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Trematoda (trematode, fluke)
Includes both sexual forms (schistosomes) & hermaphroditic forms (others). All species that infect humans have an oral sucker through which the digestive tract opens & a ventral sucker used for attachment. Adults vary in length from 1 mm (Metagonimus) to 7 cm (Fasciola gigantica).
Epidemiology:
- eggs are passed into the environment through the feces, urine or sputum depending upon species of trematode
- hermaphroditic forms produce unembryonated operculate eggs (except Clonorchis & Opisthorchis)
- schistosome eggs are not operculated & each contains a mature larvae when passed from the host
- trematode larvae (miracidia) are ciliated & capable of penetrating tissues of its 1st intermediate host, a snail
- each species of trematode uses a particular species of snail as its 1st intermediate host
- free-swimming larvae termed cercariae are produced within the snail
- schistosome cercariae are capable of penetrating human skin directly, causing schistosomiasis
- cercariae of hermaphroditic trematodes encyst on aquatic vegetation or invade tissues of 2nd intermediate hosts such as fish or crabs
- ingestion of encysted larvae (metacercariae) then results in human infection
- most common in South & East Asia
- species most commonly infecting humans:
- Fasciolopsis buski
- Heterophytes heterophytes
- Metagonimus yokogawai
- Echinostoma
Clinical manifestations:
1) symptoms vary depending upon the number of trematodes parasitizing the host
2) adult flukes may cause inflammation, ulceration & mucus secretion at the site of intestinal wall attachment
3) most infections are asymptomatic
4) loose stools, weight loss, malaise abdominal pain may be noted
Laboratory:
1) diagnosis of trematode infection is made by recovery & identification of eggs* in feces, urine, sputum or occasionally tissues
2) direct mounts & formalin-ethyl acetate concentration methods are most useful for recovery of eggs*.
3) flukes* may also be recovered [3]
* images [2,3]
Management:
- 3 doses of praziquantel over 1 day [2]
Related
trematodiasis
Specific
Dicrocoeliidae
Digenea
Echinostomatidae
Fasciolidae
Heterophyidae
Nanophyetus
Opisthorchidae
paramphistomatidae
Schistosomatidae
Troglotrematidae
General
platyhelminth (flatworm)
Properties
KINGDOM: animal
PHYLUM: helminth
References
- Clinical Diagnosis & Management by Laboratory Methods,
19th edition, J.B. Henry (ed), W.B. Saunders Co.,
Philadelphia, PA. 1996, pg 1289-93
- Grimm L
What's Eating You: 12 Common Intestinal Parasites.
Medscape. November 25, 2019
https://reference.medscape.com/slideshow/intestinal-parasites-6010996
- Grim L
You've Got Worms! Common Intestinal Parasites
Medscape. Jan 23, 2023
https://reference.medscape.com/slideshow/intestinal-parasites-6014593