subkingdom metazoa 2

8/3/2019 Subkingdom Metazoa 2

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22-- Subkingdom MetazoaSubkingdom Metazoa

Phylum Platyhelminthes:Phylum Platyhelminthes:

This phylum contains the helminthes of lowest organization. TheThis phylum contains the helminthes of lowest organization. The

great majority of them are flattened from the dorsal to the ventral side,great majority of them are flattened from the dorsal to the ventral side,

hence the common name flatworm. Unlike nearly all other manyhence the common name flatworm. Unlike nearly all other many--

celled animals they have no body no cavity (acoelomate) the organscelled animals they have no body no cavity (acoelomate) the organs

being embedded in a sort of spongy "parenchyma" or packing tissue.being embedded in a sort of spongy "parenchyma" or packing tissue.

Because they have three wellBecause they have three well--defined germ layers, they are termeddefined germ layers, they are termed

triploblastic.triploblastic.


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Characteristics of phylumCharacteristics of phylum

Platyelminthes:Platyelminthes:11-- The members of the phylum either freeThe members of the phylum either free--living or parasitic,living or parasitic,

triploblastic acoelomatetriploblastic acoelomate animals, i.e. they posses no coelom.animals, i.e. they posses no coelom.

22-- They have soft dorsoThey have soft dorso--ventrally flattened andventrally flattened and bilaterally symmetricalbilaterally symmetrical

bodies, i.e. only one median or sagittal section can divide the bodybodies, i.e. only one median or sagittal section can divide the body

into two symmetrical halves, definite polarity of on anterior andinto two symmetrical halves, definite polarity of on anterior and

posterior ends.posterior ends.

33-- The body muscles are fairly well developed ofThe body muscles are fairly well developed of circularcircular andand

longitudinallongitudinal fibers, and share in the formation of the body wall.fibers, and share in the formation of the body wall.

44-- The digestive tract in its simplest from when present consists of a sacThe digestive tract in its simplest from when present consists of a sac

or a tube provided with a mouth and without anus.or a tube provided with a mouth and without anus.


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55-- The nervous system is very simple, and consist of a pair ofThe nervous system is very simple, and consist of a pair of

primitive ganglia whish serve as a brain are located in the anteriorprimitive ganglia whish serve as a brain are located in the anterior

of the worm. With longitudinal nerve cords and connected withof the worm. With longitudinal nerve cords and connected withtransverse nerves.transverse nerves.

66-- The excretory system is essentially formed of basic untles, knownThe excretory system is essentially formed of basic untles, known

asas "flame cells", (protonephridia)"flame cells", (protonephridia) soso--called from the flame likecalled from the flame like

fickering of a brush of cilia which keeps up a flow of fluid towardfickering of a brush of cilia which keeps up a flow of fluid toward

the larger branches or tubes, and ultimately to the excretory pore.the larger branches or tubes, and ultimately to the excretory pore.

77-- The haveThe have no respiratory, circulatoryno respiratory, circulatory ororskeletalskeletal systems.systems.

88-- All but a few of Platyhelminthes are hermaphroditic, as containingAll but a few of Platyhelminthes are hermaphroditic, as containing

complete male and female systems in each individual; incomplete male and female systems in each individual; in

tapeworms both systems are usually complete in each segment.tapeworms both systems are usually complete in each segment.

In addition to the ordinary sexual reproduction of the adults, manyIn addition to the ordinary sexual reproduction of the adults, many

flukes and tapeworms have special asexual methods offlukes and tapeworms have special asexual methods of

multiplication in the course of their life cycles.multiplication in the course of their life cycles.


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Classification of PlatyhelminthesClassification of Platyhelminthes

Phylum: Platyhelminthes is divided into fivePhylum: Platyhelminthes is divided into fiveclasses.classes.

