LIFE CYCLE OF TAENIA SOLIUM
WATCH THIS VIDEO FOR LIFE CYCLE OF TAENIA SOLIUM
Taenia solium completes its life cycle in two different vertebrate hosts , man and pig.
Man is considered to be the definitive host and
the pig is considered as the intermediate host.
The life cycle of taenia solium includes
2. The human phase,
3. The pig phase.
1. Fertilization occurs in the ootype.
2. In taenia solium both self – fertilization and cross – fertilization occurs in tapeworm.
3. In self fertilization , sperms produced in proglottid in a proglottid fertilize the ova produced in the same proglottid.
4. In cross fertilization , sperms produced in a proglottid fetilize ova produced in another mature proglottid of the same worm.
5. As a result of fertilization, zygotes are formed.
6. A yolk cell or vitelline cell is attached to each zygote.
7. Later, the vitelline gland secretes a shell around these two cells.
8. Such a shell bearing zygote is called capsule.
9. These capsules now roll up into the uterus. This is facilitate4d by a ubricating substance secreted by Mehli’s glands.
10. The uterus develops lateral branches and occupies almost the entire space in the proglottid as thousands of capsules enter into it. Such proglottids are called gravid proglottids .
11. These gravid proglottids are discharged through faeces of the host by the process apolysis.
2.THE HUMAN PHASE:
1. The embryonic development of Taenia solium begins in the uterus itself.
2. The zygote cell in the capsule undergoes an unequal cleavage and forms a megamere and an embryonic cell.
3. Through unequal divisions , the embryonic cell forms mesomeres and micromeres.
4. The micromeres undergo further cleavages and develop into a ball of cells called morula, which later becomes the embryo.
5. The mesomeres surrounding the embryo form an inner embryonic membrane or embryophore.
6. The megamere also devides and these cells form the outer embryonic membrane outside the embryophore.
7. The vitelline cell provides nourishment to the embryo during embryonic development.
8. The oncoblasts of the embryo secrete six chitinous hooks. In the embryo, these hooks are arranged in three pairs. The embryo with six hooks is called hexacanth embryo.A pair of penetration glands is present in the hexacanth .
9. The hexacanth , which is surrounded by two embryonic membranes , is called oncosphere.
10. In each gravid proglottid , the uterus shows 7-10 lateral branches on each side. 30,000 to 40,000 oncospheres are stored in these branches in each proglottid. Such gravid proglottides are discharged out by apolysis..
3.THE PIG PHASE:
1. infection of the intermediate host , the pig (sus scrofa) , takes place by the oncosphere stage.
2. The gravid proglottides containing oncospheres are present in the human faeces.
3. When a pig takes such faecal matter as food the gravid proglottides enter the stomach and oncospheres are released into the stomach.
4. In the stomach of the pig , the shell and embryonic membranes of the oncosphere are digested and the hexacanth larva is set free.
5. These free hexacanth larvae pass into the intestine and attach to the mucous layer of the intestine with the help of its hooks.
6. they penetrate the intestinal wall with the help of the substances secreted by the penetration glands.
7. Later, hexacanth larvae enters the hepatic portal vein through which it goes to the liver. From the lever it goes to the heart through post caval vein. From the heart , it goes to the voluntary muscles of pig.
8. Generally, the hexacanth settles in the voluntary muscles of the tongue , elbows,neck and limbs.
9. Some times , the hexacanth may also enter organs like lungs, eyes, kidneys , brain etc.,
10. The hexacanth loses its hooks in the voluntary muscles of the pig.It develops into cysticircus larva.
11. This early cysticircus larva absorbs nutritive substances from the tissues and grows in size.
12. A cavity appears in the centre of the cell mass due to disintegration of mesenchyme and is get filled with a liquid material.This liquid contains large amount of plasma of the host blood(pig).
13. At this stage , the embryo is surrounded by two layers, the outer cuticle and the inner mesenchymal layers or germinal layer.
14. The wall of the embryo of the on one side gets thickened and invaginates into its cavity, in the form of a knob.
15. The knob internally develops four suckers ,a small rostellum and hooks at its base. This inverted scolex is called proscolex. Now the embryo is the mature cysticircus, or bladder worm.
16. The cysticircus is an ellipsoid miky whitish bladder surrounded by fibrous capsule. Now these cysts are called Cysticircus cellulosae, as they appear to cover by cellulose cyst wall.
17. It requires about 10 weeks time for the transformation of hexacanth into mature cysticircus larva.
18. the pork with cysticircus larvae shows light brown patches , such pork is termed measly pork.
19. Cysticircus larva does not undergo further development in the muscles of pig. In this stage it can survive in pig for 5or 6 years and dies if it is not transferred to man within this period.
20. When man consumes improperly cooked measly pork, the cysticircus reaches the stomach.
21. In the stomach the fibrous capsule of the bladder is dissolved by the action of digestive enzymes.
22. This stage now reaches the intestine. The proscolex evaginates and forms the scolex. With the help of suckers and rostellar hooks, it attaches to the wall of the intestine.
23. New proglottides begin to proliferate from the neck region and the bladder gets disintegrated. It develops into an adult tapewotm within two or three months.
Parasitic adaptations in Taenia solium:
Taenia solium exhibits the following parasitic adaptations in its structure:
1. Absence of digestive system.
2. Presence of an enzyme resistant tegument .
3. Presence of hooks and suckers for attaching to the host.
4. Presence of complex reproductive organs.
WATCH THIS VIDEO FOR CYSTICERCOSIS
The adult tapeworm and the cysticircus larvae are harmful to man.
In man taenia solium causes taeniasis and cysticircus causes cysticircosis.
Adult tapeworm causes taeniasis . Its sympyoms include pain in abdomen ,anaemia, giddiness, obstruction to passage of food, vomiting,indigestion and oesinophilia(allergic reactions include the increase in the number of oesinophils).
The infection of oncospheres to man causes cysticircosis. This infection is due to the contamination of food and water with oncospheres. When the scolex of taenia solium causes injury to the intestinal wall, it triggers reverse peristalsis. As a result , some gravid proglottides are pushed back in to the stomach. This process is called autoinfection. The oncospheres released from the gravid proglottides ultimately reach the voluntary muscles and transform themselves into cystisircus larvae. They form cysts in heart,brain,eyes,liver and muscles. In the brain it causes necrosis resulting in the disintegration of living cells. Epilepsy is the most common manifestation in cysticircosis. This disease is more dangerous than taeniasis. It is seen mostly in children.
PROPHYLAXIS or PREVENTION
Prophylactic measures include the following ,
1. Pork should be properly cooked.
2. Selling of measly pork should be prohibited.
3. defeacation by human beings in open places should be discourged.
4. Proper hygienic habits should be maintained.