Organisms Affecting Human Health Part 2

Organisms Affecting Human Health Part 2

20.9 Some common parasitic worms
Some common parasitic worms are round worms, thread worms, liver fluke and tapeworms.
Roundworms (nematodes)
Ascaris is a common roundworm. It is 20-30 cm long and is pinkish white in colour.

These worms live in the small intestine of man and move freely. The major symptoms of the disease are abdominal pain, dyspepsia, anxiety, nausea, and coughing. The eggs of ascaris are excreted in soil along with feces. These eggs can enter another person, due to unhygienic conditions. When these eggs reach small intestine, they develop into new worms and cause disease.

This disease is more common in children as compared to adults and children are source of its spread.
In this disease, as the worms feed on the food of the patient, that is why patient suffers from malnutrition.

Fig. 20.12

Thread worms

Thread worms are very small only ½ inch long. Both male and female worms live in the colon of human beings. At night the female descends the colon and lays her eggs in the folds of skin about the anus. This causes intense itching, if the anus is scratched, the eggs stick to the fingers and thus transferred to the mouth or deposited on cutlery and household utensils. The eggs also become attached to the clothing and the bedding. When these articles are shaken, the eggs are dispersed in the air and may be breathed in. the eggs pass to the stomach and to the large intestine and develop into adult thread worms. Children are mainly affected by these worms. Drugs can be given to get rid of worms.

Liver fluke (platyhelminthes)

The fluke are flat worms. They are the parasites of both man and animal. All flukes require at least two hosts to complete their life cycle. One of the fluke is liver fluke. It lives in and feeds in the liver of the human beings, where it causes much damage. The eggs of the fluke pass out in the faeces of infected person and thus they may come to the freshwater. Snails living in the freshwater eat the eggs. The eggs develop and form larva in the snails. The larva develops into small creature with a tail. At this stage they leave the snail and swim into water and seek a fresh host.

Their next host is freshwater fish. The embryos penetrate the skin and enter the muscles of the fish. In the muscles the embryo forms a hard protective layer and become cysts. These cysts are very hard and are only destroyed by a thorough cooking of the fish. When partially cooked fish is eaten by man, the cysts arrive in the stomach and there they develop. From the stomach the parasites pass to the liver, where they grow to adult flukes. The adult flukes are both male and female, they come together and fertile eggs are produced and the cycle is repeated (fig. 20.13).

Drugs for the treatment are available but the best way is to improve sanitation.

Fig. 20. 13 life cycle of liver fluke

Tapeworms (Taenia solium)

Flat worms are largest organisms to parasitize human beings. They are called flat worms because of their flattened bodies. All tapeworms are parasites and require at least two hosts to complete their life cycle.

Tapeworms have a small head on which suckers and sometimes hooks are present to attach them to their host’s intestine. Their length varies from few centimeters to 10 meters and their body is made of segments called proglottids. They are hermaphrodite i.e. each proglottid has both sexes.

The life cycle of tapeworm involves two hosts. Primary host is the one in which the adult tapeworm lives and reproduces. And secondary host is an animal, which is eaten by the primary host for example beef tape worm’s primary host is humans and secondary host is cattle. If the sewage disposal conditions are not proper, tape worm eggs may be eaten by a cow while grazing. Because of the digestive juice of cow in the gut, larvae come out of the eggs which then find their way into the muscular tissues. There they remain unchanged for several years. If the partially cooked cow meat of infested cow is eaten by humans the larvae are activated by digestive juices, where they manage to attach the intestinal wall with their suckers or hooks. There the larvae develop into adult tapeworms. After fertilization sex organs disappear and are replaced by thousands of microscopic proglottids. At this stage proglottids drop from the tape worm and pass out of the host’s body with faeces (fig 20.14).

Fig 20.14 life cycle of tapeworm