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Term Paper on Taenia Solium


Term Paper Contents:

  1. Term Paper on the Habits and Habitat of Taenia Solium
  2. Term Paper on the External Features of Taenia Solium
  3. Term Paper on the Internal Structure of Taenia Solium
  4. Term Paper on the Nutrition in Taenia Solium
  5. Term Paper on the Respiratory System and Excretory System of Taenia Solium
  6. Term Paper on the Nervous System and Respiratory System of Taenia Solium
  7. Term Paper on the Life History of Taenia Solium
  8. Term Paper on the Parasitic Adaptations of Taenia Solium


Term Paper # 1.Habits and Habitat of Taenia Solium:

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Taenia solium is commonly known as park tapeworm. It belongs to the class cestoda. All the members of the class cestoda are exclusively endoparasites in the alimentary canal. During their life cycle one or two or more intermediate hosts, vertebrates and invertebrates are required in which the tapeworms undergo a phase of development.

The cestodes differ, however, from the members of other two classes (Turbellaria and Trematoda) in the complete absence of a digestive tract. Basically these are long, flat and ribbon like form. Genus Taenia includes several species parasitizing man and domestic animals. Common examples are T. solium and T. saginata. 

Taenia solium is an intestinal parasite of man found attached to its mucosa by the scolex, while the rest of the body lies free. It is most common in the pork eating population of tropical and subtropical regions, where pork is utilized as food without being thoroughly cooked.


Term Paper # 2. External Features of Taenia Solium:

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Shape, Size and Colour:

The body is elongated dorsoventrally flattened and ribbon-like. It is metamerically segmented consisting of linear of almost similar segments.

The size of adult worm varies from 3-5 metres i.e. 9-16 feet, but few are recorded to attain a length of about 8 metres.

The body is opaque white but may be grey, yellow or cream.

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Structure:

The body of taenia is wonderfully adapted for its parasitic life.

It can be divided into the following three parts:

(i) Scolex or Head

(ii) Neck

(iii) Body or strobila

(i) Scolex:

The anterior end of the parasite forms a knoblike scolex which is biradially symmetrical and 0.6 to 1 mm wide being smaller than the pin-head. At the apex is the rounded prominent mobile cone, the rostellum, having about 22 to 32 curved, chitinous hooks, arranged in two rows around the base. The inner row has larger hooks, about 0.14 to 0.18 mm while the outer row has smaller hooks, about 0.11 to 0.14 mm.

Each hook consists of a base or guard by which it is fixed and the conical outwardly directed blade. The long and short hooks alternate with each other. Four hemispherical, highly muscular suctorial organs known as the suckers or acetabula are present at each angle of the quadrangle. The scolex with the help of suckers and hooks, serves as an organ of attachment to the intestinal mucosa of the host. However, it does not serve for catching the food.

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(ii) Neck:

Lying behind the scolex is a short, dorsoventrally flattened and un-segmented. It is also called budding zone, region of proliferation or area of segmentation because new segments are budded off from this region and are pushed back.

(iii) Body or Strobila:

The dorso-ventrally flattened 4 to 6 m long body is known as strobila. It consists of a chain of similar segments called proglottids. A tape worm may contain about 1,000 proglottids. Each proglottid contains a complete set of male and female reproductive organs and a part of excretory and nervous systems.

A new proglottid is produced in the neck region. Thus, the proglottids next to the neck are youngest and those at the posterior end are the oldest. All these vary in their degree of development.

A strobila contains three types of proglottids:

(a) Immature Proglottids:

Roughly first 200 proglottids after the neck are called as immature proglottids. These are newly formed proglottids. They are without reproductive organs. Their length is less than their width.

(b) Mature Proglottids:

Next 400 to 600 proglottids contain fully developed reproductive organs. These are sexually mature and produce sperms and eggs. Each mature proglottid contains a genital aperture. Male reproductive organs develop first. Few anterior mature proglottids contain only the male reproductive organs, while posterior proglottids contain both male and female reproductive organs. These are square in shape.

(c) Gravid or Ripe Proglottids:

Roughly last 200 proglottids are called as gravid or ripe. Their length is much more than their width. They contain branched uterus only. Other reproductive organs disappear. The uterus remains full of fertilized eggs.

