Module Lecture of 2nd Year Introd + Helm in Tho Logy

8/3/2019 Module Lecture of 2nd Year Introd + Helm in Tho Logy

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INTRODUCTION TOMEDICAL

PARASITOLOGY By Dr. Eman D. El- Kerdany

Prof. of Medical Parasitology,


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INTERRELASHIONSHIPS BETWEENORGANISMS

Symbiosis ( living together) Though you may never have even heard of the

word symbiosis , it plays a huge part in the world you live in. The definition of symbiosis is a closeand often long term relationship between twodifferent biological species.


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THERE ARE THREE DIFFERENT TYPES OFSYMBIOSIS;

1-commensalism,2-mutualism,

3- and parasitism.


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COMMENSALISM

is the type of symbiosis in which oneof the organisms benefits from the

relationship, and the other one is notaffected.An example of commensalism isclownfish and anemone


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THE SECOND TYPE IS MUTUALISM

, in which both organisms benefit fromthe close relationship.

An example of mutualism is therelation between a butterfly or a beeand flowers or crocodiles and Egyptianteeth cleaning plovers]


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PARASITISM--

Lastly, the third type of symbiosis isparasitism, in which one organism benefits ,

however, the other is harmed .The benefiting partner is calledthe parasite and the other partner is called

the host . The parasite is dependent on thehost for food or shelter or bothFor example, intestinal parasites orectoparasites


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PARASITISM

Ectoparasites , that which live on the outersurface of the host (E.g: - ticks, mites,

leeches)


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Endoparasites, that which live inside the

body of the host (E.g: - tapeworm, liverfluke).Endoparasites are generally disease

causing. The disease causing parasites arecalled pathogenic parasites


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PARASITIC

In ancient Greece, the person gettingfree meals for entertaining others by hisamusing conversations was called aparasite - 'para' refers to beside and 'sitos'refers to grains. Thus, parasitism is defined

as an association between individuals of two different species in which one isbenefited and the other is harmed.


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1-Superinfection is reinfection with the same

species of parasite from external source, while

2- Auto infection is the case when an infectedperson reinfect himself by his own old infection.

This may be external or internal autoinfection. 3- Hyperinfection ; in immunosuppressed

individules. A type of internal autoinfection

TYPES OF PARASITISM.


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. Overall, however, symbiosis isvitally important to millions of our

world's most fascinating creature'ssurvival .


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Evaluation:

1. Define symbiosis, commensalism,mutualism, and parasitism.2. Give two examples of pairs of organismsthat have these symbiotic relationships:commensalism, mutualism, andparasitism and explain the relationship.


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PARASITOLOGY Parasitology is a biological

phenomenon concerned with The dependence of one living

organism on another . OR the study of the relationship

between a parasite and its host.

This is the topic in this course


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PARASITOLOGY

. This method of existence is the single mostsuccessful way of making a living, and it hasbeen estimated that no less than 80% of allspecies of organisms are parasites.(1992, Sci. Am. 267(4): 42-48; 1998, Int J

Parasitol 28(12): 1939-1941). It is likely that

this is an under-estimation.


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MEDICAL PARASITOLOGY

The subject which deals with

The parasites

1- Morphology2- Habitat3- Life cycle of theparasite

4- Its mode oftransmission

The infect man ( Host ),

5- The diseases produced by theparasite, clinical picture and theimmune response of the host .6- The various methods of the

diagnosis,7- The treatment8- The prevention and control


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TYPES OF PARASITES:

1. Obligatory parasite that cannot exist without ahost.

2. Facultative parasites that are able to existindependently of their host, leading a free livinglife.

3. Accidental or Incidental parasites that enteraccidentally and can live in a host different fromtheir normal definitive host

4. Opportunistic parasites are those of low pathogenicity and become highly pathogenic inpatients with a defective immune system.


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TYPES OF PARASITES

ACCORDING TO THEIR HABITAT

1- Endoparasites which live inside their hostcausing infection2-Ectoparasites which are found attached to theskin of their host or its superficial tissue causinginfestation ( Insects)


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TYPES OF HOSTS:

1. Definitive host in which the adult stage of theparasite lives, or sexual reproduction takes place .

2. Intermediate Host in which the immature or

larval stage of parasite is found, or in which theparasite multiple asexually. 3. Reservoir host: An animal which is utilized by a

parasite as a temporary refuge till it reaches itsappropriate definitive host is referred . It is

generally a animal which is normally infected witha parasite that can also infect man. For example,dogs and cats are reservoirs of Leishmania .


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4. PARATENIC HOST OR TRANSPORTHOST

Sometimes the parasite ( larval stage) enters ahost in which it does not undergo any development but remains alive till it gains entry in the definitive host or intermediate host. Such ahost is termed as paratenic or transport host or acarrier host. These hosts are important for the

completion of the life cycle of certain parasitesas they are believed to bridge the ecological gapbetween the intermediate and the definitivehost.


