Cestodes

• Cestodes


  Also known as the tapeworms, they are flatty helminths because they are flat
• Cestodes


  • Flat dorsoventrally, meaning flat in front and back
• Parts/Regions of adult tapeworm

  • Scolex
  • Neck
  • Strobila

  
• Scolex


  • Head (of the cestodes) for attachment, with accessory structures like sucking grooves, cup-like suckers, rostellum, and hooklets
• Neck


  • Region of growth, produces immature segments
• Strobila


  • Chain of proglottids or segments
• Types of segments


  • Immature segment
  • Mature segment
  • Gravid (ripe) segment
• Larval stages (solid type)

  • Plerocercus/Procercoid/Procercus (in 1st intermediate host, immature/non-infective)
  • Plerocercoid/Sparganum larva (in 2nd intermediate host, mature/infective)

  
• Larval stages (cystic type)

  • Cysticercoid (with slightly developed bladder)
  • Cysticercus (true bladder worm, head navigated into bladder)

  
• Order Pseudophillidea


  • Scolex typically unarmed, with a dorsal and ventral groove (bothria)
• Order Cyclophillidea


  • Scolex with 4 suckers and usually a centrally placed apical rostellum, frequently armed with hooks
• Bases for differentiation between Pseudophillidea and Cyclophillidea


  • Shape of scolex
  • Accessory organ in scolex
  • Appearance of uterus
  • Eggs/ova
  • Embryo
  • Larval stage
  • Ways of releasing eggs in gravid segment
  • Number of intermediate hosts utilized

  
• Medically important species of tapeworms

  • Diphylluobothrium latum (Order Pseudophillidea)
  • Taenia solium (Order Cyclophillidea, vertebrate IH)
  • Taenia saginata (Order Cyclophillidea, vertebrate IH)
  • Dipylidium caninum (Order Cyclophillidea, invertebrate IH)
  • Hymenolepis diminuta (Order Cyclophillidea, invertebrate IH)
  • Raillietina garisoni (Order Cyclophillidea, invertebrate IH)
  • Hymenolepis nana (Order Cyclophillidea, no IH)
  • Echinococcus granulosus (Order Cyclophillidea, larval stage infects man)
  • Echinococcus multiocularis (Order Cyclophillidea, larval stage infects man)
  • Taenia solium (Order Cyclophillidea, larval stage infects man)
  • Spirometra mansoni (Order Cyclophillidea, larval stage infects man)

  
• Adult tapeworm


  • Long, tape-like multi-segmented worms flattened dorsoventrally
  • Found in the small intestine of man
  • No circulatory system and is usually divided into segments or proglottids
  • No digestive system
  • Nervous system is confined primarily in the scolex
  • Excretory system consists of flame cells, capillaries and collecting tubules
  • Reproductive system consists of both male and female which are both present in each segment (monoecious)

  
• Three parts/regions of adult tapeworm

  • Scolex
  • Neck
  • Strobila

  
• Scolex


  • Head
  • For attachment (holdfast organ)
  • Accessory structures present that will help in the attachment
  • 2 sucking grooves/sulci
  • 4 cup-like suckers (in some species)
  • Rostellum
  • Hooklets
• Neck


  • Region of growth
• Strobila


  • Chain of proglottids or segments
• Three types of segments

  • Immature segment
  • Mature segment
  • Gravid segment
• Immature segment


  Present near the neck. The male and female sex organs are still immature and are not differentiated
• Mature segment


  • Large segment. Male and female sex organs are differentiated
  • Each segment contains single, sometime two sets of male and female genital organs
• Gravid segment


  • Situated farthest away from the scolex
  • Uterus is completely filled up with eggs
• Larval stages


  • Solid type
  • Cystic type
• Plerocercus/Procercoid/Procercus


  • Present in the 1st IH
  • Relatively globular with the scolex invaginated into the body
• Plerocercoid/Sparganum larva


  • Present in the 2nd IH
  • Elongated with head free or invaginated only in the neck

  
• Cysticercoid


  • Larva is provided with a slightly developed bladder anteriorly, into which the head is invaginated and with an elongated solid posterior portion
• Cysticercus (true bladder worm)


  • In this type of larva, head is invaginated into the proximal portion of the bladder
  • Simple, Coenurus, Echinococcus/Hydatid

  
• Order Pseudophillidea


  • Scolex typically unarmed, with a dorsal and ventral grooves (bothria)
  • All representatives in man belong to Superfamily Bothriocephaloidea
• Order Cyclophillidea


  • Scolex with 4 suckers and usually a centrally placed apical rostellum, frequently armed with hooks
  • All species found in man belong to Superfamily Taeniodea
• Medically important species of tapeworms

  • Diphyllobothrium latum
  • Taenia solium
  • Taenia saginata
  • Dipylidium caninum
  • Hymenolepis diminuta
  • Raillietina garisoni
  • Hymenolepis nana
  • Echinococcus granulosus
  • Echinococcus multilocularis
  • Spirometra mansoni

  
• Apolysis


  Detachment of gravid segment
• Pseudophyllidean tapeworms have a ciliated embryo

  
• Cyclophyllidean tapeworms have a 3 pairs of hooklets on the embryo

  
• Intermediate hosts for cyclophyllidean tapeworms

  • Insects
  • Mites
  • Ticks

  
• Intermediate hosts for pseudophyllidean tapeworms

  • Crustaceans
  • Fish

  
• Procercoid and plerocercoid are both infective stages to humans
• Diphyllobothrium latum


  • Formerly known as Dibothriocephalus latus
  • Longest tapeworm of man measuring 3-10 meters or more
  • A single worm may discharge as many as 1 million eggs/day

  
• Scolex of D. latum

  • Elongated, and spoon-shaped, spatulate or almond-shaped with 2 dorsoventral sucking grooves or bothria
  • It lacks suckers and hooks
• Neck of D. latum


  • Thin, unsegmented and is relatively much longer than head
• Strobila of D. latum

  • Consists of 3000-4000 segments
  • The mature and gravid segments are broader than long
  • Each mature segment contains a bilobed ovary present near the rear end of the segment, a central rosette uterus, and three genital openings (vas deferens, vagina, uterus) situated close to each other