cestodes

• tapeworms = cestodes
• beef tapeworm = Taenia solium
• pork tapeworm = Taenia saginata
• dog tapeworm = Echinococcus granulosus
• definitive host is


  an organism which supports the adult or sexually reporoductive form of a parasite
• intermediate host is 


  an organism that supports the immature of non-reproductive forms of a parasite
• tapeworms characteristics

  • beef 4-12m
  • pork 4-8m
  • dog 3-6mm
  • dorso-ventrally flattened
  • scolex is anterior attachment organ
  • strobila is segmented part of body plan (long chain of proglottids)
  • no gut
  • tegument (body wall) is metabolically active
• scolex 


  attachment organ with suckers and sometimes hookers
• strobila is chain of proglottids
• proglottids 


  grow continuously from neck, new replace old
• proglottids go from 


  immature to mature to gravid
• T.solium has 


  4 large suckers and rostellum (double row of hooks)
• T.saginata has 


  4 large suckers and no rostellum
• proglottid is monoecious so contains 


  both male and female sex organs
• fertilisation can occur between same or different proglottids
• nutrition

  • specialised membrane transport system with tegument
  • attachment function to get nutrients
  • microvillous projections
• excretion

  • flame cells (beat cilia)
  • generate current to force nitrogenous waste to exit into tubule
  • allows tapeworms to conserve water and eliminate salts
• pork and beef tapeworm life cycle

  • humans infected by ingesting raw/under-cooked infected meat
  • eggs or gravid proglottids in faeces passed onto environment
  • castle and pigs ingest from vegetation
  • oncospheres hatch, penetrate intestinal wall, circulate to muscles
  • oncospheres develop into cysticerci in muscle
• no adult tapeworm in pigs or cattle
• eggs ingested by intermediate host, contain larval stag (oncosphere)
• embryophore is thick membrane that forms 


  highly protective structure around oncosphere
• embryophore +oncosphere 


  = cysticercus
• cysticerci is infective up to 10 weeks, remain viable for several months
• beef tapeworm


  rare in India as Hindus don't eat beef
• pork tapeworm 


  rare in Muslim countries as don't eat pork
• symptoms in humans

  • intestinal blockage
  • psychological distress
  • digestive disturbance
  • abdominal pain
  • weight loss
  • nausea
• Taeniasis can be treated with

  praziquantel
• cysticercosis is caused by Taenia solium (pork) where human is intermediate host by accident by 


  eating contaminated vegetation (with eggs of tapeworm)
• cysticercosis caused by faecal oral route
• symptoms occur


  months to years after infection
• praziquantel kills viable cysts, provoke inflammatory response, make symptoms worse, co-administration with corticosteroids to manage inflammation
• dog tapeworm 


  dog is definitive host, humans can become intermediate host
• diagnosis of dog tapeworm

  • ultrasound
  • only discovered in autopsy
• treatment of echinococcosis

  • PAIR- puncture, aspiration, injection and re-aspiration
  • surgery if lesions are confined
  • drug treatment -albendazole
  • watch and wait