11-- Class: TurbellariaClass: Turbellaria

Turbellarians are mostly freeTurbellarians are mostly free--living, creeping worms that combineliving, creeping worms that combine

muscular with ciliary movement to a chive locomotion. Unlike othermuscular with ciliary movement to a chive locomotion. Unlike other

platyplaty--helminthes classes, they have simple life cycle.helminthes classes, they have simple life cycle.

22-- Class: Monogenea (Monogenetic flukes)Class: Monogenea (Monogenetic flukes)Monoecious flukes, development direct with single host andMonoecious flukes, development direct with single host and

usually with freeusually with free--swimming, ciliated larva. All parasitic, mostly onswimming, ciliated larva. All parasitic, mostly on

skin or gills of fish.skin or gills of fish.


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33-- Class: Digenea (digenetic flukes)Class: Digenea (digenetic flukes)

Mostly monoecious, development inMostly monoecious, development in--direct, with first host adirect, with first host amollusk, final host usually a vertebrate. Mostly endoparasitic in allmollusk, final host usually a vertebrate. Mostly endoparasitic in all

classes of vertebrates.classes of vertebrates.

44-- Class: AspidogastreaClass: Aspidogastrea

55-- Class: Cestoda (tapeworms)Class: Cestoda (tapeworms)

Body usually divided into series of proglottids, no digestive organs.Body usually divided into series of proglottids, no digestive organs.

Usually monoecious. Development inUsually monoecious. Development in--direct with two or more hosts,direct with two or more hosts,first host may be vertebrate or invertebrate. Parasitic in digestivefirst host may be vertebrate or invertebrate. Parasitic in digestive

tract of all classes of vertebrates.tract of all classes of vertebrates.


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Structure of a generalized trematodeStructure of a generalized trematode

(Source: Introduction to(Source: Introduction toparasitology:parasitology: 19611961))


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Life cycle of a digenetic flukeLife cycle of a digenetic fluke

))19781978(Source: General Zoology"(Source: General Zoology"


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Economic importance ofEconomic importance of

platyhelminthesplatyhelminthesMembers of class Turbellaria are mainly freeMembers of class Turbellaria are mainly free--living, non parasiticliving, non parasitic

formsforms which have no significant role in agricultural production. Meanwhich have no significant role in agricultural production. Mean

while, members of the other classes are considerably animalwhile, members of the other classes are considerably animal

parasites. Class Monogenea individuals are distinguished as fishparasites. Class Monogenea individuals are distinguished as fish

parasites, mostly ectoparasites, mostly ecto--parasites on fish skin and gills.parasites on fish skin and gills.

Some are endoSome are endo--parasites in fish intestine or even in lumen andparasites in fish intestine or even in lumen and

bladder of members of some vertebrates. Class Digenea possessbladder of members of some vertebrates. Class Digenea possess

endoendo--parasites in liver, lung, blood vessels or intestine of birds andparasites in liver, lung, blood vessels or intestine of birds and

mammals. Members of class Cestoda are mostly parasites in intestinemammals. Members of class Cestoda are mostly parasites in intestine

of man and domestic mammals which also act as intermediate hosts.of man and domestic mammals which also act as intermediate hosts.


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Ex.Ex. 11--Liver Flukes:Liver Flukes:

There are two common species of liver flukes,There are two common species of liver flukes, Fasciola giganticaFasciola gigantica

andand Fasciola hepaticaFasciola hepatica of Fam.: Fasciolidae; class: Digenea. Bothof Fam.: Fasciolidae; class: Digenea. Both

Flukes are fairly similar, yet they can be distinguished by certainFlukes are fairly similar, yet they can be distinguished by certain

morphological anatomical characteristics. In many parts ofAfrica andmorphological anatomical characteristics. In many parts ofAfrica and

AsiaAsia F. giganticaF. gigantica is more common, whileis more common, while F. hepaticaF. hepatica is moreis more

common in Europe and Australia. In Egyptcommon in Europe and Australia. In Egypt F. giganticaF. gigantica is a veryis a very

common parasite of sheep, goats and cattle. The fluke is mostcommon parasite of sheep, goats and cattle. The fluke is most

prevalent in the northern parts of the Nile Delta.prevalent in the northern parts of the Nile Delta.