Apolysis:

The posteriormost 5 or 6 gravid proglottids detach from the strobila and are expelled out of host body along with host faeces. This process of separation of gravid proglottids is known as apolysis.


Term Paper # 3. Internal Structure of Taenia Solium:

Body Wall:

The body wall consists of tegument basement membrane, musculature and parenchyma.

1. Tegument:

It is the outer thick and resistant layer of the body wall. It is composed of protein impregnated with calcium carbonate and is perforated by numerous channels. Under light microscope, three distinct layers are seen in the integument.

These are:

(i) Outermost comidial layer

(ii) Middle homogenous layer and

(iii) Innermost basement membrane.

Under electron microscope, the outer comidial layer is non-cellular syncytial layer. The outer plasma membrane is produced into microvilli-like folds, the microtriches. Each on the ventral side and extends into all proglottids of the body. The ventro lateral canals are connected with each other in the posterior end of each proglottid.

In the last proglottid these two canals unite together to open to the outside by a single opening. When the proglottids start separating from the strobila the free ends of these stands act as excretory pores.

All the four excretory canals are connected with each other by a ring vessel in the scolex. The excretory canals are lined with cuticle and cilia are not found in them. Lateral of shoots arise from these canals at whose ends the flame cells are present.

2. Flame Cells:

They are irregular shaped cells whose cytoplasm is granular and a nucleus is found in it. A funnel shaped intracellular space is present in the centre of each from cell and connected with the lumen of the canals. The cilia constantly move in the intercellular space.

3. Mesenchyme or Parenchyma:

The space enclosed by the body wall, except for the occupied by the reproductive organs, osmoregulatory structures, muscle fibres and various tissues, is filled with a spongy type of tissue, the parenchyma. Certain syncytially arranged cells form a network. In living animals, the spaces between the cells are filled with fluid. Numerous rounded calcareous bodies composed of concentric layers of calcium carbonate are present in mesenchyme secreted by lime cells.

Except at the two sides in each segment the parenchyma is divided into:

(i) Outer cortical part and

(ii) Inner medullary part by circular muscle fibres of the mesenchymal musculature.


Term Paper # 4. Nutrition in Taenia Solium:

T. solium is totally endoparasite. It lives in the intestine of host. So there is totally absence of alimentary canal in all the stages of its life cycle. The predigested food in host’s small intestine is the chief source of nourishment for tapeworm. Soluble nutrients like glucose, amino-acids, glycerol etc. diffuse in directly through general body surface (tegument).

Some tissue fluids from host are probably absorbed by scolex of tapeworm insinuated deeply into intestinal mucosa. Stored food consists mainly of glycogen and of some lipoid substances. Glycogen content of T. solium by weight is 2.17%. According to Chandler, tapeworm gets its sugar supply from digested food material of a host but proteins and vitamins are made available to the animal from the living tissue of the host by the secretion of the digestive enzymes, which affects the cells.


Term Paper # 5. Respiratory System and Excretory System of Taenia Solium:

Respiratory System:

In case of T. solium, respiration is mainly anaerobic. Glycogen undergoes glycolysis, producing CO2 and fully acids. Steps involved are same as in liver fluke. In addition to fatty acids, other organic acids, like lactic acids are also produced. Free O2, whenever available is also consumed by tapeworms. Rate of consumption is maximum in the anterior proglottids.

Excretory System:

Excretory system of T. solium consists of lateral longitudinal canal, secretory canals, capillaries and flame cells. Four main collecting canals traverse the entire length of the strobila. The two ventral canals remain ventra-laterally situated and two dorsal canals are dorsolateral. All these canals are situated in the peripharyngeal zone of the medullary parenchyma.

A single transverse canal connects the two ventral canals at the posterior end of each proglottid. The ventral vessel carries water away from the scolex, the dorsal vessels toward it. Within the scolex, all the four longitudinal canals may be joined by a network of canals forming nephridial plexus.

Along the length of ventral canals, a series of secondary tubules arise that may in give rise to tertiary tubules. All the free end of terminal tubules is flame cells. Usually the flame cells get arranged in groups of four. A flame cell is of irregular shape, with granular cytoplasm and nucleus.

