Ascaris lumbricoides

  • Ascaris lumbricoides lives in the intestines of a man or pig, feeding on the digested food of the host.
  • The body of the worm is tapered at both ends.
  • The female is longer than the male.

Mode of transmission

  • The host eats food contaminated with the eggs, the embryo worms hatch out in the intestine.
  • The embryo worms then bore into the blood vessels of the intestine.
  • They are carried in the bloodstream to the heart and then into the lungs.
  • As they travel through the bloodstream, they grow in size.
  • After sometime, the worms are coughed out from the air passages and into the oesophagus.
  • They are then swallowed, eventually finding their way into the intestines where they grow into mature worms.

Effects of Ascaris lumbricoides on the host

  • The parasites feed on the host’s digested food.
  • This results in malnutrition especially in children.
  • If the worms are too many, they may block the intestine and interfere with digestion.
  • The worms sometimes wander along the alimentary canal and may pass through the nose or mouth.
  • In this way, they interfere with breathing and may cause serious illness.
  • The larvae may cause severe internal bleeding as they penetrate the wall of the intestine.

Adaptive Characteristics

  • The female lays as many as 25 million eggs.
  • This ensures the continuation of the species.
  • Eggs are covered by a protective cuticle that prevents them from dehydration.
  • The adult worms tolerate low oxygen concentration.
  • Have mouth parts for sucking food and other fluids in the intestines.
  • Has a thick cuticle or pellicle to protect it from digestive enzymes produced by the host.

Control and Prevention

  • Personal hygiene e.g. washing hands before eating.
  • Proper disposal of faeces.
  • Washing of fruits and vegetables.


  • Deworm using appropriate drugs ¬ant-helmintics.


  • Schistosoma or bilharzia worm is a flat worm, parasitic on human beings and fresh water snails. (Biomphalaria and Bulinus.)
  • The snail act as intermediate host.

Mode of Transmission

  • Schistosomiasis also known as a bilharsiasis is caused by several species of the genus schistosoma.
  • Schistosoma haematobium ¬infects the urinary system mainly the bladder
  • japonicum and S. mansoni both infect the intestines.
  • Schistosoma haemotobium is common in East Africa where irrigation is practised and where slow moving fresh water streams harbour snails.
  • It is spread through contamination of water by faeces and urine from infected persons.
  • The embryo (miracidium) that hatch in water penetrates into snails of the species Biompharahia and Bulinus.
  • Inside the snail’s body, the miracidium undergoes development and multiple fission to produce rediae.
  • The rediae are released into the water and develop to form cercariae which infect human through:
  • Drinking the water
  • Wading in water;
  • Bathing in snail-infested water.
  • The cercaria burrows through the skin and enters blood vessel.

Effects on the host

  • Inflammation of tissues where egg lodge.
  • Ulceration where eggs calcify.
  • Egg block small arteries in lungs leading to less aeration of blood.
  • The body turns blue – a condition known as cyanosis.
  • If eggs lodge in heart or brain, lesions formed can lead to death.
  • Bleeding occurs as the worms burrow into blood vessels (faeces or urine has blood).
  • Pain and difficulty in passing out urine.
  • Nausea and vomiting.
  • When eggs lodge in liver ulceration results in liver cirrhosis.
  • Death eventually occurs.
See also  Growth and Development in Animals

Adaptive Characteristics

  • The female has a thin body and fits into small blood vessels to lay eggs.
  • Eggs are able to burrow out of blood vessel into intestine lumen.
  • Many eggs are laid to ensure the survival of the parasite.
  • Large numbers of cercariae are released by snail.
  • The miracidia and cercariae larvae have glands that secrete lytic enzymes which soften the tissue to allow for penetration into host.
  • The male has a gynecophoric canal that carries the female to ensure that eggs are fertilised before being shed.
  • Has suckers for attachment.

Prevention and Control

  • Drain all stagnant water
  • Boil drinking water.
  • Do not wade bare feet in water.
  • Wear long rubber boots and gloves (for those who work in rice fields).
  • Eliminate snails, by spraying with molluscides.
  • Reporting to doctor early when symptoms appear for early treatment.

See also:






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