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Symptoms ofSymptoms ofFasciola giganticaFasciola gigantica

infection:infection:The liver fluke affects the definitive hosts, as during migration ofThe liver fluke affects the definitive hosts, as during migration ofthe young flukes from the intestine to the live, they producethe young flukes from the intestine to the live, they produce

hemorrhages in the intestinal wall and the liver capsule. Also, thehemorrhages in the intestinal wall and the liver capsule. Also, the

presence of the flukes and their eggs in the liver usually inducespresence of the flukes and their eggs in the liver usually inducesdevelopment of fibrous tissues replacing the liver cells. Mechanicaldevelopment of fibrous tissues replacing the liver cells. Mechanical

damage resulted due to the presence of large numbers of the flukesdamage resulted due to the presence of large numbers of the flukes

in bile passages. The infected animals usually become anemic duein bile passages. The infected animals usually become anemic due

to the toxic substance produced by the flukes. Jaundice is ato the toxic substance produced by the flukes. Jaundice is a

common appearance of the infected animals.common appearance of the infected animals.

The loss in animals infected with the live flukes is not only due toThe loss in animals infected with the live flukes is not only due to

the destruction of infected livers in slaughterthe destruction of infected livers in slaughter--houses, but also to thehouses, but also to the

reduction in the reproductively of the diseased animals.reduction in the reproductively of the diseased animals.


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The disease weakens the animals, thus devaluating them as aThe disease weakens the animals, thus devaluating them as a

source of meat, reduces their production of milk, decreased theirsource of meat, reduces their production of milk, decreased their

working and breeding activities, and may lead, in severe cases, toworking and breeding activities, and may lead, in severe cases, toserious fatalities in the farm livestock.serious fatalities in the farm livestock.

Life cycle of Fasciola gigantica:Life cycle of Fasciola gigantica:Eggs of the flukes leave the host body by traveling with bileEggs of the flukes leave the host body by traveling with bile

secretions to reach its small intestine, then along the large intestine tosecretions to reach its small intestine, then along the large intestine toleave the host body together with feces. In suitable externalleave the host body together with feces. In suitable external

environmental conditions a fully developed embryo, known as theenvironmental conditions a fully developed embryo, known as the

miracidium, is formed inside the egg in about two weeks. The eggsmiracidium, is formed inside the egg in about two weeks. The eggs

then hatch and a ciliated freethen hatch and a ciliated free--living miracidium is liberatedliving miracidium is liberated

environment is relatively short, being aboutenvironment is relatively short, being about 2424 hours. During thishours. During this

period the miracidium swims for an intermediate host which is theperiod the miracidium swims for an intermediate host which is the

snail, Limnaea caillaudi. Once the miracidium penetrates the snails'snail, Limnaea caillaudi. Once the miracidium penetrates the snails'

tissues it loses the ciliary covering and develops to the next larvaltissues it loses the ciliary covering and develops to the next larval

stage known as sporocyst.stage known as sporocyst.


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After a while, the sporocysts leave the original site of penetrationAfter a while, the sporocysts leave the original site of penetration

and migrate towards the digestive gland of the snail. Germ cells of theand migrate towards the digestive gland of the snail. Germ cells of the

sporocysts divide parthenogenically to give the next. Larval stagesporocysts divide parthenogenically to give the next. Larval stage

which is called the redia. In each sporocyst aboutwhich is called the redia. In each sporocyst about 88 rediae arerediae are

produced. Inside the body of redia there are clusters of germ cellsproduced. Inside the body of redia there are clusters of germ cells

which may divide parthenogenically to give a second generation ofwhich may divide parthenogenically to give a second generation of

rediae known as daughter rediae, which leave the body of the motherrediae known as daughter rediae, which leave the body of the motherrediae through a lateral pore situated anteriorly known as the birthrediae through a lateral pore situated anteriorly known as the birth

pore. Then, the germ cells in either the mother or daughter radia dividepore. Then, the germ cells in either the mother or daughter radia divide

parthenogencally producing the next larval stage known as theparthenogencally producing the next larval stage known as the

cercaria. The cercaria has a disccercaria. The cercaria has a disc--shaped body and a long simple tail.shaped body and a long simple tail.

