CESTODES

• Cestodes (Tapeworm)


  • Phylum: Platyhelminthes
  • Class: Cestoda
• Intestinal species


  • Dipylidium caninum
  • Diphyllobothrium latum
  • Hymenolepis diminuta
  • Hymenolepis nana
  • Taenia saginata
  • Taenia solium
  • Taenia asiatica
• Extraintestinal species


  • Echinoccocus granulosus
  • Spirometra species
• General Characteristics


  • Dorsoventrally flattened
  • Bilateral symmetry
  • Segmented with ribbon-like appearance
  • No digestive tract
  • Hermaphroditic
• Order


  • Pseudophyllidea
  • Cyclophyllidea
  • Hymenolepididae
  • Dipylidiidae
• Family


  • Diphyllobothriidae
  • Taeniidae
  • Hymenolepididae
  • Dipylidiidae
• Genus


  • Diphyllobothrium, Spirometra
  • Taenia, Echinococcus
  • Hymenolepis
  • Dipylidium
• Dipylidium caninum (Dog or cat tapeworm, Pumpkin seed tapeworm)


  Dipylidiasis in humans is accidental
• Dipylidium caninum parasite biology

  • Scolex: small, globular with 4 deeply cupped suckers; protrusible rostellum, armed with one to seven rows of rose-thorn shaped hooklets
  • Proglottids: narrow, two sets of male and female reproductive organs and bilateral genital pores
  • Gravid Proglottids: pumpkin seed shape and size; filled with capsules or packets of about 8-15 eggs enclosed in an embryonic membrane
• Dipylidium caninum ova


  • Released by contraction of the proglottids or by its disintegration out of the host
  • Eggs: spherical, thin-shelled with a hexacanth embryo
• Dipylidium caninum intermediate hosts

  • Ctenocephalides canis
  • Ctenocephalides felis
  • Pulex irritans
  • Trichodectes canis
• Dipylidium caninum pathogenesis and clinical manifestations


  • Infection rarely heavy
  • Symptoms minimal
  • Slight intestinal discomfort, epigastric pain, diarrhea, anal pruritus, allergic reactions
  • Most patients are asymptomatic
  • Moderate eosinophilia reported
• Dipylidium caninum diagnosis


  • Recovery of characteristic gravid proglottids passed out singly or in chain
  • Proglottids should be pressed or flattened between two glass slides
  • Not recommended: stool examination for presence of egg capsules
• Diphyllobothrium latum (Broad fish tapeworm)

  • Size: 4-10m in length
  • Scolex: spatulate, 2 bothria/sucking grooves
  • Egg: yellowish brown, thick shell, inconspicuous operculum, opposite operculum is a small knob like opening, unembryonated
  • Mature proglottids: broader than they are long; uterus: coiled in "rosette appearance"; genital pore: center of the proglottid
• Diphyllobothrium latum life cycle

  • 1st intermediate host: copepods (cyclops/diaptomus)
  • 2nd intermediate host: freshwater fish
  • Infective stage: plerocercoid larva
• Diphyllobothrium latum diagnostic stage

  Eggs, proglottid
• Diphyllobothrium latum pathogenesis


  • Hyperchromic, megaloblastic anemia with thrombocytopenia and leukopenia
  • Competes with vitamin B12 for humans
  • Vitamin B12 content of D. latum is approximately 50 times that of T. saginata
• Diphyllobothrium latum diagnosis


  • Residence in or travel to an endemic area, a raw-fish diet, and a pernicious type of anemia: suggestive of Diphyllobothriasis
  • Definite diagnosis: operculated eggs, proglottids in stools
  • To differentiate anemia d/t diphyllobothriasis from pernicious anemia, Examination of gastric juice for presence of free hydrochloric acid is useful
• Hymenolepis diminuta (Rat tapeworm)

  • Habitat: small intestine
  • Scolex: unarmed rostellum
  • Strobila: unilateral genital pores, same as H. nana
  • Eggs: circular, bile stained, fan like arrangement of hooks, presence of bipolar thickenings but without filaments, "sunny side/fried egg appearance"
  • Infective stage: cysticercoid larva
  • Intermediate host: insects (rat flea, flour beetle, cockroach)
  • Final host: rat
• Hymenolepis diminuta diagnosis


  • Identification of eggs from the stool
  • At times, whole worm is expelled and scolex morphology may be used to aid in diagnosis
• Hymenolepis nana (Dwarf tapeworm)

  • Size: Adult: 10-45mm (length), 0.1-1mm (width)
  • Habitat: small intestine
  • Eggs: with bipolar thickenings and polar filaments; spherical or subspherical, colorless, clay-colored, 30 to 47 um in diameter
  • Scolex: retractable rostellum with 29-30 Y shaped hooklets
  • Strobila: 175-220 segments; 3 testes 1 ovary
  • Oncosphere has thin membrane and thick membrane with conspicuous bipolar thickenings, from which arise 4-8 hair-like polar filaments embedded in the inner membrane
• Hymenolepis nana pathogenesis and clinical manifestations

