Metorchis conjunctus (Cobbold, 1860) Looss, 1899
ETYMOLOGY:Meta = posterior and orchis = testis along with conjunctus = joined
SYNONYMS:Distoma conjunctum Cobbold, 1860; Parametorchis noveboracensis Hung, 1926; Parametorchis intermedius Price 1929; Parametorchis canadensis Price, 1929; Parametorchis manitobensis Allen and Wardle, 1934.
HISTORY: This trematode was originally described using specimens from the biliary ducts of a red fox that died in the Gardens of the British Zoological Society in London. Cameron (1944) examined the taxonomy of the genus Metorchis and stated that he believed there to only be three species: Metorchis conjunctus in North America, Metorchis albidus (Braun, 1893) Looss, 1899 in Europe and around the Mediterranean, and Metorchis felis Hsü, 1934 in Asia (Metorchis felis is considered here as a synonym of Metorchis orientalis Tanabe, 1919.).
GEOGRAPHIC DISTRIBUTION: North America, most reports are from Canada and the northern parts of the United States. Under the name Parametorchis noveboracensis, the parasite was reported from a cat in Ithaca, NY, USA (Hung, 1926), and it has been reported from a dog in South Carolina, USA (Jordan and Ashby, 1957).
LOCATION IN HOST: Bile ducts.
PARASITE IDENTIFICATION: Specimens of Metorchis differ from those of Amphimerus, Opisthorchis, and Clonorchis in that the uterus is more bunched together, "rosettiform," than in Opisthorchis and with branches that encircle the ventral sucker. Metorchis spp. also tend to be broader than the Opisthorchin relatives. The vittelaria of Metorchis are confined to the lateral margins of the body while in the genus Parametorchis, the vittelaria from the lateral sides become confluent anteriorly. In specimens of Pseudamphistomum the posterior end of the body is squared-off giving the ventral surface of the body the appearance of being a pseudo hold-fast structure.
Adult flukes measure from 1 to 6.6 mm in length with widths of 0.6 to 2.6 mm. The oral sucker is about the same size as the ventral sucker. The testes are situated in the third quarter of the body, tandem or slightly oblique, and tend to be round in outline. The eggs are yellowish brown with a distinct operculum and measure 22 to 32 µm long by 11 to 18 µm wide. The eggs contain an embryo when laid.
LIFE CYCLE: Cameron (1944) examined the life cycle using material from Quebec, Canada. The snail hosts include specimens of Anicola limosa. The snail becomes infected when it ingests the egg. The cercaria is about 0.9 mm long, has a tail fin, and eye spots, and a potential life outside the snail of 60 to 72 hours. The cercariae enter and encyst in the muscles of fresh-water fish (the common sucker, Catostomus commersoni), mainly the lateral muscles extending from the dorsal fin to the tail. In experimentally infected cats, eggs were found in the feces beginning 4 weeks after infection, and the flukes have been found capable of living in cats for at least 5 years.
CLINICAL PRESENTATION AND PATHOGENESIS: Watson and Croll (1981) reported the clinical changes in cats experimentally infected with Metorchis conjuntus. Cats given 200 metacercariae did not develop signs of infection, although they did display a marked eosinophilia and increased serum alanine aminotransferase and leucine aminopeptidase levels. In cats give 300 metacercariae, there were significant clinical signs that developed around patency (which in these studies was 17 days after infection). The cats occasionally developed icterus, bloody urine, and severe diarrhea that disappeared and then recurred over the next few months. The eosinophilia became much less obvious in chronic infections. Primary infections did not seem to prevent the establishment of secondary infections with this parasite. Hyperplasia of the biliary epithelium was the main pathology described in naturally infected cats from Ontario, Canada. (Mills and Hirth 1968)
Disease due to natural infections has been described. Axelson (1962) described lesions in the liver and bile ducts of a cat that also presented with lymphoma. Large numbers of flukes were present with around 200 being in the gall bladder. The bile ducts were markedly enlarged with signs of chronic cholangohepatitis. Another case was described by Essex and Bollman (1930) where cirrhosis formed in a 5-year-old Persian cat from Rochester, Minnesota, USA, due to a mixed infection with Opisthorchis pseudofelineus and Metorchis complexus (the photograph of the specimen clearly shows the vitellaria and would indicate that this was actually an infection with Metorchis conjunctus). The cat became emaciated, and developed ascites and jaundice. At necropsy, there was a hard, enlarged, grayish liver, with no nodules of the surface. The walls of the bile ducts were thickened. The bile contained numerous trematode eggs. There was extensive hyperplasia of the entire biliary duct system and few normal hepatic cells in any histologic section of the liver.
TREATMENT: Praziquantel is likely to prove successful in eliminating these trematodes from many treated cases.
EPIZOOTIOLOGY: Other hosts, including the red fox and the wolf, Canis lupus, have been found infected with this parasite (Wobeser et al., 1983). Other hosts include the raccoon, the gray fox, mink, dogs. The range of the parasite seems to be restricted by the range of the snail intermediate host.
HAZARD TO OTHER ANIMALS: Dogs and other fish-eating mammals can also be infected with this parasite.
HAZARD TO HUMANS: Cameron (1944) states that the eggs of this parasite were observed in the feces of a human being in Saskatchewan, Canada.
CONTROL/PREVENTION: Prevent the ingestion of infected raw, dried or pickled fish; these latter methods are not necessarily going to kill the metacercarial stage of the trematode.
Axelson RD. 1962. Metorchisconjuctus liver fluke infestation in a cat. Can Vet J 3:359-360.
Cameron TWM. 1944. The morphology, taxonomy, and life history of Metorchisconjunctus (Cobbold, 1860). Can J Res 22:6-16.
Essex HE, Bollman JL. 1930. Parasitic cirrhosis of the liver in a cat infected with Opisthorchispseudofelineus and Metorchiscomplexus. Am J Trop Med 10: 65-70.
Hung SL. 1926. A new species of fluke, Parametorchisnoveboracensis, from the cat in the United States. Proc US Natl Mus 69:1-2.
Jordan HE, Ashby WT. 1957. Liver flukes (Metorchisconjunctus) in a dog from South Carolina. JAVMA 141:239-240.
Mills JHL, Hirth RS. 1968. Lesions caused by hepatic trematode, Metorchisconjunctus, Cobbold, 1860. A comparative study in carnivora. J small Anim Pract 9:1-6.
Watson TG, Croll NA. 1981. Clinical changes caused by the liver fluke Metorchisconjunctus in cats. Vet Pathol 18:778-785.
Wobeser G, Runge W, Stewart RR. Metorchisconjunctus (Cobbold, 1860) infection in wolves (Canislupus), with pancreatic involvement in two animals. J Wildl Dis 19:353-356.