CESTODES

• Cestode life cycle

  1. Egg

  2. Larval stage(s)

  3. Adult worm
• Cestodes


  • Flat or ribbon-like appearance
  • Absorb nutrients and excrete waste through outer surface (tegument)
  • Lack sophisticated body parts and systems like mouth, digestive tract, and internal means of excretion
• Scolex

  Defined anterior end of cestode
• Neck region


  Region of cestode between scolex and strobila
• Proglottids


  Individual segments of cestode strobila that contain reproductive organs
• Strobila

  Series of proglottids in a cestode
• Suckers


  Cup-shaped structures on scolex that allow cestode to attach to host intestinal mucosa
• Rostellum


  Fleshy extension of scolex that may have hooks
• Gravid proglottids


  Proglottids containing a uterus filled with eggs
• Cestodes are hermaphroditic, so human ingestion of a single egg can initiate a new life cycle
• Most cestodes require at least one intermediate host for their life cycle to continue
• Development of a cyst in tissue occurs in the intestinal-extraintestinal cestode species Echinococcus granulosus
• The primary specimen for recovering and identifying intestinal tapeworms is stool
• Serologic tests are available for select cestode organisms
• Many patients infected with intestinal cestodes remain asymptomatic
• Symptoms of cestode infection

  Vague gastrointestinal discomfort, diarrhea, abdominal pain, nausea, dizziness, headache, weight loss, intestinal obstruction, vitamin B12-induced macrocytic anemia
• Symptoms of Echinococcus granulosus infection


  Persistent cough, localized pain, eosinophilia, liver and lung involvement
• A serious allergic response known as anaphylactic shock may develop in cestode infections
• Intestinal cestode species

  • Taenia saginata
  • Taenia solium
  • Hymenolepis diminuta
  • Hymenolepis nana
  • Dipylidium caninum
  • Diphyllobothrium latum
• Intestinal-extraintestinal cestode species

  • Echinococcus granulosus
• Taenia saginata

  Beef tapeworm
• Taenia solium

  Pork tapeworm
• Taenia saginata vs Taenia solium

  • Taenia saginata lacks rostellum and hooks, has 15-30 uterine branches per side, and proglottids are longer than wide

  Taenia solium has rostellum and double crown of hooks, has 7-15 uterine branches per side, and proglottids are somewhat square
• Taenia eggs are indistinguishable, so speciation requires recovery of a gravid proglottid or scolex
• Infection with Taenia spp.


  Occurs by ingesting raw/undercooked beef (T. saginata) or pork (T. solium) containing cysticercus larva
• T. saginata is found primarily in areas with poor sanitation and routine beef consumption, while T. solium is found worldwide
• Cyst


  Adder-like, thin-walled cyst that is filled with fluid
• Scolex attachment to intestinal mucosa

  1. Occurs after the larva emerges in the small intestine

  2. Maturation into an adult worm occurs
• Adult worm multiplication

  1. Producing numerous eggs

  2. Some eggs passed into the feces
• Egg consumption by proper animal species (cow or pig)

  1. Oncosphere hatches

  2. Oncosphere migrates via the blood to the animal tissue

  3. Converts into the infective cysticercus larval stage
• Human ingestion of infected animal meat

  Initiates a new cycle
• Distribution of T. saginata and T. solium


  • Directly correlates with areas of the world in which the inhabitants do not practice sanitary conditions and beef or pork is eaten on a routine basis
  • T. saginata is found primarily in these types of cosmopolitan areas, whereas T. solium is found worldwide
• Intermediate host


  A cow or pig, depending on the species
• Most people who become infected with Taenia spp. typically remain asymptomatic
• Taeniasis

  Beef or Pork Tapeworm Infection
• Symptoms of Taenia infection

  • Diarrhea
  • Abdominal pain
  • Change in appetite
  • Slight weight loss
  • Dizziness
  • Vomiting
  • Nausea
• Laboratory tests often reveal the presence of a moderate eosinophilia
• The prognosis for Taenia infections is usually good
• Praziquantel


  Effective against the entire adult worm, but not used when there is ocular or central nervous system (CNS) involvement
• Alternative treatments for Taenia infections

  • Paramomycin
  • Quinacrine hydrochloride (Atabrine)