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Life cycle pattern of parasites

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  1. Plasmodium: malariae, ovale, vivax, falciparum (I)
  2. Ascaris lumbricoides (D)
  3. Giardea spp (D)
  4. Toxoplasma gondi (I)
  5. Schistosoma mansoni (I)
  6. Schistosoma haematobium (I)
  7. Onchocerca vuvolus (I)
  8. Pedicolus humanus par capitis*
  9. Diphilosotrium latum (I)
  10. Wucheletria bancrofti (I)
  11. Taenia solium and taenia saginata (I)
  12. Dracunculus medinensis (I)
  13. Echinococcus granolosus (I)
  14. Tunga penetrans*
  15. Fasciola higutia (I)
  16. Trichuris trichura (I)
  17. Entamoeba histolitica (D)
  18. Enteribious ??? (D)
  19. Heminolopois dana (I)
  20. Ancylostoma biazilonsis (D)
  21. Loa loa (I)
  22. Necator americanus (D)
  23. Leshmenia (I): lobotomous fly transmits it.


Exam question

  • List at least, 10 parasites that have direct life cycle pattern.
  • Draw a schematic diagram showing the life cycle pattern of a named parasite.



  • Know the life cycle pattern of parasites.



  • In all cases of direct life cycle of parasites, soil is the environment that creates the comfortability of a parasite to change its form.


Ascaris lumbricoides (D)

  • The soil is the environment that enables this parasite to change form.
  • The predetermined site is the intestine (gut).
  • These parasites are found in the gut and there, they produce their eggs and they are there for years. The eggs pass out of the feces.
  • Ascaris has a “decuticated” egg; the eggs of ascaris become “embryonated” eggs in the soil. Humans become infected with these eggs by ingestion.
  • The moment these eggs reach the GIT, digesting enzymes digest the shells of these eggs and the embryo (larvae) get into the bloodstream and find their way to the lungs of the infected person. It migrates through the bronchioles to the trachea and causes respiratory disturbances which result in cough and the parasite is swallowed back into the gut thereby maintaining its life cycle.


Dracunculus medinensis (I)

  • Intermediate host is a cyclop/ copepod (an anthropod). It is present in almost every water we drink.
  • 90% of these cyclops come out at the lower extremities.
  • Female cyclops give birth to children via ovoviviparosity; this means the eggs hatch inside the body of the worm and the small children coming out become larvae. This is when the worm comes out to release their larvae into the water.
  • L1: larva from the body.
  • L2: larva in the water.
  • L3: larva inside the water.
  • When the leg of the infected person enters water, the worms and it eggs (larvae) come out. When they are in water, cyclops feed on them and then take the L3 larva of guinea worm. This cyclops is in the water and then humans drink the water. Once the cyclops get into the gut, the cyclops will die and L3 larvae becomes the worm in the body system and causes infection.
  • Infective stage of guinea worm to man is the L3 larvae.
  • Target organ: lower extremities of man. It can be found on the breast, neck and scrotal organ of the man in severe/ extreme cases.


Schistosoma spp (I)


Necator americanus (D)