Cestodes

• Cestodes


  Long, segmented, flattened dorsoventrally/tape-like worms/ ribbon-like hence also called as tapeworms

  
• Cestodes


  • Segmented unlike trematodes which are nonsegmented, flat, and leaflike
  • Monoecious/Hermaphroditic
  • No gastrointestinal tract/alimentary canal (no mouth, no anus)
  • Entry of nutrients and exit of waste: Integument
  • No circulatory system
  • With well-developed reproductive organs: testes, ovary, uterus
  • Mode of Transmission: Oral Route
  • Habitat: Small Intestine

  
• Life Span


  • Up to 25 years: D. latum, T. saginata, and T. solium
  • Usually <1 year: D. caninim and H. diminuta
  • Perhaps many years as a result of autoinfection: H. nana
• Treatment


  • Generally Praziquantel
  • Cysticercosis and Hydatid Disease: Albendazole, Mebendazole
• Parts of the Cestode

  • Head or scolex: It is the organ of attachment
  • Neck: the portion from which the segments (proglottids) arise
  • Strobila is the body or trunk of the cestodes, which is surrounded by a body wall called a tegument
• Scolex


  • In Cyclophyllidean cestodes, the scolex bears four cup like muscular suckers (or acetabula). In some species like T. solium and H. nana, scolex has a beak-like apical protrusion called as rostellum, which may be armed with hooklets.
  • In Pseudophyllidean cestodes, the scolex doesn't possess suckers but it bears a pair of longitudinal grooves called as bothria by which it attaches to the small intestine.

  
• Proglottids


  • Immature segments: Male and female reproductive organs are not differentiated
  • Mature segments: Contain male and female organs in the same segment, male organ appear first
  • Gravid segments or fertilized segments: Following fertilization, the uterus gets filled with eggs. Other organs are atrophied.

  
• Pseudophyllidean cestodes: Eggs


  Ovoid, operculated, surrounded by a single layer called an egg shell (or capsule), inside which the embryo is present containing three pairs of hooklets. Membrane lining the embryo is ciliated. The eggs, when laid first in the feces, are not embryonated. Maturation takes place later in water.

  
• Cyclophyllidean cestodes: Eggs


  Round to oval, covered by two layers—an outer egg shell (or capsule) filled with yolk material (thin, so might be lost) and an inner thick radially striated embryophore surrounding the embryo. Eggs are embryonated from the beginning, containing six hooklets but the lining membrane is not ciliated.

  
• Pseudophyllidean cestodes: Larva


  • Coracidium: First stage larva of Diphyllobothrium
  • Procercoid: Second stage larva of Diphyllobothrium
  • Plerocercoid: Third stage larva of Diphyllobothrium
  • Sparganum: Larval stage of Spirometra

  
• Cyclophyllidean Cestodes: Larvae


  • Cysticercus: Larval stage of Taenia
  • Hydatid cyst: larval stage of Echinococcus
  • Coenurus: Larval stage of Multiceps
  • Cysticercoid: Larval stage of Hymenolepis.

  
• Differences between Pseudophyllidean and Cyclophyllidean Cestodes

  • Scolex: Spoon-shaped (spatula) or Almond with slit-like sucking grooves (Bothria) vs Globular/Pyriform Quadrate: with four cuplike suckers, With/Without Rostellum Armed: with hooks, Unarmed: without hooks
  • Strobila: Anapolytic (not shedding segments) vs Apolytic (shedding segments)
  • Ova: Oval, operculated, immature vs Spherical, non-operculated, embryonated (hexacanth embryo)
  • Larval Stages: Coracidium > Procercoid > Plerocercoid (Infective Stage) vs Cysticercus, Hydatid cyst, Coenurus, Cysticercoid, Sparganum
  • Intermediate Hosts: Two (Crustaceans (Copepods), Cyclops; Freshwater Fish) vs Species which require vertebrate IH: T. solium, T. saginata, Species which require invertebrate IH: D. caninum, Species which may or may not require IH: H.nana
  • Gravid Proglottid: All reproductive structures are seen, Uterus: Rosette-like appearance vs Uterus can only be seen, Uterus: in different shapes/patterns

