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

trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive h ...

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

in the family Opisthorchiidae. It can infect mammals that eat raw fish in North America. The first intermediate host is a freshwater snail and the second is a freshwater fish.

Taxonomy

This species was discovered and described by Thomas Spencer Cobbold in 1860.

Distribution

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

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...

* From Quebec to Saskatchewan * Maine,

Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its capita ...

, 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 (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...

is strongly muscular. The

esophagus The esophagus ( American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to ...

is very short. The intestinal ceca vary from almost straight to sinuous. The acetabulum is slightly oval and weakly muscular. The male has an anterior

testis A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testostero ...

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 intermediate host of ''M. conjunctus'' is a freshwater snail, '' Amnicola limosus''.Chai J. Y., Darwin Murrell K. & Lymbery A. J. (2005). "Fish-borne parasitic zoonoses: Status and issues". ''

International Journal for Parasitology The ''International Journal for Parasitology'' is an international medical journal published for the Australian Society for Parasitology by Elsevier. The journal includes original research articles, reviews, and commentary relating to parasites ...

'' 35(11–12): 1233–1254. . The second intermediate host is a freshwater fish: ''

Catostomus catostomus The longnose sucker (''Catostomus catostomus'') is a species of cypriniform freshwater fish in the family Catostomidae. It is native to North America from the northern United States to the top of the continent. It is also found in Russia in rive ...

'', '' Salvelinus fontinalis'', ''

Perca flavescens The yellow perch (''Perca flavescens''), commonly referred to as perch, striped perch, American perch, American river perch or preacher is a freshwater perciform fish native to much of North America. The yellow perch was described in 1814 by Samu ...

'', 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'' (the pikes). They are typical of brackish and fresh waters of the Northern Hemisphere (''i.e.'' holarctic in distribution). They are known simply as a p ...

(''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 wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

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

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

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

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

''),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'' 19(4): 353–356. . red foxes (''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, the diminutive island fox (''Urocyon littor ...

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. . coyotes (''Canis latrans''), raccoons (''

Procyon lotor The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of ...

''), muskrats (''Ondatra zibethicus''),

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

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 and in the

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

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.

Sashimi is a Japanese delicacy consisting of fresh raw fish or meat sliced into thin pieces and often eaten with soy sauce. Origin The word ''sashimi'' means "pierced body", i.e. " 刺身" = ''sashimi'', where 刺し = ''sashi'' (pierced, stu ...

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 and one of the oldest of its kind. It is also the world's highest-impact academic journal. It was founded in England in 1823. The journal publishes original research articles, ...

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

symptomatic Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showi ...

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 radiation, and when symptoms and signs are first apparent. In a typical infectious disease, the in ...

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

fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...

. High concentrations of

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

s are in blood. Also, higher concentrations of

liver enzyme Liver function tests (LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial thromboplastin tim ...

s 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 was acquired by Harcourt, Brace & World in 1969. Reed Elsevier bought Harcourt in 2000, and Academic Press is now an imprint of Elsevier. Academic Press publishes referen ...

, 130 pp.
page 6
ndash;7.

Diagnosis and treatment

Eggs of ''M. conjunctus'' can be found by stool analysis.

Serologic Serology is the scientific study of serum and other body fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection (against a given mic ...

analysis can be also used - ELISA test for IgG antibodies against antigens of ''M. conjunctus''. Drugs used to treat infestation include

praziquantel Praziquantel (PZQ), 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 sc ...

: 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 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 The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of . ...

, 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 la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...

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