CESTODES

• Cestodes are classified under the subkingdom Metazoa, phylum Platyhelminthes
• Cestodes are considered as primitive worms
• The body is elongated with a cylindrical or flattened shape
• Tegument - "outer surface" this is how they absorb nutrients and eliminate their waste products
• Cestodes are commonly known as - Tapeworms
• Cestode eggs hatch into larvae called oncospheres which can be ingested by an intermediate host (usually arthropod)
• Morphological features:

  Parasites are flat and consists of three distinct regions:

  >Head /scolex

  >Neck

  >Body/strobila (made up of proglottids)
• Scolex - an organ of attachment in the head 

  - may consists of either hooks, suckers, or sucking grooves
• in some species, the scolex has a fleshy extension called the - rostellum to which hooks may be attached
• Neck - region of growth and connects the head to the body of the worm
• How do worms grow? - by adding new proglottids from the neck
• Where can the oldest proglottids be found? At the most distal part of the body off the parasite
• The body is divided into multiple segments called proglottids
• Series of proglottids - Strobila (plural - strobili)
• How do cestodes reproduce? All cestodes are hermaphroditic (self fertilizing) with each proglotidd containing both ,ale and female reproductive organs
• Each proglottid, therefore is capable of laying eggs (now called a pregnant proglottid or gravid segment)
• A typical cestode life cycle is divided into 3 stages

  >Egg

  >Larva

  >Adult worm
• Infection in humans is usually acquired through - ingestion of the undercooked or raw flesh of the intermediate host containing the infective larvae infection
• After ingestion, the ingested larvae are transformed into adult worms in the intestines of the infected host
• The adult worm then undergoes self-impregnation with the gravid segment rupturing to release the eggs in the intestine.
• The eggs are then passed out to the external environment during defecation
• Intestinal cestodes:

  Taenia saginata

  Taenia solium

  Diphyllobothrium latum

  Hymenolepis nana
• Extra intestinal cestode:

  Echinococcus granulosus
• Taenia saginata - beef tapeworm
• Taenia saginata - intermediate host - cattle -> eggs enter the blood vessels within their intestines
• Cycle of taenia saginata

  1. Eggs or gravid proglottids in feces and passed into environment
  2. Cattle - constipated by eating vegetation contaminated by eggs and gravid proglottids
  3. Oncospheres hatch, penetrate intestinal wallm and circulate to musculature
  4. Oncospheres develop into cysticerci in muscles (infective stage)
  5. Humans become infected by ingesting raw or undercooked infected meat
  6. Scolex attaches to intestine
  7. Adults in small intestine
• Majority of cestodes - the egg contains an embryo - oncosphere - represents the first larval or motile stage
• Oncosphere - equiped with small hooks (hooklets) that eventually enable the parasite to pierce the wall of the intestines
• Eggs are excreted in the feces and are transmitted to the intermediate hosts
• Taenia saginata - endemic - eastern Europe, Russia, eastern Africa, and latin america
• Taenia saginata - adult worm - do not produce significant damage in the small intestine
• Taenia saginata

  -> Disease: Taeniasis

  • majority asymptomatic
  • Those with high worm burden may complain of (1)diarrhea, (2)abdominal pain, (3)loss of appetite with resultant (4)weight loss, and (5)body malaise
• Taenia saginata

  ->Disease:Taeniasis

  • Gravid proglottids may reach the anus where egg-laying may occur -> itchiness of anal region (pruritus ani)
• Taenia saginata

  Laboratory Diagnosis

  • Examination of fecal specimen from infected patients
  • Eggs Or gravid proglottids may be recovered from the stool although eggs are less often found than the proglottids
• Taenia solium - Adult worm - causes cysticercosis
• Taenia solium - endemic - worldwide but more common in developing countries
• Taenia solium - pork tapeworm
• Taenia solium

  Infection is acquired - ingestion of improperly cooked or raw pork meat which contains the infective larvae - cysticercus cellulosae
• Unlike beef tapeworm, taenia solium infection can also occur - ingestion of food or water contaminated with human feces that contain the eggs of the parasite
• Taenia saginata - 1 mode of infection - ingestion of raw or undercooked infected beef meat

  Taenia solium - 2 mode of infection - ingestion of raw or undercooked infected pork meat, and ingestion of water ad food contaminated with infected human feces