sequence repeat anchored PCR 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.
Six species of the genus Heterophyidae were reported to be distinguished with PCR assays developed based on variations in rDNA polymorphisms among the species.
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|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.|
|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.|