Helminths

• Helminths


  Worm-like parasites
• Helminths


  • All are relatively large (> 1 mm long); some are very large (> 1 m long)
  • All have well-developed organ systems and most are active feeders
  • Worms are often long-lived
• Clinically relevant helminth groups

  Separated according to their general external shape and the host organ they inhabit
• There are both hermaphroditic and bisexual helminth species
• Helminth classification

  Based on the external and internal morphology of egg, larval, and adult stages
• Helminths are worldwide in distribution; infection is most common and most serious in poor countries
• Helminth disease distribution

  Determined by climate, hygiene, diet, and exposure to vectors
• Modes of helminth transmission

  • Ingestion of eggs or larvae
  • Penetration by larvae
  • Bite of vectors
  • Ingestion of stages in the meat of intermediate hosts
• Many helminth infections are asymptomatic; pathologic manifestations depend on the size, activity, and metabolism of the worms
• Flukes (Trematodes)


  • Adult flukes are leaf-shaped flatworms
  • Prominent oral and ventral suckers help maintain position in situ
  • Hermaphroditic except for blood flukes, which are bisexual
  • Life-cycle includes a snail intermediate host
• Tapeworms (Cestodes)


  • Elongated, segmented, hermaphroditic flatworms that inhabit the intestinal lumen
  • Larval forms, which are cystic or solid, inhabit extraintestinal tissues
• Roundworms (Nematodes)


  • Adult and larval roundworms are bisexual, cylindrical worms
  • They inhabit intestinal and extraintestinal sites (Loa loa – filarial)
• Roundworms (Nematodes)

  • Ascaris lumbricoides That can cause Ascariasis

  ➢ Largest SI worm (Jejunum & Ileum)

  ➢ Children

  ➢ 85% Asymptomatic

  ➢ Fever

  ➢ Abdominal pain

  ➢ Diarrhea

  ➢ Malnutrition

  ➢ Learning difficulties

  Tx: • - Albenzadole • - Mebendazole • - Pyrantel pamoate
• Schistosomiasis


  A disease caused by flukes
• Ascariasis


  A disease caused by roundworms / nematodes
• Schistosomiasis

  • Snail fever / Bilharzia / Katayama fever
  • Itchy rash (swimmer’s itch)
  • Abdominal pain, dysentery, hematuria 🡪 liver & renal failure, bladder cancer
• Important Cestodes

  Taenia saginata : Beef tapeworm

  Taenia solium : Pork tapeworm

  Echinococcus granulosus: Dog tape worm

  Taenia asiatica: Asian tapeworm

  (morphology close to T.saginata; life cycle similar to T.solium))

  Diphyllobothrium latum: Fish tape worm

  Hymenolepis nana: Dwarf tape worm
• • Mode of Transmission ( Cestodes )Ingestion of raw or under cooked Beef (T.saginata) or Pork (T.soilum) with encysted larval stagecysticercus