Biology 625
Fall semester lecture note outline

Updated: 24 September 1999

The text below simply represents a crude lecture outline of one of the topics covered in class. It is not meant to substitute for attending lectures or ignoring the textbook. Additional material, including line drawings, kodachromes, and more extensive information on life-cycles and basic biology, will be supplied in the lectures.

TOPIC #10: Order: Opisthorchiformes

  1. Medium to small worms
  2. Testes usually posterior
  3. Cirrus absent
  4. Seminal receptacle present
  5. Eggs passed fully embryonated
  6. Metacercariae in fish

Metorchis conjunctus (family: Opisthorhiidae)

  1. Common name, the Canadian liver fluke
  2. Small or medium in size, 1-6.5 mm long x 1-2.5 mm wide
  3. Eggs tiny, 22-32 x 11-18 micrometers
  4. Life-cycle
    1. Adults in bile ducts or gall bladder. Mink and raccoon are probably the primary hosts.
    2. Embryonated eggs pass out through common bile duct
    3. Eggs eaten by snails, Amnicola limosa
    4. Miricidia migrate to the liver
    5. Sporocyst and redial generations
    6. Cercariae exit snails and can be densely found in warm, shallow waters. Actively penetrate body surface of various fish, especially white suckers (Catostomus commersonii) and Fallfish (Semotilus corporalis). May persist for over one year in these fish.
    7. Metacercariae ingested along with fish and excyst
    8. Flukes migrate up intestine to common bile duct
    9. Adults begin to produce eggs about 1 mo later, and adults may survive for 7 years or more
  5. Hosts and Epidemiology
    1. A variety of fish eating mammals, including carnivores, rodents, and sometimes humans
    2. Restricted to North America, and probably by the range of the snail host. Primarily in the Hudson Bay watershed and St. Lawrence region.
    3. May also occur in NE United States
    4. Prevalence 5-6% in mink in Hudson Bay watershed in Northern Ontario; 1-3% in mink from SW Ontario
    5. May be common in sled dogs fed uncooked fish in northcentral Canada
    6. Human infections from eating raw white sucker. Either native populations eating raw fish, or small outbreaks from eating sushi made from white sucker
  6. Pathology
    1. Proliferation of biliary epithelium
    2. Progressive thickening of bile duct walls
    3. Emaciation and mortality in heavily infected mink and wolves reported
    4. In high density infections, pancreatic ducts may become infected and endocrine/exocrine functions may be distrupted
  7. Diagnosis, Treatment and Management
    1. Characteristic small eggs in feces
    2. Impacts due to this worm are fairly minimal, and only an occasional problem in local areas with heavy reliance on fish and in captive canids fed raw fish

Clonorchis sinensis (syn. Opisthorchis sinensis) (family: Opisthorchiidae)

  1. Adults of the Chinese liver fluke live in bile ducts
  2. Adults are elongate, 8-20 x 1.5-5 mm
  3. Asiatic in distribution, infecting cats, humans, dogs, badgers, mink, etc.
  4. Large, dendritic testes posteriorly that are tandem
  5. Life-cycle
    1. adults in bile ducts, produce up to 4000 eggs per day; live about 6 months
    2. eggs passed in feces fully embryonated
    3. eaten by snails (most common, Parafossarulus manchouricus)
    4. one sporocyst and one redial generation
    5. cercariae with eyespots; when contacts solid object swims upward
    6. attaches to fish epithelium; over 100 species of cyprinids suitable
    7. enters through skin
    8. encysts under scales or in muscle as metacercariae
    9. some crustacea will also support the metacercariae
    10. fish eaten
    11. metacercariae excyst; migrate to common bile duct
  6. Pathology includes erosion of the biliary epithelium. There is also evidence to suggest that this parasite is probably carcinogenic to humans.
  7. Similar species
    1. Amphimerus noverca (syn. Opisthorchis noverca) in canids and swine, occasionally humans, in India
    2. Amphimerus pseudofelineus (syn. Opisthorchis guayaquilensis) reported to occur in in felids and canids, rarely humans, in the Western Hemisphere
    3. Methorchis albidus in fish-eating mammals, sometimes humans, in Northern temperate to arctic regions of Europe and Asia
    4. Metorchis conjunctus is generally restricted to the Hudson Bay watershed in Canada. It is known to infect canids, mustelids (esp. mink), felids, raccoon, the cotton rat, and humans
    5. Opisthorchis felineus (syn. Opisthorchis tenuicollis) in Europe and Asia, and which also uses a variety of mammals as hosts especially felids, other carnivores, and humans. Evidence is not adequate to conclude that this parasite is a cause of cancer.
    6. Opisthorchis viverrini in southeast Asia infects up to 10 million humans. Evidence suggests that this parasite can induce cholangiocarcinoma in humans.
    7. Pseudamphistomum aethiopicum in Africa
    8. Pseudamphistomum truncatum in wildlife and occasionally humans in Europe, central Asia, and India

Cryptocotyle lingua (family: Heterophyidae)

  1. The family Heterophyidae contains many tear-drop shaped flukes, usually living in the intestinal tract of fish eating birds or mammals
  2. Some members of the genus have a muscular genital sac termed a gonotyl near the acetabulum
  3. Life cycle:
    1. intestine of gulls, terns, grebes, herons, dogs, fox, seal, mink, cats, humans
    2. cosmopolitan
    3. acetabulum and most other organs very posteriorly
    4. unembryonated eggs passed in feces
    5. mature in seawater
    6. eaten by periwinkles (Littorina spp.)
    7. at least one redial generation
    8. cercariae exit
    9. penetrate skin of marine fish, causing a "black spot" disease
    10. metacercariae
    11. eaten by definitive host
    12. excyst in gut and matures
  4. Similar species
    1. Heterophyes heterophyes in fish eating mammals in Asia and North Africa; utilize brackish water fish such as mullet for second intermediate hosts
    2. Metagonimus yokogawai in fish eating mammals in Asia; utilizes freshwater trout, other salmonids, and cyprinids, for second intermediate hosts

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