  
• Diphyllobothrium latum


  • Common Name: Broad/Fish Tapeworm
  • Largest tapeworm of man
  • Scolex is spatulate/spoon-shaped/diamond-shaped with sucking organ called bothrium
  • Uterus with characteristic rosette formation (highly-coiled uterus) - Eggs are operculated, immature
  • Larval stages: coracidium > procercoid > plerocercoid
  • Habitat: Small Intestine
  • Final Host: Man
  • Reservoir Host: Dogs, cats, rats, and other fish-eating mammals
  • 1st Intermediate Host: Copepods (Cyclops)
  • 2nd Intermediate Host: Freshwater Fish (Small Fishes)
  • Paratenic Host: Carnivorous Fish (Bigger Fishes: usually eaten by man)
  • Infective Stage: Plerocercoid Larva
  • Diagnostic Stage: Egg/Scolex (complete/successful treatment);no segments seen (anapolytic)
  • Mode of Transmission: Ingestion of raw or undercooked fish with plerocercoid larvae
  • Adults: confused with Spirometra spp.
  • Eggs: confused with Paragonimus westermani
  • Pathology: Causes hyperchromic, megaloblastic anemia with thrombocytopenia and leukopenia; competes with Vitamin B12 for humans (content is about 50 times than T. saginata)

  
• Spirometra spp.


  • Medically important species: S. mansoni, S. theileri, S. erinacei
  • Can accidentally infect man and cause disease called as sparganosis (caused by sparganum: plerocercoid larva)
  • Definitive Host: Dogs, cats
  • First Intermediate Host: Copepods (Cyclops)
  • Second Intermediate Host: Snakes, frogs, fishes
  • Accidental Host: Man
  • Adults are mistaken for adult Diphyllobothrium latum
  • Modes of Transmission: Drinking water containing copepods infected with sparganum, Eating frogs, snakes infected with larvae, Applying larvae infected products from frogs or snakes into open sores/wounds

  
• Taenia saginata


  • Common Name: Beef Tapeworm
  • Longest tapeworm of man
  • Length: up to 25 meters
  • 15-20 lateral branches: Dichotomous/Tree-like
  • Scolex: cuboidal, with 4 acetabula; no hooklets and rostellum (unarmed)
  • Proglottid: Taller than wide
  • Habitat: Small Intestine
  • Final Host: Man
  • Intermediate Host: Cattles, Cows, Camels
  • Infective Stage: Cysticercus Bovis
  • Mode of Transmission: Ingestion of raw or undercooked beef
  • Eggs: Spherical, striated, embryonated eggs with oncosphere (indistinguishable with T.solium egg)
  • Acid fast
  • Laboratory: Stool Examination: Eggs and Proglottids; Perianal Swab, Double Slide Compression Technique – inject dye (India Ink) [count the uterine branches]
  • Pathology: Causes Taeniasis bovis: mild epigastric pain, obstruction in appendix, bile, and pancreatic ducts

  
• Taenia solium


  • Common Name: Pork Tapeworm
  • Length: shorter < 7 meters
  • 7-13 lateral branches: Dendritic/Finger-like
  • Proglottid: Wider than tall
  • Habitat: Small Intestine
  • Final Host: Man
  • Intermediate Host: Pig (Intestinal Taeniasis); Man (Cysticercosis)
  • Infective Stage: Cysticercus Cellulosae (Intestinal Taeniasis); Embryonated Eggs (Cysticercosis)
  • Mode of Transmission: Ingestion of measly pork (intestinal taeniasis) and embryonated eggs (cysticercosis)
  • Eggs: Spherical, striated, embryonated eggs with oncosphere (indistinguishable with T.saginata egg)
  • Laboratory: Stool Examination: Eggs and Proglottids; Perianal Swab Double Slide Compression Technique – inject dye (India Ink) [count the uterine branches]
  • Pathology: Causes Taeniasis Autoreinfection (external, internal) Cysticercosis

  
• Cysticercosis


  Any organ or tissue may be involved, the most common being subcutaneous tissues and muscles.
• Taenia solium


  Pork Tapeworm

  
• Taenia solium


  • Length: shorter < 7 meters
  • 7-13 lateral branches: Dendritic/Finger-like
  • Proglottid: Wider than tall
  • Habitat: Small Intestine
  • Final Host: Man
  • Intermediate Host: Pig (Intestinal Taeniasis); Man (Cysticercosis)
  • Infective Stage: Cysticercus Cellulosae (Intestinal Taeniasis); Embryonated Eggs (Cysticercosis)

  
• Mode of Transmission


  Ingestion of measly pork (intestinal taeniasis) and embryonated eggs (cysticercosis)