The cercariae leave the body of the redia through the birth bore andThe cercariae leave the body of the redia through the birth bore and

leave out of the snail's body to the surrounding water. Emergence ofleave out of the snail's body to the surrounding water. Emergence of

the cercariae from infected snails usually startsthe cercariae from infected snails usually starts 55--66 weeks after theweeks after the

miracidium penetration.miracidium penetration.


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Then, the released cercariae swim and encyst on water vegetationThen, the released cercariae swim and encyst on water vegetation

given the metacercaria. The latter are the infective stage of the livergiven the metacercaria. The latter are the infective stage of the liver

fluke which remain viable for several months. When the final hostsfluke which remain viable for several months. When the final hosts

(cattle, sheep; goats) eat aquatic vegetation infestedwith the(cattle, sheep; goats) eat aquatic vegetation infestedwith the

metacercariae they lose their cysts by the host's digestive enzymes.metacercariae they lose their cysts by the host's digestive enzymes.

The release young flukes normally reach the liver by burrowing throughThe release young flukes normally reach the liver by burrowing through

into the abdominal cavity and entering from the surface, butinto the abdominal cavity and entering from the surface, but

occasionally they get into the circulation and may be distributed tooccasionally they get into the circulation and may be distributed to

abnormal locations. The flukes bore into the liver parenchyma on theabnormal locations. The flukes bore into the liver parenchyma on the

second to six day after infection but do not enter the bile passages untilsecond to six day after infection but do not enter the bile passages until

the seventh or eight week. The flukes live mainly on blood and becomethe seventh or eight week. The flukes live mainly on blood and become

mature in aboutmature in about 1010 weeks. Egg production begins in aboutweeks. Egg production begins in about 33 monthsmonths

and lasts several years. The fluke is capable of producingand lasts several years. The fluke is capable of producing 33..000000 eggseggs

per day and this may continue for aboutper day and this may continue for about 88--1111 years.years.


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Treatment and Prevention:Treatment and Prevention:

11-- Using effective chemical therapy to infected animals gives godUsing effective chemical therapy to infected animals gives godresults for eliminating the disease.results for eliminating the disease.

22-- Destruction of the snails that serve as intermediate hosts.Destruction of the snails that serve as intermediate hosts.

33-- Isolation of the infected animals in clean and dry pens.Isolation of the infected animals in clean and dry pens.

44-- Introducing clean and disinfested foods to the animals.Introducing clean and disinfested foods to the animals.

55-- Preventing animals of drinking or feeding on aquatic vegetationsPreventing animals of drinking or feeding on aquatic vegetationsgrown on river's or canal's banks.grown on river's or canal's banks.

Ex.Ex. 22-- Blood flukes: (Schistosomes)Blood flukes: (Schistosomes)These flukes live in blood vessels of certain vertebrates includingThese flukes live in blood vessels of certain vertebrates including

birds and mammals. They are dioeceous as both males andbirds and mammals. They are dioeceous as both males and

females are found separate. Schistsomiases or bilharziasis are thefemales are found separate. Schistsomiases or bilharziasis are the

common name of the disease induced by the blood flukes.common name of the disease induced by the blood flukes.


