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Trematodes/flukes 

  • Leaf-like, unsegmented flat worms
  • No body cavity
  • Incomplete alimentary tract
  • Have varying habitat in definitive hosts
A. Schistosomiasis  
  1. Blood fluke 
  2. Bilharziasis
  1. Five main species infect humans
    1. S. mansoni      :       eggs with lateral spine
    2. S. haematobium      :      eggs with terminal spine
    3. S. intercalatum        :       eggs with terminal spine                     
    4. S. japonicum           :        round eggs with lateral knob
    5. S. mekongi              :       round eggs with minute spine
  2. Only S. haematobium found in India (gimvi area of Maharashtra)
  3. Definitive host-man
  4. Intermediate host-snail
  5. All schistosomes share basic life cycle
  6. Eggs passed in urine (S. haematobium), feces (S. japonicum, S. mansoni, S. intercalatum)→ eggs contain miracidium→ hatch in water→ miracidium penetrate fresh water snail→ develops into mother sporocyst→ daughter sporocyst→ cercariae→ released in water→ penetrate the skin of humans→ schistosomula→ lymphatics/ venous vessels→ lungs→ portal vessels (all species migrate to mesenteric veins except S. haematobium which migrates to vesicle plexus)→ develop into adults→ mate→ eggs
1.  Clinical features:
  1. Cercarial dermatitis
  2. Acute schistosomiasis (katayama fever): S. mansoni, S. japonicum
  3. Chronic intestinal schistosomiasis: S. mansoni, S. japonicum, S. intercalatum, S. mekongi (abdominal pain, dysentery, obstruction, hepatosplenomegaly, portal hypertension)
  4. S. hematobium: hematuria, dysuria, urgency, frequency, squamous cell carcinoma
  5. Ectopic schistosomiasis: eggs reach uncommon location (CNS, S. japonicum)
2.  Laboratory diagnosis:
  1. Fecal specimen: eggs                              
  2. Urine specimen: eggs
  3. Biopsy (liver, rectal, bladder): eggs                  
  4. Serology: IFAT, ELISA

B. Fasciola Hepatica/Liver flukea.  Mode of infection: ingestion of aquatic vegetation contaminated with encysted metacercaria
  1. Definitive host: sheep, goat, cattle
  2. Intermediate host: 1st: snail, 2nd:aquatic vegetattion
  3. In sheep eggs laid in the biliary tract→ feces→ miracidium hatches from egg→ penetrates snail→ sporocyst→ rediae → cercariae → cercariae emerge from snail→ encyst on aquatic vegetation (metacercariae)→ ingested by definitive host→ excyst in duodenum→ penetrate intestinal wall→ penetrate liver→ reach bile duct→ develop into adult→ mating→ eggs
1.  Clinical features:
  1. Epigastric pain, fever, diarrhea, jaundice, urticaria (dermographism), arthralgia, eosinophilia
  2. Acute fascoliasis: tender hepatomegaly, fever, eosinophilia
  3. Chronic: obstruction/ inflammation of bile duct
2.  Laboratory diagnosis:
  1. Eggs: feces
  2. Serology: ELISA, CFT, LA, IHA, IFAT
C.  Paragonimus westermanii /Lung flukea.  Mode of infection: ingestion of raw/ undercooked crab/ crayfish
  1. Life cycle:
  2. Definitive host: man, tiger, leopards
  3. First intermediate host: fresh water snail
  4. Second intermediate host: fresh water crab, crayfish
  5. Eggs reach brochioles→ coughed up→ swallowed→ passed in feces→ miracidium hatch in water→ penetrate snail→ sporocyst→ rediae→ cercariae→ emerge from snail→ penetrate crab/ cray fish→ encyst (metacercariae) in gills/ muscles→ ingestion of raw/ undercooked intermediate host→ excyst in duodenum→ young worms penetrate through gut wall→ penetrate diaphragm→ penetrate lung capsule→ develop into adult worm→ mating→ eggs
1.  Clinical features:
  1. Chronic cough, hemoptysis (endemic hemoptysis), pleural pain, dyspnoea, secondary bacterial infection
2.  Laboratory diagnosis:
  1. Sputum, stool: eggs
  2. Serology: ELISA, CFT
D. Clonorchis sinensis/Chinese liver flukea.  Mode of infection: ingestion of raw/ undercooked fresh water fish
  1. Life cycle:
  2. Definitive host: man, dog, pig, cat
  3. First intermediate host: fresh water snail
  4. Second intermediate host: fish
  5. Eggs containing miracidium from bile duct to intestine→ excreted in feces→ miracidium hatch in water→ penetrate snail→ sporocyst→ rediae→ cercariae→ emerge from snail→ penetrate beneath the scales of fish→ encyst (metacercariae) in subcutaneous tissue→ ingestion of raw/ undercooked fish→ excyst in duodenum→ young worms migrate up the bile duct→ develop into adult worm→ mating→ eggs
1.  Clinical features: cholangitis, portal hypertension, biliary obstruction, implicated in cholangiocarcinoma

2.  Laboratory diagnosis:
Eggs: stool examination, enterotest

List of bile stained eggs

  1.  Ascaris lumbricoides
  2. Trichuris trichiura
  3. Taenia solium, Taenia saginata
  4. Echinococcus granulosus
  5. Diphyllobothrium latum
  6. Clonorchis sinensis
  7. Paragonimus westermanii
  8. Fasciola hepatica
  9. Fasciolopsis buski
  10. Schistosoma haematobium, Schistosoma mansoni, Schistosoma japonicum




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