HUMAN DISEASES (PARASITIC DISEASES)

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

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

Effects of Ascaris lumbricoides on the host

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

Adaptive Characteristics

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

Control and Prevention

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

Treatment

Deworm using appropriate drugs ¬ant-helmintics.

Schistosoma

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

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

Effects on the host

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

Adaptive Characteristics

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

Prevention and Control

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