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Man and his domestic animals are severely affected by severalMan and his domestic animals are severely affected by several

species of schistsomes. Three species are mainly reported for man:species of schistsomes. Three species are mainly reported for man:

Schistosoma haematobium, S. mansoniSchistosoma haematobium, S. mansoni,, andand S. japonicum.S. japonicum. In EgyptIn Egypt

the earlier two species are present, while the last one occurs only inthe earlier two species are present, while the last one occurs only in

some countries of South East Asia.some countries of South East Asia. S. hoematobiumS. hoematobium induces urinaryinduces urinary

schistosomisiasis, where the worms are usually located in the pelvicschistosomisiasis, where the worms are usually located in the pelvic

vesicle venous plexus and its eggs are passed out in urine.vesicle venous plexus and its eggs are passed out in urine. S.S.

mansonimansoni, and, and S. japonicumS. japonicum induce intestinal schistosomisiasis. Adultsinduce intestinal schistosomisiasis. Adults

of both species are usually found in the mesenteric veins, and theof both species are usually found in the mesenteric veins, and the

eggs are voided in the feces of host.eggs are voided in the feces of host.

ManyMany SchistosomaSchistosoma species are reported in domestic animals.species are reported in domestic animals.

Schistosoma bovisSchistosoma bovis is the most common species infects cattle, sheepis the most common species infects cattle, sheep

and goats. Parasitic behaviour of such species resembles that ofand goats. Parasitic behaviour of such species resembles that of S.S.

mansoni.mansoni.


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Symptoms of schistosomias causedSymptoms of schistosomias caused

bybyS. bovisS. bovis in cattle:in cattle:

11.. Excretion of blood and mucus in the feces accompanied byExcretion of blood and mucus in the feces accompanied by

diarrhea, abdominal pain, and enlargement of liver and spleen.diarrhea, abdominal pain, and enlargement of liver and spleen.

22.. Irritation in intestinal walls due to infection leads to losing appetiteIrritation in intestinal walls due to infection leads to losing appetite

and anemic disorder.and anemic disorder.

33.. The infected animals lose vitality and become exhausted.The infected animals lose vitality and become exhausted.

44.. Blocking of small blood vessels due to the existence of wormsBlocking of small blood vessels due to the existence of worms

and eggs.and eggs.


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Life cycle ofLife cycle ofS. bovis:S. bovis:

The females ofThe females of S. bovisS. bovis lays eggs in the small branches of thelays eggs in the small branches of themesenteric veins. The eggs then make their way through the vesselsmesenteric veins. The eggs then make their way through the vessels

and mucosa of the intestine and finally into the lumen along withand mucosa of the intestine and finally into the lumen along with

formed stage, the miracidium which resembles that of liver fluke, exceptformed stage, the miracidium which resembles that of liver fluke, except

it is smaller and lacks the eyeit is smaller and lacks the eye--spots. The miracidia have a short lifespots. The miracidia have a short life

span in water (span in water (2424--3636 hours) and they die if they do not find the properhours) and they die if they do not find the proper

intermediate snail, which is usuallyintermediate snail, which is usually Bulinus contotus.Bulinus contotus.

The miracidia swim and penetrate into the snail tissues. Then, theyThe miracidia swim and penetrate into the snail tissues. Then, they

lose their cilia and transferred to sporocysts. Daughter sporocysts arelose their cilia and transferred to sporocysts. Daughter sporocysts are

also formed as in case of liver fluked. The germ cells inside thealso formed as in case of liver fluked. The germ cells inside thedaughter sorocysts divide repeatedly to give the next larval stage, thedaughter sorocysts divide repeatedly to give the next larval stage, the

cercariae. The cercariae leave the sporocysts and then the snail to thecercariae. The cercariae leave the sporocysts and then the snail to the

surrounding water. The cercaria has a pearsurrounding water. The cercaria has a pear--shaped body and a longshaped body and a long

forked tail and the whole body is covered with minute spines.forked tail and the whole body is covered with minute spines.


