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In this article we will discuss about Taenia Solium:- 1. Structure of Taenia Solium 2. Reproductive Organs of Taenia Solium 3. Fertilization and Development 4. Life History.
Structure of Taenia Solium:
1. Body of Taenia Solium is ribbon-like, 2-3 meters long and consists of about 800-900 segments known as pro-glottides (Fig.22).
2. The pear-shaped head bears 28 curved chitinoid hooks arranged in two rows, and four adhesive suckers.
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3. Just behind the head there is a small un-segmented region which may be called the neck.
4. Each proglottis is a complete hermaphrodite sexual unit.
Reproductive Organs of Taenia Solium:
1. The reproductive organs of Taenia Solium first appear at about 200th segment; the male part of the reproductive system appears first, becomes mature at about 400th segment, and the posterior segments are filled up with greatly increased uterus, heavily loaded with developing embryos.
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2. The male organs of Taenia Solium consist of a much lobed testis with efferent ducts, vas deferens and cirrus, opening in the genital atrium by the male genital aperture.
3. The female organs of Taenia Solium consist of a paired ovary with their ducts, uterus, yolk glands with ducts, shell glands with ducts, ootype, receptaculum seminis and the vagina opening in the genital atrium through the female genital aperture.
4. With the development of the uterus, the other reproductive organs are degenerated and the gravid uterus looks like a longitudinal stem with 5-10 lateral branches.
Fertilization and Development in Taenia Solium:
1. Eggs are fertilized in the oviduct and self or cross fertilization may take place.
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2. The zygote becomes surrounded by yolk and a chitinoid egg shell, and passes to the uterus.
3. The ripe proglottides loaded with developing embryos get detached in chains of 5 or 6, and pass to the exterior with the faeces of the host.
4. The proglottides are eaten up by pig; muscles of the segments get digested and six-hooked or hexacanth embryos are liberated.
Life History of Taenia Solium:
Hexacanth embryo or onchosphere (Fig.23):
(a) The body of Taenia Solium is rounded and enclosed in two membranes.
(b) Six curved chitinoid hooks are present at one end.
5. The embryos bore the wall of the gut of the host with the hooks and reach the voluntary muscles where the hooks are lost. The embryo then enters the general circulation, usually through the portal vein and reaches the following organs in succession → liver → right side of the heart → lungs → left side of the heart → the systemic circulation. The embryo is filtered out and finally enters the muscular tissue.
6. Here the embryo increases greatly in size, having a large cavity filled up with watery fluid and assumes a bladder-like structure.
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7. A hollow invagination or ingrowth takes place at one point of the bladder and on the inner surface of this invagination develop 28 hooks and 4 suckers, characteristic of the head of adult Taenia.
8. The hollow ingrowth becomes everted and the suckers and hooks come close to the surface.
9. The embryo now looks like a bladder with a head and neck of Taenia lying within it. This is known as bladder worm or cysticercus stage. It is rich in salt and albuminous material and when the pig’s flesh is infected with the cysticercus cellulose, it is known as measly pork.
10. If a portion of measly pork is eaten by man, the bladder is dissolved in the gastric juice. The gastric juice causes the albuminous material to swell up and forces the fluid into the cavity, thereby the head comes out through the pore. The scolex attaches itself to the wall of the intestine by hooks and suckers and develops the series of proglottides to reach the adult stage.
11. The worm gains sexual maturity by 2-3 months-time, and survive for 25 years or more.