We detected metacercariae of Echinostoma revolutum in Filopaludina sp. Adult flukes were harvested from experimentally infected hamsters at days 14 and 17 post-infection. A total of 37 collar spines were arranged around the head collar, and large excretory granules were seen in 2 canals of the excretory bladder. The day old adult flukes were elongated, ventrally curved, and 5. The head collar had a total of 37 collar spines arranged in 2 alternating rows, including 5 corner spines on each side.
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The trematode family Echinostomatidae includes numerous spiny-collared intestinal flukes known to infect humans. Infections are documented mostly from members of the genera Echinostoma E. Sporadic infections with members of other echinostomid genera including Echinoparyphium , Acanthoparyphium, Artyfechinostomum, Episthmium , Himasthla, Hypoderaeum, and Isthmiophora are known. Like many trematodes, echinostomid flukes undergo a multi-host indirect life cycle.
Unembryonated eggs are passed in feces of infected definitive hosts and develop in water. Miracidia usually take about 3 weeks to mature before hatching , after which they swim freely and penetrate the first intermediate host, a snail.
The intramolluscan stages include a sporocyst stage , one or two generations of rediae , and cercariae , which are released from the snail. The cercariae may encyst as metacercariae within the same first intermediate host or leave the host and penetrate a new second intermediate host. The definitive host becomes infected after eating metacercariae in infected second intermediate hosts. Metacercariae excyst in the duodenum and adults reside in the small intestine for some species, occasionally in the bile ducts or large intestine.
Many animals including birds, carnivores, rodents, and humans may serve as definitive hosts for various echinostomid species. The most frequently encountered zoonotic species, Echinostoma hortense and E. The first intermediate host is always a snail families Planorbidae, Lymnaeidae, and Bulinidae , and the major competent intermediate hosts vary by parasite species.
Also depending on species, several animals may serve as the second intermediate host, including other snails, bivalves, fish, salamanders, and tadpoles. Echinostomes occur in wildlife and domestic animals worldwide, but human cases are seen most frequently in Southeast and East Asia.
Incidence is highest in areas where undercooked or raw freshwater snails, clams, fish, or amphibians are eaten. Pathogenicity likely varies depending on the infecting species. Catarrhal inflammation often occurs due to the penetration of the sharp-spined collar into the intestinal mucosa, which creates ulcerative lesions.
Peripheral eosinophilia is usually present. They have an inconspicuous operculum and the abopercular end is often thickened. The larger eggs are very similar to Fasciola and Fasciolopsis.
Eggs are passed unembryonated in feces. Echinostomid flukes are much longer than wide and measure about 2—10 mm long by 1—2 mm wide, depending on the species.
The oral sucker is surrounded by a collar of spines, the number of which varies among species. The oral and ventral suckers are located fairly close to one another. A single ovary is situated near the large, paired testes. Adults reside in the small intestine of the definitive host. The following images were taken from an adult echinostomid removed from a colon polyp during routine colonoscopy.
Like all trematodes, echinostomids require a snail as a first intermediate host. The second intermediate host may also be a snail, sometimes the same individual snail that served as the first intermediate host.
Due to the large geographic distribution of echinostomes, and the many species present, there are many species of snails that may serve as first or second intermediate hosts. Other second intermediate hosts include bivalves, fish, salamanders, and tadpoles. Diagnosis is based on microscopic identification of eggs in the stool. Because the eggs are large, careful measurements must be taken to avoid confusion with the eggs of Fasciola , Fasciolopsis, and Gastrodiscoides.
Genus- and species-level identification cannot be done based on egg morphology and adults are needed for a definitive diagnosis. More on: Morphologic comparisons with other intestinal parasites. Standard precautions for the processing of stool samples apply. Echinostomid eggs are not infectious to humans. Sah, R. Human echinostomiasis: a case report. BMC Research Notes , 11 1 , p. Toledo, R. An update on human echinostomiasis. DPDx is an educational resource designed for health professionals and laboratory scientists.
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Minus Related Pages. Parasite Biology Image Gallery Laboratory Diagnosis Resources Causal Agents The trematode family Echinostomatidae includes numerous spiny-collared intestinal flukes known to infect humans.
Life Cycle View Larger. Echinostomid egg in wet mounts. Figure A: Echinostomid egg in an unstained wet mount of stool. Image taken at x magnification. Echinostoma spp. Figure A: Adult of E. Figure B: A closer view of the anterior region of the E. Shown here are eggs EG within the size range for Echinostoma spp.
Figure B:Higher magnification of the anterior end of the specimen in Figure A. Notice the acetabulum ventral sucker, AC.
Figure C:Higher magnification of the posterior end of the specimen in Figure A. Notice the vitelline glands VT and lobed testes TE. Intermediate hosts of Echinostomatidae Like all trematodes, echinostomids require a snail as a first intermediate host. Figure A: Lymnaea sp. Figure D: Viviparus sp. This snail genus has been recorded as a second intermediate host for E. Figure B: Radix sp. This snail genus has been recorded as a first intermediate host for Echinostoma Hortense and a second intermediate host for E.
Figure E: Corbicula sp. This bivalve genus has been recorded as a second intermediate host for E. Figure C: Gyraulus sp. This snail genus has been recorded as an intermediate host for E. Laboratory Diagnosis Diagnosis is based on microscopic identification of eggs in the stool.
Morphology More on: Morphologic comparisons with other intestinal parasites Laboratory Safety Standard precautions for the processing of stool samples apply. Suggested Reading Sah, R. To receive email updates about this page, enter your email address: Email Address. What's this? Links with this icon indicate that you are leaving the CDC website. Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website.
Echinostoma revolutum can be found in the snail Lymnaea elodes in North America Serensen et al. Kanev, ; Sorensen, et al. Eggs of Echinostoma revolutum are found in fresh water habitats Kanev, where waterfowl occur. The subsequent life stages are all found in intermediate or definitive hosts, all of which are found in the same still or slow-moving freshwater habitats.
Echinostoma revolutum is a trematode that can be parasitic in humans. It causes the disease echinostomiasis. Echinostoma revolutum is the most widely distributed species of all 20 Echinostomatidae species; it is found in Asia, Oceania, Europe, and the Americas. Echinostomiasis is not only an endemic infectious disease in Asian countries, but also can be imported by overseas travelers from the United States or Europe.
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