''Metorchis conjunctus'', common name Canadian liver fluke, is a species of

trematode Trematoda is a Class (biology), class of flatworms known as trematodes, and commonly as flukes. They are obligate parasite, obligate Endoparasites, internal parasites with a complex biological life cycle, life cycle requiring at least two Host ( ...

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

in the family Opisthorchiidae. It can infect

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

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 ...

is a

freshwater snail Freshwater snails are gastropod mollusks that 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 t ...

and the second is a freshwater fish.

Taxonomy

This species was discovered and described by

Thomas Spencer Cobbold Thomas Spencer Cobbold Fellow of the Royal Society, 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 1860.

Distribution

The distribution of ''M. conjunctus'' includes: * East

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

* From Quebec to Saskatchewan * Maine,

Connecticut Connecticut ( ) is a U.S. state, state in the New England region of the Northeastern United States. It borders Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the south. ...

, 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. No prepharynx is present. The

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

is strongly muscular. The

esophagus The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...

is very short. The intestinal ceca vary from almost straight to sinuous. The

acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...

is slightly oval and weakly muscular. The male has an anterior

testis A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is Homology (biology), homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of Androgen, androgens, p ...

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 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''.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 fish species that spend some or all of their lives in bodies of fresh water such as rivers, lakes, ponds and inland wetlands, where the salinity is less than 1.05%. These environments differ from marine habitats in many wa ...

: '' Catostomus catostomus'', '' Salvelinus fontinalis'', '' Perca flavescens'', or '' Catostomus commersoni''. Metacercaria of ''M. conjunctus'' were also found in

northern pike The northern pike (''Esox lucius'') is a species of carnivorous fish of the genus ''Esox'' (pikes). They are commonly found in brackish water, moderately salty and fresh waters of the Northern Hemisphere (''i.e.'' holarctic in distribution). T ...

(''Esox lucius''). The definitive hosts are fish-eating mammals such as domestic

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by hunter-gatherers. ...

s (''Canis lupus familiaris''), domestic

cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

s (''Felis catus''), wolves (''

Canis lupus The wolf (''Canis lupus''; : wolves), also known as the grey wolf or gray wolf, is a canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, including the dog and dingo, though gr ...

''),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 inve ...

'' 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 Carnivora, being present across the entire Northern Hemisphere including most of North America, Europe and Asia, plus ...

es (''Vulpes vulpes''),

gray fox 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 (biology), congener, the diminutive island fox ...

es (''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''), also known as the American jackal, prairie wolf, or brush wolf, is a species of canis, canine native to North America. It is smaller than its close relative, the Wolf, gray wolf, and slightly smaller than the c ...

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

muskrat The muskrat or common 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 various climates ...

s (''Ondatra zibethicus''),

American mink The American mink (''Neogale vison'') is a semiaquatic species of Mustelidae, mustelid native to North America, though human introduction has expanded its range to many parts of Europe, Asia, and South America. Because of range expansion, the Am ...

s (''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'' 89: 258–259.
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It can also infect humans. It lives in the

bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. The bile duct is separated into three main parts: the fundus (superior), the body (middle), and the neck (inferior). Bile is requ ...

and in the

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow Organ (anatomy), organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath t ...

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 Asymptomatic (or clinically silent) is an adjective categorising the medical conditions (i.e., injuries or diseases) that patients carry but without experiencing their symptoms, despite an explicit diagnosis (e.g., a positive medical test). P ...

Sashimi is a Japanese cuisine, Japanese delicacy consisting of fresh raw fish or Raw meat, meat sliced into thin pieces and often eaten with soy sauce. Origin The word ''sashimi'' means 'pierced body', i.e., "wikt:刺身, 刺身" = ''sashimi'', whe ...

from raw '' Catostomus commersoni'' 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 ''The Lancet'' is a weekly peer-reviewed general medical journal, founded in England in 1823. It is one of the world's highest-impact academic journals and also one of the oldest medical journals still in publication. The journal publishes ...

'' 347(8995): 154–158. It was the first

symptomatic Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

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 Incubation period (also known as the latent period or latency period) is the time elapsed between exposure to a pathogenic organism, a chemical, or ionizing radiation, radiation, and when symptoms and signs are first apparent. In a typical infect ...

). The acute phase consists of upper abdominal pain and low-grade

fever Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with Human body temperature, body temperature exceeding the normal range caused by an increase in the body's temperature Human body temperature#Fever, s ...

. High concentrations of

eosinophil granulocyte Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. Along wi ...

s 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 Academic Press (AP) is an academic book publisher founded in 1941. It launched a British division in the 1950s. Academic Press was acquired by Harcourt, Brace & World in 1969. Reed Elsevier said in 2000 it would buy Harcourt, a deal complete ...

, 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 The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay is a solid-phase type of enzyme immunoassay (EIA) to detect the presence of ...

test for IgG antibodies against antigens of ''M. conjunctus''. Drugs used to treat infestation include

praziquantel Praziquantel, sold under the brandname Biltricide among others, is a medication used to treat a number of types of parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is used to treat schist ...

: 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'' 3(11): 359–360.
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''M. conjunctus'' was found to be a common infection of domestic dogs in First Nations 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 The raccoon ( or , ''Procyon lotor''), sometimes called the North American, northern or common raccoon (also spelled racoon) to distinguish it from Procyonina, other species of raccoon, is a mammal native to North America. It is the largest ...

, minks, and gray foxes. The

prevalence In epidemiology, prevalence is the proportion of a particular population found to be affected by a medical condition (typically a disease or a risk factor such as smoking or seatbelt use) at a specific time. It is derived by comparing the number o ...

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 Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...

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