''Metorchis conjunctus'', common name Canadian liver fluke, is a species of trematode parasite in the family

Opisthorchiidae Opisthorchiidae is a family of digenean trematodes. Opisthorchiidae have cosmopolitan distribution. The most medically important species in the family Opisthorchiidae are ''Clonorchis sinensis'', ''Opisthorchis viverrini'', and '' Opisthorchis ...

. It can infect

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s that eat raw fish in North America. The first

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...

is a

freshwater snail Freshwater snails are gastropod mollusks which live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs ...

and the second is a freshwater fish.

Taxonomy

This species was discovered and described by

Thomas Spencer Cobbold Thomas Spencer Cobbold FRS (26 May 182810 March 1886) was an English biologist. Life He was born at Ipswich, the third son of Rev. Richard Cobbold, author of the ''History of Margaret Catchpole''. After graduating in medicine at the Univers ...

in 1860.

Distribution

The distribution of ''M. conjunctus'' includes: * East Greenland * From Quebec to Saskatchewan * Maine, Connecticut, South Carolina, US

Description

The body of ''M. conjunctus'' is pear-shaped and flat. The body length is . It has a weakly muscular terminal

oral sucker A sucker in zoology refers to a specialised attachment organ of an animal. It acts as an adhesion device in parasitic worms, several flatworms, cephalopods, certain fishes, amphibians, and bats. It is a muscular structure for suction on a host or ...

. No prepharynx is present. The pharynx is strongly muscular. The esophagus is very short. The intestinal ceca vary from almost straight to sinuous. The

acetabulum The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Structure There are three bones of the ''os coxae'' (hip bone) that c ...

is slightly oval and weakly muscular. The male has an anterior testis and a posterior testis. The testes vary from almost round to oval, and may be deeply lobed or slightly indented. No cirrus pouch is found. The seminal vesicle is slender. The ovary is trilobed. The

receptaculum seminis The spermatheca (pronounced plural: spermathecae ), also called receptaculum seminis (plural: receptacula seminis), is an organ of the female reproductive tract in insects, e.g. ants, bees, some molluscs, oligochaeta worms and certain other in ...

is elongated or pyriform, and slightly twisted, and situated to the right and behind the ovary. The eggs are oval and yellowish brown. Metorchis conjunctus 3

Lifecycle

The first

of ''M. conjunctus'' is a

, ''

Amnicola limosus ''Amnicola limosus'', common name the mud amnicola, is a species of very small aquatic snail, an operculate gastropod mollusk in the family Hydrobiidae. Distribution This species is distributed in the Northwest Atlantic Ocean and along the Gulf ...

''.Chai J. Y., Darwin Murrell K. & Lymbery A. J. (2005). "Fish-borne parasitic zoonoses: Status and issues". '' International Journal for Parasitology'' 35(11–12): 1233–1254. . The second intermediate host is a

freshwater fish Freshwater fish are those that spend some or all of their lives in fresh water, such as rivers and lakes, with a salinity of less than 1.05%. These environments differ from marine conditions in many ways, especially the difference in levels of s ...

: '' Catostomus catostomus'', ''

Salvelinus fontinalis The brook trout (''Salvelinus fontinalis'') is a species of freshwater fish in the char genus ''Salvelinus'' of the salmon family Salmonidae. It is native to Eastern North America in the United States and Canada, but has been introduced elsewhere ...

'', '' Perca flavescens'', or ''

Catostomus commersoni The white sucker (''Catostomus commersonii)'' is a species of freshwater cypriniform fish inhabiting the upper Midwest and Northeast in North America, but it is also found as far south as Georgia (U.S. state), Georgia and as far west as New Mexic ...

''. Metacercaria of ''M. conjunctus'' were also found in northern pike (''Esox lucius''). The definitive hosts are fish-eating mammals such as domestic dogs (''Canis lupus familiaris''), domestic cats (''Felis catus''), wolves ('' Canis lupus''),Wobeser G., Runge W. & Stewart R. R. (1983). "''Metorchis conjunctus'' (Cobbold, 1860) infection in wolves (''Canis lupus''), with pancreatic involvement in two animals". ''

Journal of Wildlife Diseases The ''Journal of Wildlife Diseases'' is a peer-reviewed quarterly journal published by the Wildlife Disease Association. The journal publishes research papers, case and epizootic reports, review articles, and book reviews on wildlife disease inves ...

