Trematodes

Trematodes

1. "flukes"

2. Trematodes are Parasites of?

   • Several Body systems (NOT just the gut!)
     • 1 or more suckers for attachment

3. Most are HERMAPHRODITIC

   • EXCEPTION! : the genus Schistosoma
   • hermaphroditic = possessing both M & F reproductive organs
     • Able to SELF-FERTILIZE (although this is NOT the norm)
       • This isn't always favorable b/c results in LESS genetic variation = bad (most of time)

4. Trematode Life Cycle

   • Almost always AQUATIC!!
   • 2 IHs USUALLY involved
     • 1st IH almost always SNAIL
     • 2nd IH (if used) varies by fluke species
   • Terms in Trematode life cycle:
     • Egg
     • Miracidium
       • develops slowly w/IN egg, then emerges into water
     • Cercaria
       • stage that emerges from snail
     • Metacercaria
       • Found in 2nd IH or on plants
   • Trematode Life Cycle Variations
     • 1 egg
       • 1 MIRAcidium, which penetrates snail
         • MANY cercariae develop inside snail
           • Cercariae penetrate skin (no 2nd IH)
             • Schistosoma spp.
               • "bilharzia" is what Schistosoma is still known by in many parts of world (its earlier disease name)
                 • b/c Dr. Theodore Bilharz discovered the parasite Schistasoma hematobium
           • Cercariae exit snail & infect 2nd IH
             • Become METAcercariae
               • Paragonimus westermani
           • Cercariae exit snail & develop as metacercariae on aquatic vegetation
             • Fasciola hepatica
           • ASEXUALLY!!

5. Human Infection of Trematode

   • Cercarie penetrates skin!!!

6. A few medically relevant flukes

   • Chinese LIVER Fluke
     • Parasite of liver
       • ADULT flukes in human bile ducts provoke chronic inflammation
         • gradual liver dysfunction
           • Chronic infection can lead to
             • Cholangiocarcinoma (bile duct cancer)
     • Where?
       • Asia
       • Resevoirs?
         • All animal resevoirs
           • makes it very difficult to stop
         • has 2 IHs
           • Perpetuation of infection?
             • Cultural Practices
               • Sushi
               • Consumption of raw/pickled fish
           • 1st IH = snail
           • 2nd IH = fish/crustaceans/other animals
     • UNUSUAL ASPECT OF LIFE CYCLE
       • Eggs are EATEN by snail (rather than penetrate snail via skin)
     • Clonorchis sinensis
     • PREVENTION (of human infection of Chinese Liver Fluke):
       • COOK THE DAMN FISH!
     • TREATMENT of CLF
       • control cultural practices
   • Human LUNG Fluke
     • Paragonimus spp.
     • P. Westermani
     • P. africanus
     • Why is the Human Lung Fluke (Paragonimus spp.) still widespread?
       • Consume crabs/crayfish containing LIVE METAcercariae
         • METAcercariae penetrate duodenum & imbed in ab. wall
           • to DIAPHRAGM
             • Enter LUNGS from the "outside in"
           • metacercariae can also wander off course pentrate heart/spinal cord/etc.
         • Clinical sign of infection
           • Hemoptysis (cough up blood)
           • shortness of breath (dyspnea)
           • weight loss
           • chronic cough
           • What major global diseas does this closely resemble?
             • TUBERCULOSIS
       • PREVENTION:
         • COOK the damn crabs/crayfish!
     • Here the mericidium penetrate the snail skin (unlike chinese liver fluke where snail eats (the eggs)
   • Schistosoma spp.
     • Arguably most medically IMPORTANT TREMATODES!!!
       • 3 species of importance
         • S. mansoni
         • S. japonicum
         • S. hematobium
           • account for 2/3 of cases
       • 90% cases: sub-Saharan Africa
       • Rxn to EGGS causes disease (Schistosomiasis)

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