Trematode Parasites of HumansAnimals

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Trematode Parasites of Humans/Animals

• Fasciolopsis buski intestinal fluke
• Fasciola hepatica sheep liver fluke
• Clonorchis sinensis human liver fluke
• Paragonimus westermani - lung fluke
• Paragonimus mexicanii - mexican lung fluke
• Schistosoma mansoni - blood fluke
• Schistosoma haematobium -blood fluke
• Schistosoma japonicum blood fluke
• Avian Schistomes -avian blood flukes

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Trematode Life Cycle - Principles

• Definitive Hosts
• Most mammals including humans can serve as the
  definitive host for various trematode/flukes.
• Flukes generally settle into a given organ/tissue
  and are frequently named by that organ, ie. Liver
  fluke, Lung fluke, Blood Fluke, etc
• Flukes are moneocious and achieve sexual
  maturity in their definitive hosts unlike
  cestode, they cross-fertilize
• Fertile ova from the sexually mature fluke must
  reach a portal of exit, ie. GI Tract, etc
• Intermediate Host
• All flukes utilize freshwater snails as their
  intermediate hosts
• The larvae (called a miracidium) which hatch
  from ova penetrate into the tissues of
  freshwater snails and go through a development
  cycle in the snail
• Immature flukes called cercariae emerge from
  the snail, and find a new definitive host through
  some aquatic mechanism specific to that fluke,
  ie. Skin, Aquatic Plants, Fish

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Fasciola hepatica - sheep liver fluke

• Definitive Host Sheep, Herbivores and Humans
• Resides in the liver esp biliary ducts Ova exit
  in the bile to the intestines
• Intermediate Host freshwater snails
• Symptoms fever, chills, right upper quadrant
  pain which radiates to the scapula, jaundice,
  liver enlargement eosinophilia
• Often cause biliary obstruction and portal
  cirrhosis
• Epidemiology- ova from definitive host deposited
  in freshwater
• Miracidia develop in snails and emerge as
  cercariae
• Metacercariae encyst on watercress
• Humans consume the cercariae while eating
  watercress
• Diagnosis ova are observed in the feces of the
  definitive host

4
Fasciolopsis buski- human intestinal fluke

• Definitive Host Human
• Attach to the bowel wall of the jejunum and
  duodenum
• Intermediate Host - snails
• Symptoms abdominal pain similar to duodenal
  ulcer cause by inflammation and ulceration of
  the intestinal wall
• eosinophilia
• Epidemiology ova in feces deposited in
  freshwater
• Miracida go through cycle in snails releasing
  cercariae
• Metacariae encyst on freshwater vegetation like
  bamboo shoots and water chestnuts which are
  consumed as food
• Cercariae are ingested with aquatic vegetation
• Diagnosis ova are observed in the feces

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Clonorchis (Opisthorchis) sinensis

• Definitive Host dog, cats, and humans
• Adult worms reside in the biliary ducts of the
  liver
• Intermediate Host freshwater snails
• Symptoms same a Fasciola
• Epidemiology cercariae emerge form snails and
  penetrate into the tissues of freshwater fish
  humans and animals that consume raw freshwater
  fish ingest these cercariae
• Diagnosis ova in the feces exit via the bile
  to the intestine

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Paragonimus westermani - lung fluke

• Definitive Host many wild mammals humans are
  accidental hosts
• Sexually mature worms reside in the lungs
• In humans, larvae may migrate into other body
  regions
• Larvae must move from intestine to lungs via
  peritoneal cavity and diaphragm
• Intermediate Host freshwater snails
• Symptoms pulmonary inflammation causes fever,
  cough, and bloody sputum sometimes resembles
  tuberculosis
• Epidemiology ova in feces are deposited in
  freshwater
• Miracida go through developmental cycle in snails
  and emerge as cercariae
• Metacercariae encyst within tissues of freshwater
  crayfish or crabs
• Ingestion of poorly cooked crustecans transmitted
  cercariae
• Diagnosis- ova in sputum or feces

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Paragonimus mexicanii - mexican lung fluke

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology only lung fluke endemic in western
  hemisphere
• Generally acquired through ingestion of poorly
  cooked crayfish
• Diagnosis

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Blood Flukes - Schistosomes

• Characteristics schistosomes are the only
  diecious trematodes
• Adult flukes reside within the large vessels of
  the definitive host
• Male worm is much smaller than female and resides
  within a ventral grove of the female body cavity
• Definitive Hosts most mammals including humans
  and many birds especially migratory water fowl.
• Intermediate Hosts freshwater snails
• Symptoms varies with the location of the worms
• Epidemiology metacercariae emerge from snails
  they are the only fluke cercariae which have a
  tail to enhance motility
• Metacercariae penetrate through skin immersed in
  freshwater
• Diagnosis ova in urine or feces depending on
  the species
• Schistosoma mansoni ova in the stool
• Schistoma japonicum ova in the stool
• Schistoma haemotobium ova in the uine

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Avian Schistosomes - Concepts

• Trematodes reside within the large vein
  surrounding the intestines ova are deposited
  into vascular wall and penetrate through the
  vessel into/and thru the intestinal wall
• Ova exit in bird feces into freshwater streams
  and reservoirs with the U.S. and World
• Miracidia go through cycle in freshwater snails
  and release motile metacercariae into the water.
• Metacercariae penetrate skin of new hosts
• Since humans are not specific hosts larvae
  cannot enter the blood vessels of human Thus,
  they remain in the tissues where they burrow
  subcutaneously forming channels of inflammation.
• The swelling and itching associated with this
  inflammation in humans has been known as
  swimmers itch