'' 19(4): 353–356. .

red fox The red fox (''Vulpes vulpes'') is the largest of the true foxes and one of the most widely distributed members of the Order (biology), order Carnivora, being present across the entire Northern Hemisphere including most of North America, Europe ...

es (''Vulpes vulpes''), gray foxes (''Urocyon cinereoargenteus''),Mills J. H. & Hirth R. S. (1968). "Lesions Caused by the Hepatic Trematode, ''Metorchis conjunctus'', Cobbold, 1860: A Comparative Study in Carnivora". '' Journal of Small Animal Practice'' 9(1): 1–6. .

coyote The coyote (''Canis latrans'') is a species of canis, canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecologica ...

s (''Canis latrans''), raccoons ('' Procyon lotor''),

muskrat The muskrat (''Ondatra zibethicus'') is a medium-sized semiaquatic rodent native to North America and an introduced species in parts of Europe, Asia, and South America. The muskrat is found in wetlands over a wide range of climates and habitat ...

s (''Ondatra zibethicus''), American minks (''Neovison vision''), fishers ('' Martes pennanti''), or bears.Behr M. A., Gyorkos T. W., Kokoskin E., Ward B. J., MacLean J. D. (1998). "North American liver fluke (''Metorchis conjunctus'') in a Canadian aboriginal population: a submerging human pathogen?" ''

Canadian Journal of Public Health ''Canadian Journal of Public Health'' is a peer-reviewed scientific journal of public health published by the Canadian Public Health Association on a bimonthly basis. It was originally established in 1910 as the ''Public Health Journal'' (), which ...

'' 89: 258–259.
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It can also infect humans. It lives in the bile duct and in the gallbladder.

Effects on human health

''M. conjunctus'' causes a disease called metorchiasis. It has been known to infect humans since 1946. Humans had eggs of ''M. conjunctus'' in their stools, but they were

asymptomatic In medicine, any disease is classified asymptomatic if a patient tests as carrier for a disease or infection but experiences no symptoms. Whenever a medical condition fails to show noticeable symptoms after a diagnosis it might be considered asy ...

. Sashimi from raw ''

'' was identified as a source for an outbreak in Montreal in 1993.MacLean J. D., Arthur J. R., Ward B. J., Gyorkos T. W., Curtis M. A. & Kokoskin E. (1996). "Common-source outbreak of acute infection due to the North American liver fluke ''Metorchis conjunctus''". '' The Lancet'' 347(8995): 154–158. It was the first symptomatic disease in humans caused by ''M. conjunctus''.

Symptoms

After ingestion of fish infected with ''M. conjunctus'', about 1–15 days are needed for symptoms to occur, namely for eggs to be detected in the stool ( incubation period). The acute phase consists of upper abdominal pain and low-grade fever. High concentrations of eosinophil granulocytes are in blood. Also, higher concentrations of liver enzymes are seen. When untreated, symptoms may last from 3 days to 4 weeks. Symptoms of chronic infection were not reported.Waikagul J. & Thaekham U. (2014). ''Approaches to Research on the Systematics of Fish-Borne Trematodes''. Academic Press, 130 pp.
page 6
ndash;7.

Diagnosis and treatment

Eggs of ''M. conjunctus'' can be found by stool analysis. Serologic analysis can be also used - ELISA test for IgG antibodies against antigens of ''M. conjunctus''. Drugs used to treat infestation include praziquantel: 75 mg/kg in three doses per day (the same dosage applies for adults and for children).

Effects on animal health

Watson and Croll (1981) studied symptoms of cats. Prevention includes feeding with cooked fish (not raw fish).Axelson R. D. (1962). "Metorchis Conjunctus Liver Fluke Infestation in a Cat". ''

Canadian Veterinary Journal ''Canadian Veterinary Journal'' is a monthly peer-reviewed scientific journal covering new scientific developments in veterinary medicine. It was established in 1960 and is the official journal of the Canadian Veterinary Medical Association. Accor ...

'' 3(11): 359–360.
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''M. conjunctus'' was found to be a common infection of domestic dogs in Indian settlements in 1973.Unruh D. H., King J. E., Eaton R. D. & Allen J. R. (1973). "Parasites of dogs from Indian settlements in northwestern Canada: a survey with public health implications". '' Canadian Journal of Comparative Medicine'' 37(1): 25–32. . It has been in found in other animals including raccoons,

minks Mink are dark-colored, semiaquatic, carnivorous mammals of the genera ''Neogale'' and '' Mustela'' and part of the family Mustelidae, which also includes weasels, otters, and ferrets. There are two extant species referred to as "mink": the A ...

, and

gray foxes The gray fox (''Urocyon cinereoargenteus''), or grey fox, is an omnivorous mammal of the family Canidae, widespread throughout North America and Central America. This species and its only congener, the diminutive island fox (''Urocyon litto ...

. The prevalence of ''M. conjunctus'' in wolves in Canada is 1–3%. In wolves, ''M. conjunctus'' causes cholangiohepatitis with periductular fibrosis in the liver. It sometimes causes chronic inflammation and fibrosis of the pancreas in wolves.

References

This article incorporates public domain text from the reference

External links

* Cameron T. W. M. (1944). "The morphology, taxonomy and life history of ''Metorchis conjunctus''". '' Canadian Journal of Research'' 22: 6–16. . * Eaton R. D. P. (1975). "Metorchiasis – A Canadian Zoonosis". '' Epidemiological Bulletin'' (National Health and Welfare, Canada) 19: 62–68. {{Taxonbar, from=Q5032083 Plagiorchiida Taxa named by Thomas Spencer Cobbold