The flame is actually a group of cilis that arise from a concave basal plate located near the cell nucleus. The cilis are enveloped in the funnel shaped enlargement of the free end of the tubule. Waste products collected through the flame cells are passed down the tubules into the main canals.


Term Paper # 6. Nervous System and Respiratory System of Taenia Solium:

Nervous System:

The nervous system consists of two ganglia in the scolex. The ganglia are connected by a broad transverse commissure.

Slender nerves are given off to each sucker and rostellum, and two lateral longitudinal nerve cords run the entire length of strobila.

Reproductive System:

A pair of male and a pair of female reproductive organs are found in each mature proglottid of the body. Therefore, each proglottid of the body is hermaphrodite.

A. Male Reproductive Organs:

1. Testes

2. Vasa efferentia

3. Vas deferens

4. Cirrus and cirrus sac

1. Testes:

The testes are numerous, small, around structures which are scattered in the anterior dorsal part of each proglottid. Their number in each proglottid may vary from 15 to 200.

2. Vasa Efferentia:

These are numerous minute ducts which arise from testes and collectively open into the vas deferens.

3. Vas Deferens:

It is a long coiled tube which arises from the middle of the segment and runs transversely either to the left or right to open into the genital strum.

4. Cirrus, Cirrus-Sac and Genital Atrium:

The distal end of vas deference forms a thick, muscular and eversible penis or cirrus. It is surrounded by a muscular pouch, the cirrus sac or cirrus sheath. Cirrus is covered with spines, bristles or hooks. It opens into a cup-shaped genital atrium by male genital pore. Genital atrium opens outside by common gonopore. The gonopore is situated on a tiny genital papilla in the middle of the lateral margin of proglottid. Common gonopores of successive proglottids lie alternately.

B. Female Reproductive System:

It includes the following parts:

1. Ovary

2. Oviduct

3. Ootype

4. Vagina

5. Uterus

6. Vitelline Glands

7. Mehlis’s Glands or Shell Glands.

1. Ovary:

A bilobed ovary is present in the posterior part of each proglottid. Each tube is a dorsoventrally flattened much branched structure. The two lobes are joined with each other by a transverse bridge called ovarian isthmus.

2. Oviduct:

The oviduct arises from the transverse ovarian isthmus. It is a short and wide tube which opens into the ootype.

3. Ootype:

It is a small round chamber which is situated at the junction of the oviduct and vitelline duct. Numerous unicellular shell glands or Mehlis’s glands are present all round it.

4. Uterus:

The uterus is a closed tube or sac-like structure which arises from the ootype and extends into the anterior parts of the proglottid. In gravid proglottid, the uterus is large and branched to fill the proglottid completely. It contains fertilized eggs and developing embryos.

5. Vagina:

The vagina arises from the receptaculum seminis or eminale receptacle in the form of narrow tube. The seminal receptacle is a short wide tube which is joined with the ootype on one side and on the other opens into the vagina.

6. Vitelline Gland:

It is a dense, bilobed structure formed of many follicles and is situated behind the ovary. A short vitelline duct arises from it and opens into the ootype. The fluid secreted by it contains much yolk which collects around the egg.

7. Shell Glands or Mehlis’s Glands:

There are innumerable, unicellular glands, which are situated around the ootype and poor their secretion in it.


Term Paper # 7. Life History of Taenia Solium:

The life-history of Taenia is complicated and digenetic, being completed in two hosts. The primary host is man and the secondary host is pig.

Fertilisation:

Self-fertilisation occurs as a rule. The cirrus of the segment is inserted into the vagina of the same segment. The sperms received are stored in the receptaculum seminis. The eggs are fertilized in the oviduct.

Copulation occurs only if gonopores of two mature proglottids come in contact due to folding of strobila. During copulation cirrus is inserted into the vagina and sperm are transferred.

Capsule Formation:

In ootype each fertilized egg or zygote becomes associated with a large yolk cell or vitelline cell secreted by the vitelline gland. The zygote and yolk cell are enclosed in a thin shell or chorionic membrane. It is formed by the material exuded by the yolk cell.

The capsulated eggs are collected in the uterus, where these undergo further development. Passage of capsules into uterus is lubricated by secretion of Mehlis glands. To accommodate developing embryos, the uterus becomes highly branched.

