para-cestodes

• Phylum Platyhelminthes


  Collectively called the flatworms
• Phylum Platyhelminthes


  • Dorsoventrally flattened
  • Bilaterally symmetrical
  • Covered by a membrane called tegument
  • Hermaphrodite except for Schistosoma species

  
• Differences between Cestodes and Trematodes

  • Cestodes: Segmented, ribbon-like appearance
  • Trematodes: Unsegmented, leaf-like appearance
  • Cestodes: No digestive tract, no circulatory system
  • Trematodes: Incomplete digestive tract
  • Cestodes: Mostly hermaphroditic
  • Trematodes: Hermaphroditic
  • Cestodes: Mostly found in the intestines
  • Trematodes: Found in blood, liver, lung, intestines
  • Cestodes: Some require 2 intermediate hosts
  • Trematodes: Require 2 intermediate hosts

  
• Class Cestoda


  • Adult worms are seen in the intestine
  • Proglottids contain male and female parts
  • Eggs have 6 hooked embryos
  • World-wide distribution
  • No digestive tract, no circulatory system
  • Ribbon-like body, flat
  • Middle (intermediate host is required)
• Orders of Class Cestoda

  • Pseudophyllidea
  • Cyclophyllidea
• Pseudophyllidea tapeworms


  • Diphyllobothrium latum
  • Spirometra: S. erinacei, S. mansoni, S. ranarum

  
• Cyclophyllidea tapeworms


  • Taenia solium and Taenia saginata
  • Hymenolepis nana and Hymenolepis diminuta
  • Dipylidium caninum
  • Raillietina garrisoni
  • Echinococcus granulosus

  
• Differences between Pseudophyllidea and Cyclophyllidea

  • Scolex: Pseudophyllidea - Spatulate with sucking grooves, Cyclophyllidea - Globular with 4 muscular suckers
  • Pores: Pseudophyllidea - Genital + Uterine pores, Cyclophyllidea - Genital pores
  • Eggs: Pseudophyllidea - Operculated and immature, require aquatic development, Cyclophyllidea - Non-operculated and readily passed out containing hexacanth embryo
  • Intermediate Hosts: Pseudophyllidea - Require 2 IHs, Cyclophyllidea - Require only 1 IH
  • Mode of Transmission: Pseudophyllidea - Consumption of infected intermediate host, Cyclophyllidea - Consumption of infected host, also infection via consumption of larval and cystic stages
• Medically important tapeworms


  • Taenia saginata (Beef Tapeworm)
  • Taenia solium (Pork Tapeworm)
  • Taenia multiceps (Coenurus Tapeworm)
  • Echinococcus granulosus (Hydatid Tapeworm)
  • Echinococcus multilocularis (Multiloculate or Alveolar Hydatid Tapeworm)
  • Hymenolepis nana (Dwarf Tapeworm)
  • Hymenolepis diminuta (Rat Tapeworm)
  • Dipylidium caninum (Double-pored Tapeworm)
  • Diphyllobothrium latum (Broad Fish Tapeworm)

  
• Types of proglottids


  • Immature - Undeveloped sexual organ, nearest to the neck
  • Mature - Fully mature sexual organ
  • Gravid - Contains fertilized egg, undergoes apolysis
• Pseudophyllidean tapeworms have a spatulated scolex with bothria, genital pores and uterine pores, and operculated immature eggs that require aquatic vegetation to develop

  
• Cyclophyllidean tapeworms have a globular scolex with 4 muscular suckers, no uterine pore but undergo apolysis, and non-operculated eggs with hexacanth embryos that are readily passed out

  
• Larval stages of tapeworms

  • Pseudophyllidea: Procercoid in 1st IH, Plerocercoid in 2nd IH
  • Taenia: Cysticercus
  • Hymenolepis, Dipylidium, Raillietina: Cysticercoid
  • Echinococcus: Hydatid cyst

  
• Tapeworm species requiring vertebrate intermediate hosts

  • Taenia solium (pork tapeworm)
  • Taenia saginata (beef tapeworm)
  • Echinococcus granulosus (dogs, carnivores)

  
• Tapeworm species requiring invertebrate intermediate hosts

  • Dipylidium caninum (dog tapeworm, double-pored tapeworm)
  • Hymenolepis diminuta (rat tapeworm)
  • Raillietina garrisoni (Tribolium confusum)

  
• Hymenolepis nana (dwarf tapeworm) may or may not require an intermediate host
• Tapeworm species that infect humans in their larval stages

  • Echinococcus granulosus (hydatid worm)
  • Echinococcus multilocularis
  • Taenia solium
  • Diphyllobothrium latum

