Intestinal Cestodes

• Intestinal Cestodes


  • Taenia saginata
  • Taenia solium
  • Hymenolepis nana
  • Hymenolepis diminuta
  • Raillietina garrisoni
  • Dipylidium caninum
  • Diphyllobothrium latum
• Platyhelminthes


  Phylum composed of 2 parasitic classes: Trematoda (flukes) and Cestoda (tapeworms)

  
• Cestoda


  • Pseudophyllidea (false tapeworm)
  • Cyclophyllidea (true tapeworm)

  
• Cestodes


  • Long, flat, ribbon-like appearance
  • 3 distinct features: Rostellum, Scolex, Proglottids

  
• Rostellum


  May have hooks/hooklets, crown of the scolex

  
• Scolex


  Head, contains suckers for intestinal attachment
• Proglottids


  Segments of cestodes, formed via budding, strobila: chain of proglottids, anterior: immature, middle: mature, near posterior: gravid, equipped with both male and female organs, hermaphroditic, gravid: filled with eggs

  
• Cysticercoid


  Larval stages found in tissues of intermediate host, infective stage of cestodes

  
• Egg (Cestodes)


  Consists of a hexacanth embryo (oncosphere) with six small hooks (hooklets)

  
• Taenia saginata


  Also known as "BEEF TAPEWORM", cosmopolitan, definitive host: humans, no human cysticercosis

  
• Taenia asiatica


  3rd species related to T. saginata, PCR used to differentiate, may be misidentified as T. saginata, cysticercus larvae found in liver of variable intermediate hosts, contains suckers but no rostellum, infective stage: Cysticercus bovis

  
• Taenia solium


  Also known as "PORK TAPEWORM", definitive & intermediate host: humans, causes more diseases compared to T. saginata, infective stage: Cysticercus cellulosae

  
• Differences between T. saginata and T. solium


  • Scolex: Cuboidal with 4 acetabula vs Spherical with 4 acetabula
  • Rostellum: Absent vs Present, cushion-like with double crown of 25-30 hooks
  • Number of segments: 1000-4000 & longer vs 8000-10,000 & wider
  • Action of segment: Actively crawling vs Not observed
  • Number of eggs: 97k-124k per proglottid vs 30k-50k per proglottid
  • Length: 4-10m vs 2-4m

  
• Eggs


  Infective stage of cysticercosis, subspherical, 30-45um, passed from feces, resistant when ingested, contain oncosphere with 3 pairs of hooklets, brownish and striated radially, embryo surrounded by embryopore

  
• Definitive Host


  Humans, ingestion of improperly cooked meat, larva digested out of meat, scolex evaginates to attach to small intestine mucosa
• Intermediate Host


  Cattle: T. saginata, oncosphere penetrates intestinal mucosa, enters venule, develops into Cysticercus bovis

  Pigs: T. solium

  Humans: T. solium
• Taeniasis


  Intestinal infection, nonspecific symptoms: epigastric pain, discomfort, hunger pangs, weakness, weight loss, loss of appetite, pruritus

  T. saginata: obstruction of bile, pancreatic ducts and appendix

  T. solium: no obstruction
• Cysticercosis


  T. solium, cysticerci often multiple and may occur in any organ/tissue, neurocysticercosis: most serious manifestation, neurologic deficits, obstructive hydrocephalus, convulsions, focal/generalized seizures
• Diagnosis


  Identification of proglottids, stain with india ink, serological tests, CSF, CT and MRI scans
• Treatment


  Taeniasis: Praziquantel, Praziquantel + Niclosamide

  Cysticercosis: Praziquantel, Albendazole
• Prevention & Control


  • Thorough cooking

  Freezing -20 degree Celsius for 10 days

  Sanitary inspection of livestocks

  Meat inspections
• Hymenolepis nana


  • Also known as "DWARF TAPEWORM", smallest tapeworm infecting humans, intermediate host may not be needed, adult resides in ileum, eggs hatch in duodenum (autoinfection), infective stage: cysticerci/embryonated egg

  
• Hymenolepis diminuta


  • Also known as "RAT TAPEWORM", accidental parasite of humans, larger than H. nana, requires intermediate host, infective stage: cysticerci/embryonated egg

  
• Differences between H. nana and H. diminuta


  • Scolex: Subglobular with 4 cup-shaped suckers vs Rudimentary

  Rostellum: Retractable 20-30 Y-shaped hooklets vs Absent

  Number of segments: Shorter vs Broader

  Length: 25-45mm vs 60cm
• H. nana Eggs


  Spherical/subspherical, colorless/clay-colored, 30-47um, oncosphere: thin outer & thick outer membrane with conspicuous bipolar thickenings with 4-8 hair-like polar filaments, die once passed out into environment
• H. diminuta Eggs


  Circular & are bile-stained, 60-80um, oncosphere: bipolar thickenings without filaments, fan-like hooklets
• H. nana Hosts


  Definitive Hosts: rats and humans, Intermediate Host: flour beetles (Tenebrio spp.)

  
• H. diminuta Hosts


  Definitive Host: rats, Accidental Host: humans
• H. nana Life Cycle


  Direct cycle: Host ingests eggs, hatches in duodenum, liberated/free embryos penetrate mucosal villi, develop to infective cysticercoid larvae, larvae break out of villi and attach to intestinal mucosa to become adults

  Indirect cycle: Via accidental ingestion of infected intermediate host

  
• H. nana: It takes 20-30 days from time of ingestion for eggs to appear in feces
• H. diminuta: Larva released takes about 3 weeks to become an adult
• H. nana Disease


  Intestinal infection, nonspecific symptoms
• H. diminuta Disease


  Accidental parasite of humans

  
• H. diminuta


  • Circular & are bile-stained
  • 60-80um
  • Oncosphere: Bipolar thickenings without filaments
  • Fan-like hooklets
• Hosts


  • H. nana: Definitive Hosts - rats and humans, Intermediate Host - flour beetles (Tenebrio spp.)
  • H. diminuta: Definitive Host - rats, Accidental Host - humans

  
• Life Cycle


  1. Direct cycle: Host ingests eggs and hatches in duodenum, liberated/free embryos penetrate mucosal villi where they develop to infective cysticercoid larvae, After 4-5 days, larvae breaks out of villi and attach to intestinal mucosa where they become adults

  2. Indirect cycle: Via accidental ingestion of infected intermediate host

  
• Hymenolepiasis


  Self-limiting due to immunity
• H. nana


  • Light worm burden (asymptomatic)
  • Heavy infections results in: Enteritis, Desquamation of intestinal epithelial cells
  • In children: Restless, Irritable, Sleep disturbances

  
• Clinical Manifestation of H. nana


  • Headache
  • Dizziness
  • Anorexia
  • Pruritus of nose and anus
  • Diarrhea
  • Vomiting
  • Abdominal pain
  • Pallor
  • Weight loss
  • Convulsions (rare)
• H. diminuta


  • Highest number recorded: 19 worms
  • Minimal and non-specific
  • Human infections usually light