More cestodes

• Digenetic trematodes


  Those which require an intermediate molluscan host, commonly called flukes
• Families of Trematoda with major veterinary and agricultural importance

  • Fasciolidae
  • Dicrocoeliidae
  • Paramphistomatidae
  • Schistosomatidae
• Fasciola hepatica


  • Two suckers anteriorly and ventrally
  • Pharynx dividing into complex gut caeca
  • Excretory ducts (outside caeca) run into excretory "bladder" and thence to excretory pore (no anus from the gut)
  • Vitelline glands and shoulders
• Encysted cercariae (metacercariae) of Fasciola hepatica


  • Each cyst is about 0.2 mm in diameter
• Lymnaea truncatula


  • Intermediate host of Fasciola hepatica
  • Lymnaeid snails are termed "dextral": the aperture of the shell, when facing the observer, is on the right when viewed with the spire upward
  • The aperture is also approximately half the length of the entire snail
• Platynosomum fastosum


  • A small liver fluke of cats in the Caribbean, North and South America and other part of the world
  • Infection occurs when cats eat infected reptiles especially lizards (Anolis spp.)
• Cestoda


  Class of tapeworm-like worms with no alimentary canal, body is segmented with male and female reproductive organs
• Taeniidae


  • Adults parasitise domestic carnivores and man
  • Scolex has an armed rostellum with concentric double rows of hooks (except T. saginata)
  • Gravid segments are longer than they are wide
  • Intermediate stages are cysticercus, strobilocercus, coenurus, hydatid, cysticercoid or tetrathyridium
• Tapeworm scolices

  • Armed and unarmed
• Tapeworm proglottids


  • Note the shape and unilateral genital pore alternating irregularly
• Tapeworm eggs


  • Note the onchosphere and the thick dark radially striated "shell" called the embryophore
• Whole tapeworms

  • Scolex and immature segments
  • Mature segments
  • Gravid segments
• Cysticerci

  • Pea-sized cysticercus consisting of a fluid filled bladder containing an invaginated scolex
• Metacestode of Taenia multiceps is called Coenurus
• Echinococcus

  • Adult measures 3-6 mm, consists of a scolex and 3-5 segments
  • Large gravid terminal segment, half the length of the entire worm
• Echinococcus larvae

  • Hydatid cyst
• Hyatid "sand"


  • Gross appearance
• Dipylidium caninum


  • Characteristic barrel-shaped gravid segments
  • Commonest tapeworm of the Trinidad dog
• Dried proglottids of Dipylidium

  • Note the sesame seed appearance
• Dipylidium caninum egg capsule


  • From crushed segments
• Raillietina

  • Has the armed rostellum and suckers, found in local poultry
• Davainea

  • Smaller but more pathogenic tapeworm
• Pseudophyllidea


  • Scolex has no suckers but two longitudinal grooves or bothria which become flattened to become organs of attachment
  • Egg shell is thin and operculate
  • Coracidium which emerges after hatching is an onchosphere with an embryophore which is ciliated for mobility in water
• Diphyllobothrium latum


  • Found on man and any fish eating mammals (dog, cat, pig and polar bears)
  • Adult up to 20m in length, mature segments are square shaped
• Spirometra mansoni

  • Adult worm measures 60-100cm, found worldwide in dogs and cats (DH) and aquatic organisms such as fish, reptiles, amphibians and crustaceans (IH)
  • Humans can also serve as secondary IHs where it causes a disease known as sparganosis
• Spirometra mansoni plerocercoid larva (sparganum)

  • Can migrate to tissues such as the subcutaneous tissue, orbit, breast, pleural cavity, lungs, abdominal viscera, urinary tract, CNS of the intermediate host