Eggs:

The eggs are very small measuring about 40 microns in diameter. These contain a large amount of yolk and each is surrounded by an egg shell or egg-capsule.

Development Cleavage, Heaxacanth and Onchosphere Formation:

Cleavage starts when the egg capsule is in the uterus (inside host’s intestine). The first division is unequal. It produces a large megamere and a small embryonic cell. The megamere divides again and again and thus many megameres are produced. The embryonic cell divides repeatedly and produces two types of cells—larger mesomeres, and smaller micromeres.

The micromeres form a ball of cells, the morula, in the centre. Mesomeres form an envelop around the morula. The megameres forms an outer covering around the mesomeres envelop. The megameres absorb yolk from the yolk-cell and supply nourishment to the developing embryo. The yolk-cell reduces in size, breaks and gradually disappears. The yolky megameres fuse to form the nutritive outer embryonic membrane. This too gradually disappears.

The middle mesomere layer forms a thick and hard shell or the embryophore or the inner embryonic membrane around the morula (micromeres). A basement membrane is also formed beneath the embryophore.

The morula forms the embryo proper. It develops three pairs of hooks and is known as a hexacanth embryo. The whole structure (hexacanth, embryophore and the egg-capsule) is known as an onchosphore.

But the time the onchosphere are formed the uterus in the gravid proglottid develops 7 to 13 branches on each side and fills the entire proglottid. The uterus contains 30,000 to 40,000 onchospheres.

Infection of Secondary Host:

The development of egg up to the formation of onchospheres takes place inside the host body. The gravid proglottids detach from the body of the parasite and come out along with the host faeces. These infect the secondary host when pig feeds upon the contaminated faeces. Dog, canals or monkeys are also infected sometimes and even auto-infection of man is also possible.

Formation of Cysticerus or Bladder Worm:

The onchosphere in the stomach of the secondary host loses the embryophore and basement membrane by the action of acidic juice. The larva now reaches intestine where the two remaining hexacanth membranes are dissolved by alkaline juice. The hexacanth now bores through the intestinal epithelium to reach the blood vessels with the help of hooks by which the larva anchors to the intestinal wall while the secretion of penetration glands dissolves the intestinal wall. This process takes about 10 minutes.

The books having served the purpose are died off. The hexacanth are now carried along the blood vessels to the liver via the hepatic portal vein from where it may reach the heart and through the arteries to the striated muscles of the tongue, shoulder, neck, thigh, heart etc. Here they settle down and develop into bladder worms or cysticercus. Sometimes they invade organs like lungs, liver, kidney or brain.

The formation of bladder worm form the hexacanth larva, which is devoid of hooks, takes about 10 weeks within the body of pig. During this process, the larva feeds on host tissue and grows to about 4.5 mm in length and 6 mm in width. By the breaking down of the central mass of cells of the larva, a central cavity is formed which is filled with the fluid mainly consisting of blood plasma of the host.

The larva at this stage is like a bladder and is lined with a thin wall consisting of outer thick cuticle and inner germinal layer. The wall of the bladder now thickness and invaginates at the anterior end. The invagination is now differentiated as inverted scolex, or proscolex possessing suckers, hooks and rostellum. The larva at this stage is known as bladder worm or cysticercus. As it is supposed to have a wall of cellulose it is also sometimes called cysticercus cellulosae.

Infection of the Primary Host (Man):

The pig flesh (or the park) infected with cysticerci is called “measly” pork due to its spotted appearance. Sometimes the cysticerci are so numerous that they occupy more than 50% of the total volume of a piece of flesh (numbering more than 500 per kilogram of pork).

When raw or imperfectly cooked pork containing cysticerci is eaten by man, the outer cyst well is digested off, the scolex evaginates, and the bladder disappears (or digested by the host’s digestive juices). The scolex attaches itself to the intestinal wall with the help of its suckers and hooks. The neck begins to produce proglottids by budding. The parasite becomes mature in about 2 to 3 months.

Pathogenesis or Effect on Host:

Disease caused by the infection of tapeworms is called cestodiasis. Infection may be due to the adult worm or by its cysticercus larva. The effects of infection accordingly are called taeniasis and cysticercosis.

