Tapeworm

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Taeniasis is the disease caused by Taenia in man. This disease is mainly caused by two species; those are Taenia solium and Taenia saginata. They are commonly known as Tapeworm as they segmented ribbon shaped worm. They inhabit intestinal tract of man as endoparasite. They have not any alimentary system and absorb nutrition through their surface from the host. They are included in the phylum Platyhelminthes. In case of Taenia solium, developmental stages are taking place in the body of Pig. Due to this, the parasite is commonly known as Beef tapeworm.

So, it is easy to understand that Taenia solium occurs in most pork-eating persons and Taenia saginata occurs in most beef –eating persons. These parasites are regarded as digenetic parasites, as they require two hosts, such as man and pig in case of Taenia solium and man and cattle in case of Taenia Saginata.

A beef –tapeworm, the Taenia saginata is several metres long (4 to 8 metres); but a pork-tapeworm, the Taenia solium is not so large as beef-tapeworm and it is about two to three metres long. The anterior end of the worm is known as scolex. This pin head scolex is provided with suckers, which is used for the attachment to the human intestine. In case of pork-tapeworm, the scolex has, in addition to suckers, two circular rows of hooklets anterior to the suckers.




There is a short, narrow and un-segmented region at the posterior end of the scolex, which is known as neck. New segments are developed from neck. For this reason the neck region is known as proliferative zone or growth zone. Behind the neck there is bulk of segmented body known as . In case of Taenia saginata the strobila is formed by 1000 to 2000 segments but in the case of Taenia solium the strobila is formed by 800 to 1000 segments. These segments are called as proglottides. These proglottides are iof three types, those are (i) immature, (ii) mature and (iii) gravid. In each mature proglottides, both male and female reproductive organs are present. Due to this Taenia is regarded as hermaphrodite.

Modes of Development and Transmission of Tapeworm :

In general, single tapeworm is residing in the lumen of alimentary cannel of a primary host, i.e. Man. So self fertilisation occurs in the same proglottid of the tapeworm and fertilisation takes place in the Ootype of the female organ. Fertilized egg develops a thick hard radially striated embryophore, inside of which the embryo is developed. Six numbers of chitinous hooks contains in this embryo. This six-hooked embryo is called hexacanth. The hexacanth embryo together with basement membrane , embryophore and the outermost egg shell constitute the onchosphere. Later on, the onchosphere loses its shell membrane. Hence the embryophore remains as an outermost covering of the onchosphere. So about thirty to forty thousand onchosphere are formed in the lateral branches of of the uterus, by the time the mature proglottides become gravid proglottides. The gravid proglottides in group of five to seven are detached from the terminal part of strobila which is called apolysisand pass out with the stool of primary host, i.e. Man.

Infection to Secondary Host:

The gravid proglottides or onchospheres may be eaten by secondary or intermediate host (i.e. pig)due to its coprophagus habit. Then the membranes of the onchospheres are dissolved in the stomach and intestine of the pig and the hexacanth embryo is released. The hexacanth embryo bores through the intestine and enters into the blood vessel of the host. In this way the embryos circulated through the heart and finally reach the muscles of the pig’s body. In the muscles of pig’s neck, shoulder and thigh the hexacanth develop into the cysticcercus stage.

Infection to Primary Host (i.e. Man) :

The parasite, cysticeric is finally transferred to the main host, which is Man, by ill cooked measly pork. So the cysticercus is the infective stage to man. After that within the intestine, the bladder of the cysticercus is thrown off and the scolex gets attached to the intestine of man and then the parasite starts growing and new segments are developed. The time taken by the Taenia becomes fully matured tapeworm is about 2 to 3 months.

Mode of infection by Tapeworm:

In case of pork eaten persons, the cysticercus is transferred when pork is eaten by man in half cook or under cook condition. Then the cysticercus enters to the small intestine and anchors to the intestinal wall.
Sometimes, self infection in man by contaminated food or fingers or by regurgitation of ova with onchosphere stage from the intestine. In the stomach of man the shells of ova are digested and the larvae, which are liberated from the eggs, penetrate the intestine and are carried many parts of the body or in the brain where they develop and form cysticerci.