  
• Diphyllobothrium latum


  • Scolex is spoon-shaped or spatulate with 2 slit-like grooves called bothria
  • Scolex has no rostellum and no hooklets
  • Neck is thin and unsegmented, much longer than the head
  • 3,000 to 4,000 proglottids
  • Mature segment is filled with male and female reproductive organs
  • Terminal segments shrink and become empty as eggs are discharged
  • Uterus appears as a rosette in the center of the segment

  
• Diphyllobothrium latum eggs


  66 x 44 μm, oval, bile stained, contain abundant granules and unsegmented ovum, have inconspicuous operculum and small knob, do not float in saturated salt solutions, give rise to a single larva, about 1 million released everyday
• Larval stages of Diphyllobothrium latum

  • Coracidium (first stage larva - ciliated oncosphere that develops from egg in water)
  • Procercoid (second stage larva - spindle-like solid body with cephalic invagination, found in cyclops)
  • Plerocercoid (third stage larva - head invaginated in neck, found in freshwater fish)

  
• Hosts of Diphyllobothrium latum

  • Definitive host: Man, dog, cat (small intestine)
  • First intermediate host: Cyclops or Diaptomus
  • Second intermediate host: Freshwater fish (pike, trout, salmon, perch)
• Diagnosis of Diphyllobothrium latum

  Microscopic examination of feces for characteristic operculated eggs
• Differences between Taenia solium and Taenia saginata

  • Length: T. solium 3-5m, T. saginata 5-10m
  • Number of segments: T. solium 800-1000, T. saginata 1000-2000
  • Scolex: T. solium globular with 4 suckers and rostellum with hooks, T. saginata globular with 4 suckers without rostellum
  • Mature proglottids: T. solium has accessory ovary, T. saginata does not
  • Gravid proglottids: T. solium 8-12 lateral branches, T. saginata 15-30 lateral branches
  • Apolysis: T. solium in chains, T. saginata singly
  • Eggs per gravid proglottid: T. solium 30,000-50,000, T. saginata 80,000
  • Egg size: T. solium 31-56 μm, T. saginata similar
  • Intermediate host: T. solium - pig, T. saginata - cow
  • Infective larval stage: T. solium - cysticercus cellulosae, T. saginata - cysticercus bovis
• Diagnosis of Taenia solium and Taenia saginata

  • Taeniasis: Anal swab to find eggs, fecal exam to find segments

  Cysticercosis (T. solium): Biopsy of subcutaneous nodule, X-ray/CT/MRI for cerebral cysticercosis, ophthalmoscopy for ophthalmic cysticercosis
• Hymenolepis nana and Hymenolepis diminuta

  • Hymenolepis nana - Dwarf tapeworm

  Hymenolepis diminuta - Rat tapeworm

  
• Rostellum


  and hooklets
• Diagnosis of Cysticercosis


  • Biopsy (subcutaneous nodule)
  • X-ray/CT/MRI: cerebral cysticercosis
  • Ophthalmoscopy: ophthalmic cysticercosis
• Diagnosis of Taeniasis


  • Anal swab: to find egg at perianal region
  • Fecal exam: to find segment (species identification)

  
• Arthropod Intermediate Hosts


  • Rat flea - Xenopsylla spp.
  • Dog flea - Ctenophalides canis
  • Human flea - Pulex irritans
  • Flour beetle - Tribolium spp.
• Diagnosis of Hymenolepis nana

  • Demonstration of eggs in stool
  • Light infection: concentration of stool on alternate days
  • Stool exam repeated after 2 weeks
• Proglottids are not recovered - undergo degeneration prior to passage with stools
• At times whole worm is expelled
• Intermediate Hosts of Dipylidium caninum

  • Ctenocephalides canis (dog flea)
  • Ctenocephalides felis (cat flea)
  • Trichoedectes canis (dog louse)
  • Pulex irritans (human flea)
• Intermediate Host of Raillietina garrisoni

  • Tribolium confusum (flour beetle)
• Diagnosis of Dipylidium caninum and Raillietina garrisoni

  • recovery of gravid segments
  • egg capsules are rarely passed-out in the feces (Dipylidium caninum)
  • segment is glistening with rice grain appearance (Raillietina garrisoni)
• Extra Intestinal Cestodes


  • Echinococcus granulosus
  • Echinococcus multilocularis
  • Spirometra mansoni
  • Spirometra erinacei
  • Spirometra ranarum
• Echinococcus granulosus Scolex


  bears a prominent rostellum with double row of 20 to 40 large and small hooklets

  
• Echinococcus granulosus Segments


  3 segments: 1 immature, 1 elongated mature, 1 long gravid

  
• Echinococcus granulosus Ova


  subspherical with a brown radially striated embryophore which cannot be differentiated from Taenia eggs

  
• Echinococcus granulosus Hydatid cyst

  infective stage of the parasite, 20 cm in diameter, developing membrane is 2 layers: outer laminated layer (milky opaque, non-nucleated) and inner nucleated germinal layer, buds or capsules which contain protoscolices