1. Taeniasis:

It is infection of a person with adult worm. Usually one tapeworm is present in the intestine because presence of a tapeworm provides immunity (premonition) against fresh infection. Its presence produces a variety of symptoms in the host. This causes abdominal pain, nausea, anaemia, indigestion, increased appetite and increase in the number of eosinophils (eosinophilia). The effect of parasite on healthy host is not very serious but severe symptoms develop in children and weak patients.

2. Cysticercosis:

This is caused by infection with cysticercus larva or bladder-worm. The larva may get encysted in host’s voluntary muscles or, cardiac muscles in any part of the body including eyes, heart, spinal cord, brain etc. The symptoms may be epileptic fits, convulsions, giddiness, headache, vomiting, or local paralysis.

Treatment:

Anthelminthic drugs such as camoquin, carbon tetrachloride, aspidium, dichlorophen are used to treat tapeworm infection. Praziauantel (pyrazionis quinolines) is the modern drugs which kills the adult tapeworm as well as the cysticercus. Niclosamide kills the adult worm alone. Flubendaxole is the only drug that works on cysticercus.

Prophylaxis:

To avoid eating raw or imperfectly cooked pork is the best way of preventing infection. Pork bladder-worms are killed when heated to 55°C but the centre of large pieces of pork remains uncooked.


Term Paper # 8. Parasitic Adaptations of Taenia Solium:

Taenia is an intestinal parasite of vertebrates. It has undergone great structural modifications to meet the demands of its specific environment. Several complications have arisen in its life-history to ensure dispersal of race.

The modifications due to parasitic mode of life can be discussed under the following two heads:

I. Structural Modifications:

A. Changes in the External Form:

1. Body is dorsoventrally flattened and ribbon-like or tape-like.

2. The anterior end of the body or the head is modified into a holdfast or region of attachment. It has developed suckers and hooks to ensure that a firm holds of the host tissue.

3. Neck continuously develops new proglottids due to which animal grows in length throughout life.

4. Body or strobila consists of numerous immature, nature and gravid proglottids. Mature proglottids contain a complete set of male and female reproductive organs. Gravid segments possess only fertilized eggs and embryos, and possess power to detach.

B. Change in the Internal Organization:

1. The surface of epidermis around the body is lost and is replaced by a thick and resistant cuticle formed of insoluble proteins to protect it from the effect of intestinal juice of the host.

2. Absence of alimentary canal since Taenia ingests digested food by diffusion through the general body surface.

3. Excretory system takes the function of osmoregulation. It removes the excess water of the body which enters with the diffused digested food.

4. Respiration is anaerobic type since free oxygen is not available at the sites where parasite lives.

5. Nervous system is reduced and sense organs are totally absent.

6. Each proglottid is an independent individual because it contains a fully developed set of male and female reproductive organs. Fertilization is internal. A large number of eggs (30,000 to 40,000) develop from the ovary of each segment so that some of them may persist during transmission and further development.

7. Germarium (ovary) is highly branched to that it can produce large number of eggs.

II. Complications in the Life-History:

1. To cover the risk of finding individuals of different sexes in one host the organism and moreover each segment is hermaphrodite and there occurs self-fertilization.

2. These possess enormous fertility, the mature proglottid producing about 30 to 40 thousand eggs. The over­production of off-springs is necessary to maximize the chances of reaching the proper host and ensure the perpetuation of race.

3. The complicated life-history is a remarkable feature in the parasite since a secretory host; pig is introduced to ensure its dispersal from one primary host to another.

III. Physiological Adaptations:

1. Taenia stimulates the intestinal mucosa to secrete the mucous which forms a protective covering around the parasite to protect it from the intestinal juices.

2. Cuticular covering of the body also protects the parasite from the digestive juices.

3. Absorption of liquid food from the host.

4. Anaerobic respiration.

5. Osmoregulatory functions of excretory system.

6. Development of innumerable eggs by each proglottid and to accommodate them, the uterus in each gravid segment becomes distended, branched and other reproductive organs degenerate.

7. Life history is complicated involving two hosts-primary host (man) and secondary host (pig, catties, etc.). Onchospheres produced in millions enter the body of secondary host when it feeds the infected faeces of man.


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