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TYPES OF HOSTS

5. Vector (usually arthropod) that transmitsparasites from one host to another.


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LIFE CYCLE

The life cycle :From the definitive host back tothe same or another definitive host.

When a parasite requires only one host tocompletes its life cycle then it is said to have adirect life cycle.

When two or more hosts are required tocomplete the life cycle this is called indirect lifecycle.


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FROM THE LIFE CYCLE YOU HAVE TO


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FROM THE LIFE CYCLE YOU HAVE TOKNOW:

Def. hostHabitatPortal of exit of eggs to where ??? Diagnostic stageIntermediate host (s)

Infective stageMode of infection : Portal of entry

Infective stage


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SOURCES OF PARASITICINFECTION OR INFESTATION

1. Soil: Contaminated soil with human excretacontaining eggs of the parasite.

2. Water: Contaminated water may carry protozoal cysts and cercaria of schistosomes

3. Food: Fresh water fish, infected meat or raw vegetables


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SOURCES OF PARASITIC INFECTION

4. Animals: .Domestic animals such as dogs andcats can be a source of parasitic infection to man

Zoonosis is the term given to the diseases of animals which are transmissible to man.


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Contact with dogs may transmit parasitic infection

( Zoonosis)


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SOURCES OF PARASITIC INFECTION ORINFESTATION

5. Infected persons: can be direct sources of infection to himself ( ? ) or to others.

6. Arthropods : Blood sucking arthropodstransmit blood and

tissue parasites.


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SOURCES

7. Iatrogenic: through contaminated syringes asin transfusion malaria, or amongst drug addicts.

8. Nosocomial: is a parasitic infection acquiredin hospital and was not present at the time of admission.

9. Placenta: Congenital infection 10. Milk: Transmammary


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PORTAL OF ENTRY INTO THE BODY

Parasites ( infective stage) enter the human body through different routes

1. Mouth is the most important portal of entry forcysts of intestinal protozoa, and eggs of helminths

2. Skin : Active skin penetration occurs from the soil,water or introduced through blood suckingarthropods

3. Respiratory tract: Airborn infection occurs. 4. Placenta 5. Genital tract by sexual intercourse.


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DEVELOPMENT OF INFECTION

Once the parasite entered the body of its host ,it migrates to its final habitat where it matures tothe adult stage.

The time taken from its entry until theappearance of the first signs and symptoms of the disease is known the clinical incubation

period.


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The prepatent or parasitologicalincubation period refers to the interval

between exposure to infection and theearliest demonstration of the parasitesor their products in faeces, blood,urine etc


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PORTAL OF EXIT

For the continuation of the life cycle , theparasite ( Diagnostic stage) must have a portal of exit from the host and this can occur viafaeces as eggs of most helminths and cysts of intestinal protozoaurine ,sputum,blood orgenital tract .


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PATHOGENESIS OF PARASITIC INFECTION

The ways in which damage may be produced inparasitic infections can occur through differentetiologies:

1. Mechanical : The parasite may obstruct anormal passage causing intestinal obstruction orbile duct obstruction or appendicitis.


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Mechanical obstruction by Fasciola worm in the bile duct


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Hydatid cyst in liver


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2. Traumatic : External damage occurs when the

parasite invades the skin as in scabies or myiasis. Internal damage occurs when the parasitesattach themselves by their buccal capsule to theintestinal mucosa producing ulcers.


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3. Toxic : Circulation of certain toxic by-products of parasites produces generalizedmanifestations.

4. Necrosis : Enzymes elaborated by the parasiteproduce necrosis of tissues.


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5- Allergic Manifestations : Allergic reactions occur withi nsect bites.


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PATHOGENESIS OF PARASITIC INFECTION

6. Stimulation of the host immune response : Parasiticantigens stimulate both a humoral and cellular immuneresponse provoking tissue reactions consisting of cellular proliferation and infiltration at the site of

parasites antigens, or deposition of circulating immunecomplexes in the tissues or fibrous capsulation 7. Cellular destruction : Destruction of red blood

corpuscles , reticuloendothelial cells and other tissue

cells . 8. Neoplastic Formation: Parasitic infections may

contribute to tumour formation.


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Cellular infiltration with macropghges in Leishmania infection


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a) Multiple mucosal polypsin the descending andsigmoid colon

b) Severe sigmoidpolyposis coalescing intoa mass


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A large malignant tumour in the bladder,.The bladder walls are calcified ,
http://www.medcyclopaedia.com/Home/library/glossaries/malignant.aspxhttp://www.medcyclopaedia.com/Home/library/glossaries/tumour.aspxhttp://www.medcyclopaedia.com/Home/library/glossaries/calcified.aspxhttp://www.medcyclopaedia.com/Home/library/glossaries/calcified.aspxhttp://www.medcyclopaedia.com/Home/library/glossaries/tumour.aspxhttp://www.medcyclopaedia.com/Home/library/glossaries/malignant.aspx


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DIAGNOSIS OF PARASITICINFECTIONS

Clinical diagnosis depends on the characteristicsigns and symptoms related to the parasiticinfection.

