HUMAN DISEASES (PARASITIC DISEASES)
- 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.
- 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.
- 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.