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The cercariae swim in water and live aboutThe cercariae swim in water and live about 4848 hours before findinghours before finding

the final host after they die in the absence of the host. When they findthe final host after they die in the absence of the host. When they find

the suitable host in the proper time, they penetrate the host's skinthe suitable host in the proper time, they penetrate the host's skin

goining inside the body leaving their tails outside. They young flukesgoining inside the body leaving their tails outside. They young flukes

are then migrated to the lymphatic or peripheral blood vessels alongare then migrated to the lymphatic or peripheral blood vessels along

to the heart and then to the lungs. Then, the flukes migrate to the liverto the heart and then to the lungs. Then, the flukes migrate to the liver

where they enter the blood vessels of the portal system. Thewhere they enter the blood vessels of the portal system. The

developing flukes eventually reach sexual maturity indeveloping flukes eventually reach sexual maturity in 44--55 weeks andweeks and

them leave the liver after coupling occurs. The coupled worms travelthem leave the liver after coupling occurs. The coupled worms travel

against the blood stream until they reach the mesenteric veins. Theagainst the blood stream until they reach the mesenteric veins. The

period between cercarial penetration and the appearance of eggs inperiod between cercarial penetration and the appearance of eggs in

feces is aboutfeces is about 5050--6060 days.days.


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Treatment and PreventionTreatment and Prevention::

11-- Chemical and mechanical destruction of the intermediate hosts.Chemical and mechanical destruction of the intermediate hosts.

22-- It is necessary to prevent the host animals from drinking andIt is necessary to prevent the host animals from drinking and

swimming in canals.swimming in canals.

33-- Isolation of the infected animals and introduce proper mediationIsolation of the infected animals and introduce proper mediation

to them.to them.

44-- Raising and keeping the animals in clean pens.Raising and keeping the animals in clean pens.


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A,A, different species ofdifferent species ofschistosomaschistosoma

11-- SchistosomaSchistosoma mansonimansoni

22-- SchistosomaSchistosoma haematobiumhaematobium

33-- SchistosomaSchistosoma japonicumjaponicum

These species that infected man wellThese species that infected man well

studg the lifecycleofstudg the lifecycleofschistosomaschistosoma bovis thatbovis that

infectedcows.infectedcows.


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generalizedgeneralizedB,B,Life cycle of schistosoma spp.Life cycle of schistosoma spp.

(Adapted from text book(Adapted from text book))19811981of zoology,of zoology,


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Ex.Ex. 33-- Tapeworms (The Cestoda):Tapeworms (The Cestoda):

Several species of the tapeworms have described. However, theSeveral species of the tapeworms have described. However, the

beef tapeworm, Taenia saginata and the pork tapeworm,beef tapeworm, Taenia saginata and the pork tapeworm, TaeniaTaenia

soliumsolium are commonly known all over the world. Cattle and pigs areare commonly known all over the world. Cattle and pigs are

the intermediate hosts ofthe intermediate hosts of T. saginataT. saginata andand T. soliumT. solium, respectively., respectively.

There are slight morphological differences between the two species.There are slight morphological differences between the two species.

The first species is longer than the later, and they are normally foundThe first species is longer than the later, and they are normally found

in the middle third of the intestine of man, whereas, the bladder wormin the middle third of the intestine of man, whereas, the bladder worm

or cysticercus localized in the muscles of the heart, diaphragm,or cysticercus localized in the muscles of the heart, diaphragm,

shoulder, tongue, etc. life cycle of both species is quite similar.shoulder, tongue, etc. life cycle of both species is quite similar.


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Symptoms ofSymptoms ofT. saginataT. saginata andand

infection:infection:

aa-- in the intermediated host:in the intermediated host:

11.. The presence of the cysticerci in the muscles of the intermediateThe presence of the cysticerci in the muscles of the intermediate

hosts in large numbers becomes harmful specially when present inhosts in large numbers becomes harmful specially when present in

vital organs like heart and brain.vital organs like heart and brain.

22.. The intermediate host animals have exhausted appearance.The intermediate host animals have exhausted appearance.

33.. When the eggs of the worms are ingested by man, they can developWhen the eggs of the worms are ingested by man, they can develop

into cysticerci.into cysticerci.