  
• Eggs


  Spherical, striated, embryonated eggs with oncosphere (indistinguishable with T.saginata egg)

  
• Laboratory


  Stool Examination: Eggs and Proglottids; Perianal Swab Double Slide

  
• Compression Technique


  Inject dye (India Ink) [count the uterine branches]
• Pathology


  Causes Taeniasis, Autoreinfection (external, internal), Cysticercosis
• Any organ or tissue may be involved, the most common being subcutaneous tissues and muscles
• Neurocysticercosis


  The most common and most serious form
• Ocular Cysticercosis


  Cysts are found in vitreous humor, subretinal space and conjunctiva
• Taenia spp. comparison


  • Taenia saginata (Beef tapeworm)
  • Taenia solium (Pork Tapeworm)
  • Taenia asiatica

  
• Taenia asiatica


  • 3rd Taenia spp.
  • Closely related to T. saginata
  • In contrast to T. saginata, the cysticercus larvae (IS: cysticercus viscerotropica) were found in the liver of various intermediate hosts that include pigs, cattles, goats, wild boards, and monkeys

  
• Hymenolepis nana


  Dwarf Tapeworm, Smallest tapeworm of man, Most common cestode of man, True human tapeworm

  
• Hymenolepis nana


  • Habitat: Small Intestine
  • Final Host: Man (Children)
  • Reservoir Hosts: Mice, Rats
  • Intermediate Host: Direct - Do not require IH; Ingestion of Embryonated Egg, Indirect - Require IH (Flea/Bettle)
  • Infective Stage: Direct - Embryonated Egg, Indirect - Cysticercoid Larvae
  • Mode of Transmission: Ingestion of embryonated egg (direct); Accidental ingestion of IH containing larva (indirect)

  
• Hymenolepis nana Eggs


  Contain an oncosphere with two polar thickenings from which arise 4-8 polar filaments

  
• Hymenolepis diminuta


  Rat Tapeworm

  
• Hymenolepis diminuta


  • Habitat: Small Intestine
  • Final Host: Rat
  • Accidental Host: Man
  • Intermediate Host: Rat Flea, Flour Beetle, Cockroach
  • Infective Stage: Cysticercoid Larvae
  • Mode of Transmission: Ingestion of IH

  
• Hymenolepis diminuta Eggs


  Contain an oncosphere with polar thickenings but without filaments; "sunny side up/fried egg appearance"

  
• Hymenolepis spp. comparison


  • Hymenolepis nana (Dwarf tapeworm)
  • Hymenolepis diminuta (Rat Tapeworm)

  
• Dipylidium caninum


  Dog Tapeworm/Double-Pored Tapeworm (Flea Tapeworm)/Cucumber Tapeworm

  
• Dipylidium caninum


  • Proglottids have double set of reproductive organs and genital pore on each side of the lateral margin
  • The only parasite with two sets of reproductive organs
  • Mature and gravid proglottids are typically shaped like melon seeds/pumpkin seeds/rice grains/cucumber
  • Common tapeworm of the dog and cat; man is an accidental host (ingestion of fleas containing the larva)
  • Habitat: Small Intestine
  • Final Host: Dog
  • Accidental Host: Man
  • Intermediate Host: Flea (Ctenocephalides canis - dog flea, Ctenocephalides felis - cat flea, Pulex irritans - human flea)
  • Infective Stage: Cysticercoid Larvae
  • Mode of Transmission: Ingestion of the flea
  • Eggs: Enclosed in an egg capsule/egg packets (8-15 embryonated eggs; looks like Taenia egg)
  • Adult Scolex: Conical shaped, armed rostellum

  
• Echinococcus granulosus


  Hydatid Worm

  
• Echinococcus granulosus


  • Shortest tapeworm of man, with only three segments: immature, mature, gravid
  • Causes Hydatid Disease (Anti-P1)
  • Habitat: Small Intestine (Final Host); Connective Tissues (Man/Accidental Intermediate Host)
  • Final Host: Dog (Canine, Foxes)
  • Intermediate Host: Sheep (Herbivores)
  • Accidental Intermediate Host: Man
  • Infective Stage: To Final Host - Hydatid Cyst, To Intermediate Host - Egg
  • Mode of Transmission: Ingestion of egg (will develop into hydatid cyst in man)
  • Adult Proglottid: 3 proglottids: Immature, Mature, Gravid
  • Eggs: Embryonated like Taenia spp.; cannot be differentiated from the eggs