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

trematode Trematoda is a Class (biology), class of flatworms known as flukes. They are obligate parasite, obligate internal Parasitism, parasites with a complex biological life cycle, life cycle requiring at least two Host_(biology), hosts. The intermedia ...

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...

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 mammals 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 Unive ...

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 is ...

* 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 cap ...

, 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 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 ...

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 the ...

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) tha ...

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 testoster ...

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 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'', '' 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'' (the pikes). They are typical of brackish water, brackish and fresh waters of the Northern Hemisphere (''i.e.'' holarctic in distribution). They are kno ...

(''Esox lucius''). The definitive hosts are fish-eating mammals such as domestic dogs (''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''; plural, : wolves), also known as the gray wolf or grey wolf, is a large Canis, canine native to Eurasia and North America. More than thirty subspecies of Canis lupus, subspecies of ''Canis lupus'' have been reco ...

''),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 (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 A journal, from the Old French ''journal'' (meaning "daily"), may refer to: * Bullet journal, a method of personal organization * Diary, a record of what happened over the course of a day or other period *Daybook, also known as a general journal ...

'' 9(1): 1–6. .

coyote The coyote (''Canis latrans'') is a species of 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 ecological ni ...

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 habita ...

s (''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 ...

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 ''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 A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. It ...

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, althoug ...

Effects on human health

''M. conjunctus'' causes a disease called

metorchiasis ''Metorchis conjunctus'', common name Canadian liver fluke, is a species of trematode parasite 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 s ...

. 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 as ...

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 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 t ...

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 refere ...

, 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 uses a solid-phase type of enzyme immunoassay (EIA) to detect the presence ...

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 ''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": th ...

, 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, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

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 The ''Canadian Journal of Research'' is a defunct peer-reviewed scientific journal established in 1929 by the National Research Council of Canada. In 1935, it split into 4 subsections, and expanded with another 2 subsections in 1944. In 1951, ea ...

'' 22: 6–16. . * Eaton R. D. P. (1975). "Metorchiasis – A Canadian Zoonosis". ''

Epidemiological Bulletin Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evi ...

'' (National Health and Welfare, Canada) 19: 62–68. {{Taxonbar, from=Q5032083 Plagiorchiida Taxa named by Thomas Spencer Cobbold