Laboratory diagnosis can be achieved by : A)Direct methods microscopical examination of

the excreta, blood, tissues or smears. Culture andanimal inoculations.


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DIAGNOSIS OF PARASITIC INFECTIONS

B) Indirect methods ( Serology) These methods depend on the detection of antigens or antibodies in the

patients serum .They are mainly resorted to when parasites arepresent in tissues, or in cases of closed chronic infection These methodsdepend on the detection of specific antigens or antibodies in patientsserum.

C) Molecular biological methods Recently molecular biology techniques were introduced as a

means of diagnosing parasitic infections. i) DNA Probes: The DNA hybridization probe technique is based

on the assumption that each organism possesses a unique nucleic acidsequence.

ii) Polymerase Chain Reaction (PCR) : The principle of thistechnique depends on the ability of replicating a single target piece of DNA of the parasite in the presence of polymerase enzyme.


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MEDICAL HELMINTHOLOGY(WORMS)

Helminths or parasitic worms are multi-cellular,bilaterally, symmetrical elongated, flat orrounded animals. Helminths which occur asparasites in man belong to two phyla:

I. Phylum Platyhelminths (Flat Worms)

II. Phylum Nematoda (Round Worms)


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TYPES OF HELMINTHS

Trematods Cestodes Nematodes


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I. PHYLUM PLATYHELMINTHS

The platyhelminths or flat worms aredorsoventrally flattened, leaf -like or ribbon-like.Their alimentary tract is rudimentary orcompletely absentand they have no body cavity.Most of them are hermaphrodites


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This phylum is divided into fourclasses of which only

Trematoda and Cestoidea include human parasites and of

medical importance.


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CLASS TREMATODA Trematodes are commonly known as flukes .

General Morphology Adults are leaf-like, pear-shaped or elongate worms,

covered externally by a cuticle which may be smooth, spiny ortuberculated.

All trematodes possess at least two suckers as organs of attachment on their cuticle.

Beneath the cuticle are three layers of muscle fibers andthe bulk of the body consists of a spongy tissue in which theinternal organs are embedded.

The digestive system of a trematode starts by the mouthopening, found at the bottom of the oral sucker. The mouthleads to a pharynx, then a short oesophagus which bifurcatesinto two long blind intestinal caeca.


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Morphology of trematodes


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MORPHOLOGY

Fasciola spp. &Heterophes hetrophes


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CLASS TREMATODA: MORPHOLOGY The excretory system starts by a definite number of excretory cells ( flam cells ) . Waste products pass from the cell to the excretory tubules, excretory duct then into an excretory bladder which

discharges its contents through a pore at the posterior end of the fluke.


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The nervous system is simple. Itconsists of a ring of nerve ganglia,

around the pharynx, from whichnerve fibres ramify. The reproductive system , in almost

all the parasitic trematodes arehermaphrodites except bilharzia

worms


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Nutrition and Respiration

Trematodes are essentially anaerobic they feed on blood,intestinal contents, biliary secretionsand tissue juices depending on theirhabitat.

LIFE CYCLE OF TREMATODES


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Flukes are called digenetic trematodesbecause they undergo two different

modes of reproduction: Sexual in the definitive host and Asexual in the intermediate host which

is a snail.( Imp.)


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IMPORTANT POINTS IN THE LIFE CYCLE

Parasitic trematodes utilize snails asintermediate hosts.

With the exception of bilharziaworms, all trematodes lay operculatedeggs which may pass out of thedefinitive host as mature egg i.e with afully developed embryo (miracidium )

or pass as immature eggs Egg of all trematode


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gg o a t e atodeare all operculated

ExceptSchistosoma eggs


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Miracidium


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In water ( V. imp), eggs hatchliberating the miracidia which are

attracted to their specific snail. After snail penetration, the miracidia

transform into sporocysts . They give a second generation of

sporocysts or rediae and cercariae


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CERCARIA ( INFECTIVE STAGE)

Cercariae leave the snail in batches of hundredsat a time, they are highly developed larval forms.A typical cercaria has a body and a tail. The

body resembles in its organization the adultfluke .

The tail of the cercariae may be simple

(leptocercous) . It may be forked at its end(furcocercous) or provided with a fin ormembrane (pleuro-lopho-cercous) .

.


