Intro to Cestodes

Cards (14)

  • Phylum Platyhelminthes (Flatworms)
    • Multicellular animals characterized by a flat, bilaterally symmetric body
    • Dorsoventrally flattened and solid (no body cavity)
    • Hermaphroditic, having both male and female reproductive organs in the same individual
    • Overall size varies greatly, some members are as small as 1 mm, and others may be 20 meters or longer
    • The classes Cestoda (tapeworms) and Trematoda (flukes) contain species parasitic to humans
  • Cestodes
    • Flat, segmented body with various length (several mm – several meters)
    • Hermaphroditic with each proglottid developing both male and female reproductive organs, and mature eggs developing in the most distal proglottids
    • No circulatory system
    • No digestive system
    • Microtriches – outward projections present in the tegument, similar to microvilli of our gut mucosal cells, increase the surface area for nutrient absorption, interdigitate with host microvilli
  • Cestodes are diagnosed by
    Finding eggs or proglottids (diagnostic stage) in the feces
  • Habitat of adult tapeworm
    Intestine of the definitive host
  • Intermediate host
    Larval stage encysted in the tissue
  • Mnemonics for Taenia species
    • Adult worms are seen in the intestine
    • Proglottids contain male and female parts
    • Eggs have 6 hooked embryos
    • World-wide distribution
    • No respiratory, vascular, or digestive system
    • Ribbon-like body, flat
    • Middle (intermediate host is required)
  • Cestode structure
    • Scolex (head)
    • Neck (germinal portion)
    • Strobila (immature, mature, gravid proglottids/segments)
  • Scolex
    • Similar to the head, knobby-looking and has either suckers or sucking groove for attachment to the mucosa
    • Rostellum: armed with hooks for attachment to the intestinal wall, particularly important during digestion
    • Suckers for the absorption of nutrients once the hooklets have penetrated the intestinal wall
  • Neck
    Germinal portion that produces new proglottids, the segment of proglottids become mature as they move away from the scolex or the neck portion
  • Strobila
    Immature, mature, gravid proglottids (segments) that bud from behind the scolex, mature and fill with eggs, and become gravid proglottids
  • Anatomy of proglottids
    • Immature: reproductive organs are undifferentiated
    • Mature: reproductive organs are differentiated (kidney-shaped ovaries, surrounding testes)
    • Gravid: uterus with lateral branches filled with eggs, reproductive organs start to disintegrate
  • Classification of Cestodes
    • Species which require a vertebrate intermediate host (Taenia solium, Taenia saginata, Echinococcus granulosus)
    • Species which require an invertebrate intermediate host (Dipylidium caninum, Hymenolepis diminuta, Raillietina garrisoni)
    • Species which may or may not require intermediate host (Hymenolepis nana)
    • Species which infect man in their larval stages (Echinococcus granulosus, Echinococcus multilocularis, Taenia solium, Diphyllobothrium latum)
  • Binomial names and common names of Cestodes
    • Taenia saginata (Beef tapeworm)
    • Taenia solium (Pork tapeworm)
    • Taenia multiceps (Coenurus tapeworm)
    • Echinococcus granulosus (Hydatid tapeworm)
    • Echinococcus multilocularis (The multiloculate or Alveolar Hydatid tapeworm)
    • Hymenolepis nana (Dwarf tapeworm)
    • Hymenolepis diminuta (Rat tapeworm)
    • Dipylidium caninum (Double-pored tapeworm)
    • Diphyllobothrium latum (Broad Fish tapeworm)
  • Comparison of Pseudophyllidean and Cyclophyllidean Cestodes
    • Scolex: Pseudophyllidean - Almond/Spatulate, 2 slit-like grooves (bothria); Cyclophyllidean - Globular, 4 cup-like suckers
    • Uterus: Pseudophyllidean - No branching, with pores; Cyclophyllidean - Branching, blind sac
    • Uterine pore: Pseudophyllidean - Present; Cyclophyllidean - Absent
    • Genital pore: Pseudophyllidean - Ventral, in the midline; Cyclophyllidean - Lateral
    • Eggs: Pseudophyllidean - Operculated, gives rise to ciliated larvae; Cyclophyllidean - Not operculated, do not give rise to ciliated larvae
    • Intermediate host: Pseudophyllidean - 2; Cyclophyllidean - 1 or none
    • Apolysis: Pseudophyllidean - Anapolytic (proglottids are not shed off because they have uterine pore); Cyclophyllidean - Apolytic (proglottids are shed off because they do not have uterine pore)