2705466
| Question | Answer |
| Trematodes | Phylum PLATYHELMINTHES Dorsally flattened 1.1 billiom people worldwide at risk from food borne trematode infections Particularly in SE asia amd westerm pacific region |
| Opisthorchis (clonorchis) sinensis ABOUT | 20-30m people infected ww 2cm adult length Main foci: SE Asia, japan, korea, thailand, china Causes OPISTHORCHIASIS Causes diarrhoea and abdominal pain |
| Fasciola hepatica ABOUT | Largely a parasite of livestock 2.4-17m people infected Ww distribution: Bolivia, portugal, iran, france, egypt Occurs in bile duct Plant based |
| Paragonimus westermani ABOUT | 21m people infected Occurs in Asia (china, korea, india, japan, phillipines, sri lanka, taiwan, thailand, vietnam) central west africa, s america Adult 8-16mm in length |
| Schistosomes ABOUT | 200m infected Blood fluke Live in blood vessels in specific sites in body America, asia, s.america |
| Types of schistosomes | Schistosoma mansoni (intestinal) Schistosoma japonicum (intenstinal) Schistosoma haemotobium (urinary) |
| Opisthorchis sinensis lifecycle | Human eats raw or undercooked fish infected with METACERCARIAE Excysts in the duodenum within 3-4 weeks Migrates to biliary duct and becomes adult Human defecates fully developed and embryonated eggs (requires freshwater) Snails ingest eggs (bithynia spp) Inside snail, eggs release miracidia which penetrate intestinal wall amd sporocysts develop within haemocoel cell Rediae then develop within 17 days and wthin 30 days, the ciliated cercariae are released. CERCARIAE penetrate 2nd intermediate host - cyprinid fish (carp) Encyst on skin or flesh and turn into METACERCARIAE |
| Paragonimus westermani LIFE CYCLE | Humans ingest inadequately cooked or pickled crustaceans containing METACERCARIA Excyst in duodenum Penetrate through intestinal wall Then enters diaphragm via thoratic cavity Excreted unembryonated in sputum by being spat out Or swallowed and passed out in stool Eggs become embryonated and hatch in 7-21 days to release MIRACIDIUM Miracidia hatch and seek first intermediate host, a semisulcospira snail species Approx 1 month in snail Sporocysts -> redia -> daughter redia -> cercariae Penetrates heart and muscle of second intermediate host crustacean (crab or crayfish) Cercariae invade crustaceam amd encyst into metacercariae. Infective after 23 days |
| Fasciola hepatica LIFECYCLE | Human or ruminant ingests infective metacercariae Metacercariae resistant to stomach ph Excysts in small intestine wall and migrates to liver Takes about 7 days Excysts in duodenum, migrates through intestinal wall Burrows through bowels to reach bile duct Matures into adult in biliary duct, where it can live for 25 years Unembryonated eggs passed in feces Become embyonated in water Eggs release MIRACIDIA penetrate and invade a snail IM host Undergoes several developmental stages in snail Sporocyst-> reduae-> occasional daughter rediae if if emviro conditions are adverse -> optimal contion 10 degrees reached, CERCARIAE Reased 5-6 weeks after infectiom and encysts in water plants (mint or watercress) Developes into METACERCARIAE and infects host |
| Natural/manmade water bodies | IRRIGATION SYSTEMS DAMS |
| Irrigation schemes | Brings water into fields flooding and aiding transmission F.hepatica require vegetation for metacercariae to develop on If IS werent utilised, it would prevent cercariae from moving from mollusc host |
| Dams | Building w/o proper planning allows snails to populate the water = host Concerns in china over 3 gorges dams causing an increase in f-b-t infections Fish and crustaceans occur in close proximity to snails = hosts Prope planning would prevent miracidia from infecting |
| Water conditions | Velocity Temperature Soil conditions Water current Water quality Important roles in formation of suitable habitats Some trematodes prefer polluted water (min ho, 2004) F.hepatica require clean weater |
| Night soil | Problematic May contain trematode eggs Prevent usage of night soil, prevent transmission |
| What requires aquatic transmission? | Mollusc Fish Crustacean Metacercariae Unembryonated egg |
| A study found | A 2.15 rold increase in f.b.t. Inf tiom when freshwater bodies are in close proximity to house |
| Schistosoma LIFECYCLE | SWIMMERS ITCH CERCARIAE penetrates human skin and loses its forked tail, becoming a SCHISTOSOMULAE Migrates to blood in liver and matures into adult Paired adults migrate to bowel and female deposits eggs Shed i human feces, or urine Eggs hatch and release MIRACIDIA Pentrate snail 2 generations of sporocysts Free oiving in water Turn into infective CERCARIAE |
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