Roundworm





The disease which is caused by Ascaris in man is known as Ascariasis. The Ascaris is commonly known as Roundworm, because this worm is round and elongated but pointed in both ends. Ascaris lumbricoides is the full scientific name of the roundworm. It is most commonly intestinal worm in man. It belongs to the phylum Aschelminthes. It lives as an endoparasite in the lumen of small intestine of man. Ascaris lumbricoides is more common in the children than in the adults. It is not surprising to found as many as about 5000 adult worm in a single human being.

Roundworm

Roundworm


Male and female sexes are separate in the roundworm Ascaris lumbricoides and clear sexual dimorphismis present. The female Ascaris is about twenty to forty centimetre long and about six to eight millimetre in diameter and the posterior end of it is almost straight. The male Ascaris is smaller in comparison of the female but the posterior end of the body is sharply curved in the male. If a fresh specimen is taken Ascaris lumbricoides is creamy or pinkish in color.



Modes of Development and transmission of Roundworm:

The adult male and female roundworm copulate inside the intestine of the host, generally the man and the ova are fertilized eggs are encapsulated by chitinoid shells. Large number of fertilized encapsulated eggs is laid by the female worm inside the small intestine of the host and from there they pass out of the host’s body along with the stool of the host. Outside the host’s body, these encapsulated eggs develop into the inactive stage in the faeces of the host.

Development of infective stage to new host :

these encapsulated eggs of roundworm with infective stage are ingested by new host that is man along with food or water. But in the stomach of host there is no liberation of larva. When these are coming to the small intestine of the host, the shell of the eggs dissolve and second juvenile stage is liberated. This juvenile stage is closely related to Rhabditiform larva.




Migration and development of larvae :

These larvae of roundworm bore through the intestinal wall of the host and enter to the hepatic portal vein and then come to the liver. After that, from the liver they come to the right side of the heart through the post caval vein. From the heart, they are carried in the lungs via pulmonary arteries.In the lungs two successive moults occur and the 4th stage larvae are developed. These larvae come to the throat through bronchioles and trachea. From the throat they are swallowed into the esophagus and finally, these larvae reach the intestine again. Here fourth moulting occurs and as a result the larvae become adult.

Modes of Infection by Roundworm :

Infective stage of Ascaris Lumbricoides transmission is direct without the intermediate host. But it is to remember that the Man is the final host of roundworm. So this infective stage of Ascaris is transferred from man to man. Man may attacked by the infective stage in the following way : -

i) If contaminated night soil of man is used as fertilizer in the vegetable field, the embryonated eggs of Ascaris remain attached to these vegetables. When man ingest these contaminated food materials without proper cleaning the man can easily infected by the roundworm.
ii) Contaminated drinking water may contain infective stage of Ascaris and man can be easily infected.
iii) Sometimes soil is polluted by infective stage of Ascaris. If this type of infected soli remains attach to the nails of man and the man unconsciously placed fingers inside the mouth and as a result infected by the worm.
iv) Sometimes, the infected stage of Ascaris is floating on dust particles. During inspiration they may enter to the pharyngeal region of man and then they get easily entry to the intestine.