Structure life cycle pathogenicity and control measure of Taenia solium

Structure

External morphology :

1. Shape size and colour:Taenia solium is usually opaque white in colour but cremes, yellowish or greenish colouration is also common.The body is 1 to 5 meters long, flattened like a ribbon or tape.The two flat surface represents the dorsal and ventral surfaces respectively,but from the external examination, it is not possible to identify them.Internal view reveals that surface closer to testes is dorsal and nearer surface.The elongated body is extremely narrow anteriorly and gradually broadens towards the posterior.

2. Segmentation: Elongated body of tapeworm is divided into a great number of parts or segments, called proglottids, possibly up to about 850 altogether.Segmentation of tapeworm is called pseudo-metamerism in contact to the true metamerism of annelid and arthropod.Therefore, the term 'segments 'in tapeworm is being used solely for convenience and in no way implies a true metameric segment. : Elongated body of tapeworm is divided into a great number of parts or segments, called proglottids, possibly up to about 850 altogether.Segmentation of tapeworm is called pseudo-metamerism in contact to the true metamerism of annelid and arthropod.Therefore, the term 'segments 'in tapeworm is being used solely for convenience and in no way implies a true metameric segment. The entire body is divided into three distinct parts:1) an anterior scolex or head, 2) a short unsegmented neck and 3) a segmented strobila.

3. Scolex: It represents the anterior end of the body .It is a knob like, biradially symmetrical and 0.6 to 1 mm wide.In en-face view appear roughly mobile cone, rostellum.It is armed with 22 to 32 curved chitinous hook, arranged in a two rows or circles are larger, each measuring 0.14 to 0.18mmand those of posterior circle are smaller each measuring 0.11 to 0.14 mm. Each hook consists of a base by which it is fixed, a blunt projection or handles directed towards the apex, and a conical outwardly directed blade. The broadest part of scolex bears for hemispherical highly muscular suctorial organ. the true suckers or acetabular, one at the each angle of the quadrangle, one at each angle of the quadrangle.Suckers are devoid of hooks or spines.

The scolex with the help of its hooks and sucker lies buried in the host's intestinal mucosa, providing firm adhesive to the body against the losing action of peristaltic movement of the host intestine. It is thus an organ of attachment or holdfast. The term "head " frequency used for the scolex is thus, inappropriate.

4.Neck: It is a well defined, short, narrow,and unsegmented region behind scolex. Unlike scolex, it is dorsoventrally flattened. It has been variously termed the budding Zone, growth Zone , area of proliferation and rate of segmentation because it is this reason where the segments or proglottids, constituting strobila, are budded.

5) Strobila: It forms the main bulk of the body. It consists of 800 to 1,000Rsegments or proglottids arranged in a linear series in a chain -like fashion . (The species sol, according to Leuckart has got its name from churches, a Syrian word referring to a chain). A proglottis is a unit part of the body enclosing a complete set of genitalia. Linear repetition of proglottis, and hence of genital organs, is termed proglottisation.Proglottids are budded off in the neck region and pushed backwards due to the addition of more proglottids in front.Thus, in a strobila , anterior proglottids are the youngest, while those at the posterior end are the oldest. Adjacent proglottids remain attached together by longitudinal muscles, excretory ducts and nerve cords, which extend along the entire body length. According to the degree of development, the strobila includes the three kinds of proglottids:immature, mature,and gravid. a) Immature proglottids : These comprise of about 200 anterior proglottids just behind the neck. They are youngest, sexually immature and devoid of the reproductive organ. They are short, broader than long and rectangular in outline.

b) Mature proglottids: There are about 450 mature proglottids forming the middle part of the strobila.These are large and squarish in outline. The anterior 100 to 150 proglottids.

contain only male reproductive organs, while the posterior 250 mature proglottids develop both male and female reproductive organ making them hermaphrodite .Each mature proglottid, on one side, bears a tiny protuberance,the genital papilla, at the tip of which is situated the common genital pore.These pore in the successive proglottids situated alternatively on right and left the side. A mature proglottid is a complete reproductive unit and produces eggs which are fertilized by its own sperms (self-reproduction) or by those of other mature proglottids ( cross-fertilization).

c) Ripe or gravid proglottids: The oldest and the last 150 to 350 proglottids, up the posterior and the body, then broad in outline. All the male and female reproductive organ have degenerated except the highly branched uterus full of fertilized eggs.

6: Apolysis: Small groups of gravid proglottids regularly detach from the posterior end of the strobila and pass out with the host's faeces.Shedding of gravid proglottids is termed as apolysis and the tapeworm exhibiting this phenomenon is called politician contrast to the analytic tapeworm (most pseudo phyllids ), which retain all their proglottids through life.Apolysis serves at two-fold purpose.1. It serves to transfer the developing embryos to the exterior, where they can be ingested by the secondary host, and 2. it limits the size of a body which may otherwise continue attain enormous length due to continued proliferated in the neck region.

Life cycle of Taenia solium

Copulation and fertilization:Self-fertilization occur by the insertion of the cirrus of one proglottid into the vagina, of same proglottids and sperm are deposited there. From the vagina,the sperm comes to lie in the seminal receptacle from where they fertilize the eggs in the oviduct. After copulation the sperm is stored temporarily in the seminal receptacles waiting for them maturity of the eggs and when such eggs are transformed into the capsule and packed in the uterus. Later the various reproductive organs degenerate and the uterus.become distended and branched heaving more then30000-40000 capsule.