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bb-- In the final host:In the final host:

11-- The adult worm has large size that occupies of the human intestine.The adult worm has large size that occupies of the human intestine.

Accordingly the digestive and absorptive processes becomeAccordingly the digestive and absorptive processes become

disturbed.disturbed.

22-- The worm consumes large amount of the digested food found inThe worm consumes large amount of the digested food found in

intestine of the host leading to weakness and losing weight.intestine of the host leading to weakness and losing weight.

33-- The worm excrete poisonous metabolites which may be absorbed inThe worm excrete poisonous metabolites which may be absorbed in

the blood and cause cetain systemic complications.the blood and cause cetain systemic complications.


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Life cycle ofLife cycle ofTaeniaTaenia sp:sp:Taeina solium or T. saginataTaeina solium or T. saginata related to: Fam. Taeniidae;related to: Fam. Taeniidae;

order, Cyclopyliidae, class, Cestoda.order, Cyclopyliidae, class, Cestoda.

The infected man with a pork or beef (according to parasiteThe infected man with a pork or beef (according to parasite

species) tapeworm expels ripe segments, singly or in shortspecies) tapeworm expels ripe segments, singly or in short

chains almost every day each segment contains aboutchains almost every day each segment contains about 100100..0000

eggs. These eggs break out when the segments (proglottids)eggs. These eggs break out when the segments (proglottids)

disintegrate.disintegrate.


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The eggs are spherical and have a thin transparentThe eggs are spherical and have a thin transparent

outer envelope and a thick lamellated shell know as theouter envelope and a thick lamellated shell know as the

embryo pore. Within this shell there is an oncosphereembryo pore. Within this shell there is an oncosphere

(hexacanth embryo) which has six delicate lancet(hexacanth embryo) which has six delicate lancet--shappedshapped

hooklets.hooklets.

When the eggs are ingested by a suitable animalWhen the eggs are ingested by a suitable animal

(normally, cattle, pork), the oncospheres are liberated bore(normally, cattle, pork), the oncospheres are liberated bore

through the intestinal wall, and make their way, via blood orthrough the intestinal wall, and make their way, via blood or

lymph channels, usually to the muscles or meat. Theylymph channels, usually to the muscles or meat. Theyespecially favor the tongue, neck heat, and shoulder muscles.especially favor the tongue, neck heat, and shoulder muscles.

Having arrived at their destination they grow into bladderHaving arrived at their destination they grow into bladder

worms or cysticerci namedworms or cysticerci named Cysticercus cellulosaeCysticercus cellulosae..


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The cysticercus has a small head like that of the adultThe cysticercus has a small head like that of the adult

worm ivaginated into a fluidworm ivaginated into a fluid--filled bladder. Pork containingfilled bladder. Pork containingtheses larvae is called measly pork or measly beef.theses larvae is called measly pork or measly beef.

When cysticerci in pork are eaten by man, their wallsWhen cysticerci in pork are eaten by man, their walls

are digested in the stomach, and the liberated larvaeare digested in the stomach, and the liberated larvae

pass to the duodenum where the scloex are evaginatedpass to the duodenum where the scloex are evaginated

and the bladders disintegrate. The larvae then migrate toand the bladders disintegrate. The larvae then migrate to

the middle third of the intestine, the scloex of each larvathe middle third of the intestine, the scloex of each larvagets hold of the intestinal wall and start to grow togets hold of the intestinal wall and start to grow to

maturity in aboutmaturity in about 22 oror 33 months.months.


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Treatment and Prevention:Treatment and Prevention:

11.. Chemical treatment by using drugs that expel theChemical treatment by using drugs that expel thetapeworms from the final host.tapeworms from the final host.

22.. Destruction of the measly meat in the slaughterhouses.Destruction of the measly meat in the slaughterhouses.

33.. Prevention of eating raw or imperfectly cooked beef or pork.Prevention of eating raw or imperfectly cooked beef or pork.

..// 2011/2012

subkingdom metazoa 2

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