  • Light worm burden: asymptomatic
  • Headache, dizziness, anorexia, pruritus of nose and anus, diarrhea, vomiting, abdominal pain, pallor, weight loss
  • Heavy infections –> enteritis due to necrosis and desquamation of the intestinal epithelial cells
• Hymenolepis nana diagnosis


  • Demonstartion of characteristic eggs in the patient's stool
  • Proglottids are not recovered (undergo degeneration prior to passage with stools)
• Hymenolepis nana criteria for cure

  Negative for eggs at stool for 1 month post treatment
• Taenia saginata (Beef tapeworm)

  • Adults measure 4-10m in length
  • May have 1,000 to 4,000 proglottids
  • Scolex: cuboidal (1-2 mm in diameter) with 4 acetabula, devoid of hooklets, no rostellum
  • Egg: hexacanth; sunburst appearance
  • Strobila/proglottids (gravid): 15 to 20 lateral branches (dichotomous/tree like); 97,000-124,000 ova; annually, a worm may pass out 594,000,000 ova
• Taenia saginata mature proglottids


  • Approximately square in shape
  • Contain mature female and male reproductive organs
  • 2 large lobes of ovaries and a median club shaped uterus
  • Follicular testes (300-400) are scattered throughout the proglottid
  • Vagina has a sphincter
• Taenia saginata gravid proglottids


  • Longer than they are wide (16-20mm by 5-7mm)
  • Most distal form of the neck
  • Uterus is distended with ova
  • 15-20 lateral branches
  • Genital pores are irregularly alternate
  • Undergo Apolysis
  • Either passed out with the feces or actively crawl out of the bowel to the external environment
• Taenia saginata infective stage and diagnostic stage


  • Infective stage: cysticercus bovis
  • Diagnostic stage: eggs, proglottids, scolex
• Taenia saginata pathogenesis


  • Epigastric pain, vague discomfort, hunger pangs, weakness, weight loss, loss of appetite, pruritus ani
  • Obstruction in appendix, bile and pancreatic ducts
• Taenia saginata diagnosis


  • Proglottids, eggs, or scolex
  • Gravid proglottids are pressed or flattened between two glass slides and examined against the light
  • Injection of India ink through the genital pore –> help one makes an accurate count of the lateral branches of the uterus
  • Mature segments can be stained to demonstrate VAGINAL SPHINCTER
  • Concentration techniques (formalin-ether/ethyl acetate conc)
  • Perianal swabs (eggs are left in the perianal skin as the gravid segments squeeze out of the anal opening
• Taenia saginata criteria for cure

  • Recovery of scolex
  • Negative stool examinations for 3 months
• Taenia solium (Pork tapeworm)

  • Shorter compared to T. saginata
  • Measure 2 to 4 m in length
  • May have 8,000-10,000 proglottids
  • Scolex: 4 acetabulum, smaller, more spherical than T. saginata; has cushion shaped rostellum with 25-30 hooklets
  • Egg: hexacanth, sunburst appearance
  • Female adult: no vaginal sphincter
  • Follicular testes: 100-200
  • Strobila/proglottids (gravid): undergo apolysis to release eggs; 7-13/7-15 lateral branches (dendritic/finger like); 30,000-50,000 ova; presence of ovarian lobe
  • Infective stage: cysticercus cellulosae
  • Diagnostic stage: eggs, proglottids, scolex
• Taenia solium pathogenesis (intestinal infection)

  • Mild, non-specific abdominal complaints
  • Obstruction of bile and pancreatic ducts
• Concentration techniques


  Formalin-ether/ethyl acetate concentration
• Perianal swabs


  Eggs are left in the perianal skin as the gravid segments squeeze out of the anal opening
• Taenia solium (Pork tapeworm)

  • Shorter compared to T. saginata
  • Measure 2 to 4 m in length
  • May have 8,000-10,000 proglottids
  • Scolex: 4 acetabulum, smaller, more spherical than T. saginata; has cushion shaped rostellum with 25-30 hooklets
  • Egg: hexacanth, sunburst appearance
  • Female adult: no vaginal sphincter
  • Follicular testes: 100-200
  • Strobila/proglottids (gravid): undergo apolysis to release eggs; 7-13/7-15 lateral branches (dendritic/finger like); 30,000-50,000 ova; presence of ovarian lobe
  • Infective stage: cysticercus cellulosae
  • Diagnostic stage: eggs, proglottids, scolex
• Intestinal infection


  Mild, non-specific abdominal complaints
• Intestinal infection


  Obstruction of bile duct, pancreatic duct, appendix is unlikely (proglottids not active)
• Cysticercosis


  • Most commonly located in striated muscle, brain but subcutaneous tissues, eye, heart, lung, and peritoneum may be involved
  • Upon death, cystic fluid increases, pronounced tissue response to parasite which is eventually calcified
• Neurocysticercosis (NCC)


  • Cysticerci containing a scolex – brain parenchyma/ floating freely in the ventricles
  • May also appear as large vesicular structures devoid of scolex; located in basal cisternal spaces