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Parasitology 101 is an educational blog that that can be used as a study guide for microbiology, infectious disease and medical technology students. The “bullet-point” format keeps the information concise and to the point.

F. buski egg/CDC

F. buski egg/CDC

General Information

  • Human intestinal trematodiases are associated with eating habits
  • They are localized to areas where there is water, snail vectors and reservoir hosts
Geography
 
  • Widely found in rural southeast Asia, in particular central and south China, parts of India and Thailand
Morphology (adults)
 
  • Fasciolopsis buski is the largest fluke to infect humans, aka Giant Intestinal Fluke
  • 7.0 x 1.5 cm
  • Large, leaf-shaped, lacks a cephalic cone
Morphology (eggs)
 
  • Large, thin-shelled, unembryonated, operculated
  • 130-150 x 78-98 um
  • Found in large numbers in feces, too similar to F. hepatica to differentiate
Life Cycle
 
  • Adults in the small intestine
  • Eggs pass in feces to water where they embryonic
  • After few weeks, miracidium emerges
  • Miracidium swims to find suitable snail (Segmentina sp.) as first intermediate host
  • In the snail-sporocysts>rediae>cercariae
  • Cercariae released from snail to water
  • Encyst on aquatic plant as metacercariae
  • Plant eaten raw by mammalian host (humans and pigs)
  • Metacercariae excysts and attach to the gut mucosa
  • Develop into adults in about 3 months
  • Lives for one year

Pathology

  • More worms, more disease- usually asymptomatic
  • Large number of worms attaching to mucosa – bleeding, inflammation and ulceration
  • Diarrhea (foul smelling greenish-yellow stools), abdominal pain, intestinal obstruction, edema
  • Toxic products from worms may be absorbed and cause toxemia
  • Death is rare

Diagnosis

 
  • Travel history
  • Demonstration of eggs in feces or vomit (eggs indistinguishable from F. hepatica)
  • Rarely by identifying adult fluke
Treatment
 
  • Praziquantel is the drug of choice
Epidemiology
 
  • Pigs are reservoir hosts
  • Metacercariae encysts on hard surface, particularly water plants like water caltrop and water chestnuts
  • The outer cover of plant is peeled off with teeth and metacercariae are released into the mouth
  • Children more frequently infected–eat water plants going to and from school
Prevention
 
  • Treatment
  • Education
  • Changing eating habits- do not eat without boiling first
  • Keep pigs from contaminating areas where water plants grow
  • Do not feed water plants to pigs

Related: Diphyllobothrium latum

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