Formation of egg capsule: After fertilization, the zygote gets surrounded by a yolk in the ootype received from the vitelline glands through the vitelline duct. The zygote and yolk then become enclosed in a thin shell.The structure, thus formed is called capsule which passes into,where further development takes place. The secretion of Mehlis's gland facilitates the passage of capsule in the uterus, it develops lateral branches to accommodate them. The gravid proglottid gets separated from the strobila and passes out with faeces of the host.

Development: It starts when the eggs enter the uterus. Cleavage of eggs cell is holoblastic and unequal. The unequal. The zygote first divides unequally to give rise a larger mega mere and a small embryonic cell. The megaere divided the number of times to give rise to several similar megamere. Similarly, the embryonic cell divides repeatedly to give rise to two types of cells, larger mesomeres, and smaller micromere.The three types of cells,i.e, larger megameres, medium sized Mesomeres, and smaller micrometre are resulted from zygote.In fact, the small micromeres from an inner ball of cells mass called morula.Themegemerefused to form the outer embryonic membrane which finally disappears. Themesomeresform the inner embryonic membrane which is hard, thick, cuticularized and striated. Below the embryo here , a thin basement membrane is also formed. The inner cell mass of morula forms an embryo develops six chitinous hooks at the posterior side. The six hooked embryo is called hexacanth, which possess a pair of pentagonal glands and is surrounded by two hexacanth membranes. The hexacanth embryo, hexacanth membranes, basement membrane embryo here, and the eggs shell or chorionic membrane together is known as oncosphere. The gravid proglottids which pass out from the host body contain embryos in oncospheres stage.

Transmission to secondary host:The discharged gravid proglottid are eaten up by pigs with human faeces. After reaching in the stomach of a pig, the capsule shell and other membranes around the hexacanth dissolve resulting in the liberation of hexacanth. The hexacanth now starts boring through the intestinal wall with the help of the pair of unicellular penetrating glands funds between the hooks The hooks help in anchoring it. The hexacanth enters the blood vessel of the intestine and passes through the heart and finally comes to lie in the striated muscle in any part of the body. They usually settle in the muscles, they lose their hooks, increasing in their size and acquire a fluid filled, central cavity then that become encysted in a circular covering to become cysticerci bladderworms.Thus, pig becomes infected.

Cysticercus or bladder worm: It is the larval stage of taenia which has been formed by the modification of hexacanth stage. It is a bladder-like sac filled with a clear watery fluid having mostly blood plasma of the host.The wall of the bladder consists of an outer cuticle and inner mesenchyme. The thickening arises gradually on one side of the bladder which marks the anterior end of the larva. The thickened area invaginates as a hollow knob which develops suckers on its inner surface and hooks are developed at its bottom. Now, this inverted knob is called proscolex which bears suckers, hooks,and rostellum.

Transmission to primary host: When the man, the primary host, ingest raw or improperly cooked pork containing cysticerci, the cysticerci become active in the intestine. Bladders are digested in the stomach of the host and the proscolex gets evaginated so that the suckers and rostellum come to lie on the outer surface as in the adult. Thus, a scolex and a small neck are formed. The scolex anchors itself to the mucous membrane of the intestine and the neck proliferates a series of proglottids to form the strobila. It takes nearly ten to twelve weeks for a proscolex to be converted into an adult Taenia, which starts producing gravid proglottids with oncospheres with 8 to 10 weeks.

Pathogenesis (symptoms)

Man fall a victim to adult tapeworm as well as its cysticerci; effects on the former are referred to as taeniasis and those of the latter as cysticercosis.

(a) Taeniasis: It is indicated by a variety of symptoms including in the abdomen, nausea, anaemia, increased appetite, increased of eosinophil cells in blood, and above all, nervous disorders of the type occurring in epilepsy. These serious disorders are caused by toxins produced by the parasite and not, as believed earlier, by its continued drain on the host's digested food. Hooks and suckers may cause mechanical irritation in , which may initiate reverse peristalsis leading to auto-infection.Usually,a single tapeworm is found to parasitize a host. This is because the presence of one tapeworm provides a kind of immunity or premunition to the host against fresh infection.

(b) Cysticercosis: It is far more dangerous than taeniasis. Encystment of bladders may take place in the host's voluntary muscles, cardiac muscles, and even in some more delicate vitals organs like liver, eyes and brain. Removal of cysticerci from these delicate tissues is extremely difficult. Cysticercosis of the brain results in several degenerative changes and necrosis in the brain and the patient show epileptic behaviour.

Treatment control/ prevention:

Infection of tapeworm can be tackled by Several anti- helminths drugs such as camo quin , carbon tetrachloride, oleoresin of male Aspidium (fern), quinacrine, antiphon , dichlorophen, etc.The most satisfactory compound for human infection is Yomesan (5-chloro N-; 2 chloro-4-nitrophenyl).Under the action of drugs, strobila is removed but the embedded scolex persists which again buds off a new strobila. Removal of scolex can be brought about by surgery.Removal of cysticerci,especially from dedicated organ like brain, eyes, and liver is extremely difficult.

Consumption of undercooked measly pork should be avoided .Faeces of infected, person should be properly disposed of and destroyed, preventing pigs having access to them and ingesting hexacanth embryos.

Reference:

Aggarwal Sarita. A Text Book of Biology. New Delhi.: Madhuban Educational Books, 2011.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L., Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

http://www.biologydiscussion.com/

http://www.parasitesinhumans.org/

https://web.stanford.edu/class/

https://en.m.wikipedia.org/wiki/Taenia_solium