|Drawing of ventral view of Metorchis conjunctus, scale bar is 1 mm|
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 second is a freshwater fish.
This species was discovered and described by Thomas Spencer Cobbold in 1860.
The distribution of M. conjunctus includes:
The body of M. conjunctus is pear-shaped and flat. The body length is 1⁄4–3⁄8 inch (6.4–9.5 mm). It has a weakly muscular terminal oral sucker. 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 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 is elongated or pyriform, and slightly twisted, and situated to the right and behind the ovary.
The eggs are oval and yellowish brown.
The second intermediate host is a freshwater fish: Catostomus catostomus, Salvelinus fontinalis, Perca flavescens, or Catostomus commersoni. Metacercaria of M. conjunctus were also found in northern pike (Esox lucius).
The definitive hosts are fish-eating mammals such as domestic dogs (Canis familiaris), domestic cats (Felis catus), gray wolves (Canis lupus), red foxes (Vulpes vulpes), gray foxes (Urocyon cinereoargenteus), coyotes (Canis latrans), raccoons (Procyon lotor), muskrats (Ondatra zibethicus), American minks (Neogale vision), fishers (Pekania pennanti), or bears. 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. Sashimi from raw Catostomus commersoni was identified as a source for an outbreak in Montreal in 1993. It was the first symptomatic disease in humans caused by M. conjunctus.
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.
Diagnosis and treatment
Effects on animal health
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.
This article incorporates public domain text from the reference
- Hung See-Lü (1926). "A new species of fluke, Parametorchis noveboracensis, from the cat in the United States". Proceedings of the United States National Museum 69(2627): 1–2.
- Price E. W. (1929). "Two new species of trematodes of the genus Parametorchis from fur-bearing animals". Proceedings of the United States National Museum 76(2809): 1–5.
- 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. doi:10.1111/j.1748-5827.1968.tb04678.x.
- 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. doi:10.1016/j.ijpara.2005.07.013.
- 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. PMID 6644936.
- Axelson R. D. (1962). "Metorchis Conjunctus Liver Fluke Infestation in a Cat". Canadian Veterinary Journal 3(11): 359–360. PMID 17421548. PDF.
- 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. doi:10.1016/S0140-6736(96)90342-6
- 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. PMID 9735521. PDF.
- Smith H. J. (1978). "Parasites of red foxes in New Brunswick and Nova Scotia". Journal of Wildlife Diseases 14(3): 366–370. PMID 691132.
- Dick T. A & Leonard R. D. (1979). "Helminth parasites of fisher Martes pennanti (Erxleben) from Manitoba, Canada". Journal of Wildlife Diseases 15(3): 409–412. PMID 574167.
- Dennis J. Richardson; Peter J. Krause (6 December 2012). North American Parasitic Zoonoses. Springer Science & Business Media. p. 86. ISBN 978-1-4615-1123-6.
- Waikagul J. & Thaekham U. (2014). Approaches to Research on the Systematics of Fish-Borne Trematodes. Academic Press, 130 pp., page 6–7.
- "FLUKE, hermaphroditic, infection"., 2 pp., accessed 31 December 2015.
- Watson T. G & Croll N. A. (1981). "Clinical changes caused by the liver fluke Metorchis conjunctus in cats". Veterinary Pathology 18(6): 778–785. doi:10.1177/030098588101800608.
- 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. PMID 4265550.
|Wikimedia Commons has media related to Metorchis conjunctus.|