Other Trematodes

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Other Trematodes
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Fasciola hepatica

• Liver fluke that has a worldwide distribution
• Infections are contracted by eating uncooked
  aquatic plants on which metacercariae have
  encysted
• Sheep and cattle are reservoir hosts, humans
  occasionally infected
• Juvenile worms cause anemia, damage to the liver
  tissue, and may lodge in ectopic locations
• brain or eye
• Adult worms damage the bile ducts and cause
  damage to liver and a loss of food source
• Treat with rafoxanide in humans and domestic
  animals
• Praziquantel is not effective against F. hepatica

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Life Cycle

• adult in bile ducts of definitive host ? eggs in
  feces for 9-10 days ? miracidium ? penetrates
  lymnaeid snail ? sporocyst --produces many mother
  rediae (larval stage) ? each produces many
  daughter rediae ? each produces many cercariae
  which encyst on vegetation to become metacercaria
  ? ingested by definitive host ? juvenile
  penetrates through intestine into coelom, then
  into liver (lives about 2 months in parenchyma ?
  adult in bile ducts

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Fasciola hepatica

• Adult worm up to 30 mm
• This species can be recognized easily by its
  cephalic cone and shoulders

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F. hepatica Eggs

• Unembryonated condition with smooth oval shape
• Relatively small operculum (compared to eggs of
  Paragonimus westermani), which is most easily
  seen in the bottom picture, where it has
  partially opened due to the pressure of the
  coverslip
• Usually yolk granules completely fill the
  immature egg

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Fasciolopsis buski

• Common to humans and pigs in the Orient
• Lives in the small intestine of definitive host
  rather than in liver
• No cephalic cone or shoulders
• Small oral sucker
• Life cycle is similar to F. hepatica, snails act
  as intermediate host
• Cercaria encyst on plants such as lotus, bamboo
  or water chestnuts and metacercaria swallowed
  when are eaten raw or without washing
• Causes problems with the digestive tract and
  often diarrhea is symptomatic
• Prevent spread by immersing the vegetables into
  boiling water for a few seconds to kill
  metacercaria

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Fasciolopsis buski

• Adult worm up to 75 mm in length

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Clonorchis sinensis

• Liver fluke contracted in Asia by eating
  uncooked freshwater fish in which metacercariae
  have encysted
• May be infected outside the typical area by
  eating imported fish
• Liver tissue is not invaded but heavy infections
  may cause such damage to the bile ducts that
  jaundice, hepatomegaly, ascites, and death occur
• Eggs are found in the feces that gets into the
  water to be eaten by snails and fish (primary and
  secondary intermediate hosts respectively)

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Life Cycle

• adult in bile ducts of definitive host ? eggs in
  feces ? eaten by Parafossarulus snail (1st
  intermediate host) ? miracidium that penetrates
  the gut ? sporocyst which produces many rediae ?
  each produces many cercariae which penetrates
  freshwater fish (2nd intermediate host) ?
  metacercaria ingested by definitive host ?
  juvenile --migrates up bile duct ? adult

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C. sinensis

• Adult worm up to 25 mm
• Treat with praziquantel, drug of choice

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C. sinensis Eggs

• Top row photographed at the same magnification as
  eggs of other species
• The small size of this egg is a key diagnostic
  feature
• Second and third rows photographed at a higher
  magnification, to show the operculum sitting in a
  rim, and a fully formed miracidium, which does
  not hatch from the egg until ingested by a snail
• A small abopercular knob is visible on some eggs

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Paragonimus westermani

• Widely prevalent species in Asia and Oceana
• Lung fluke, encapsalated in pairs by layers of
  granuloma
• Eggs usually cannot leave the lungs, those that
  do, can move up and out by the ciliated
  epithelium, swallowed and voided in the feces
• Humans are probably a lesser source of eggs than
  other mammals
• Eat raw or undercook crustaceans, contamination
  of fingers during preparation, etc
• Pulmonary cases have difficulty breathing,
  chronic cough and sputum with blood and brown
  streaks of eggs
• Diagnosis is by eggs in the sputum or lung
  fluids, seroimmunological tests
• Drug of choice is praziquantel

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Life Cycle

• adult in lungs of definitive host ? eggs in
  sputum or feces ? 2 wks in water to develop into
  miracidium ? penetrates thiarid snail (1st
  intermediate host) ? sporocyst produces many
  mother rediae ? each produces many daughter
  rediae ? each produces many cercariae ? penetrate
  freshwater crab (2nd intermediate host) ?
  metacercaria ingested by definitive host ?
  juvenile penetrates through intestine into
  coelom, then through diaphragm into lung ? adult

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Paragonimus westermani

• Adult worm up to 12 mm long

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P. westermani Eggs

• Found in human sputum, but also occurs in feces
  when swallowed
• Thick abopercular wall
• Unembryonated condition
• Relatively wide operculum (compared to eggs of F.
  hepatica), which sits in a rim

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Metacercariae

• Encysted stages occur in the life cycle of nearly
  all trematodes except for the schistosomes
• F. hepatica, found on the surface of aquatic
  plants, e.g., watercress
• P. westermani, from the muscle of infected crab.