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CERCARIA


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CERCARIA ( INFECTIVE STAGE)

Cercariae do not feed in water, they swim freely for few days after which they either1-Penetrate the skin of the definitive hostor2- Encyst in a second intermediate host or onwater vegetations ( Encysted metacercaria )


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AS EXAMPLES OF PARASITIC

TREMATODES, THE FOLLOWINGFLUKES WILL BE STUDIED:Liver flukes Fasciola hepatica and F. gigantica Intestinal flukesHeterophyes heterophyes Blood flukes

Schistosoma mansoni Schistosoma haematobium


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CESTODES


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CLASS CESTOIDEACESTODES OR TAPEWORMS

General morphology Adults are flat, ribbon like and segmented. Their length varies from few millimeters to

several meters The body is divided into head or scolex, neck

and several proglottids or segments. The chainof proglottids is called strobila.

The scolex is provided with bothria (i.e. grooves) or suckers as organs for attachment,with or without rostellum and hooks.

The neck is the region of growth.

Platyhelminthes: Trematodes


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Flat,

Ribbon like,segmented

Platyhelminthes: Trematodes

Cestodes

Class:CESTOIDEA

M j f


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Major features

They are Platyhelminthes.The body is divided into segments.

The body is differentiated intoscolex , neck and proglottids

(segments).Each group of segments is called

strobila

- No body cavity.


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-No gutEach segment has both male & female R O.( hermaphrodites )

Adults are all endoparasites

The embryo is called a hexacanth .They are divided into two orders:

Pseudophyllidea and Cyclophyllidea


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CLASS CESTOIDEA Nutrients are absorbed through their cuticle or

tegument which has also a protective function by secreting substances that inactivate the hostdigestive enzymes. ( imp)

Reproduction is by self fertilization in the samesegment or by cross fertilization between differentsegments.

The Excretory System consists of flame cells andcollecting ventral and dorsal tubules runninglaterally, emptying through a bladder in theterminal proglottid.

The Nervous System in the scolex,

CESTODES


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CESTODESPSEUDOPHYLLIDEA CYCLOPHYLLIDEA

e.g Diphyllobothrium latum e.g. Taenia spp Hymenolepis

nana

1- Scolex

SCOLEX


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SCOLEX

Top view to the rostellumshowing the raw of hooks


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PSEUDOPHYLLIDEA - CYCLOPHYLLIDEA3- Gravid segment: shape, uterus, disintegrated or detached


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PSEUDOPHYLLIDEA CYCLOPHYLLIDEA4- egg

Coracidium

Hexacanthus

embryo

5- Embryo


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* Habitat of Adult worms :Small intestine of the D. H( man or animal)

* Eggs ( or gravid segment) are passed in the faecesImmature Mature

Operculated Rounded, smallResemble those of trematode Hexacanthus embryo

( oncosphere)

PSEUDOPHYLLIDEA CYCLOPHYLLIDEA6- Life cycle

They must reach

water

LIFE CYCLE OF CESTODES


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LIFE CYCLE OF CESTODES

Adults are parasites of the small intestine of man oranimals . They require one or two intermediate hosts with the

exception of Hymenolepis nana which has one host onlyacting both as intermediate and definitive host . Gravid segments or eggs of cestodes are passed in the

faeces of their definitive hosts.

Cestodes that infect man belong to two ordersPseudophyllidea and Cyclophyllidea


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LIFE CYCLE

In the Pseudophyllidea , the eggs are immature andoperculated resembling those of trematodes. They mustreach fresh water to become embryonated, and thenhatch liberating the coracidium . These are ingested by

Cyclops, which is the first intermediate host anddevelop into first stage larvae, the procercoid larvae .When the cyclops is ingested by fish (the secondintermediate host) they develop into plerocercoid

larvae. Man and fish-eating mammals become infectedby eating imperfectly cooked fish containing theplerocercoid larva i.e. second larval stage.


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LIFE CYCLE

In the Cyclophyllidea , the eggs are mature when passedin the stools. After their ingestion by the intermediatehost, the hexacanth embryos or oncospheres areliberated from the egg shell, penetrate the intestinalwall by aid of the hooks and develop in various organsinto cystic larval stages e.g. cysticercus - cysticercoid -hydatid or coenurus cysts. When these larval stages are

ingested by the definitive hosts they develop into adultsin their small intestines.


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TAPEWORMS TO BE STUDIED ARE:


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TAPEWORMS TO BE STUDIED ARE:

Pseudophyllidean Tapeworms Diphyllobothrium latum

Spirometra mansoni. Cyclophyllidean Tapeworms

Taenia solium Taenia saginata

Echinococcus granulosus Hymenolepis nana Dipylidium caninum


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unsegmented,bilaterally symmetrical,elongate, cylindrical worms

with a body cavity a patent digestive tract.The sexes are separate.

Most nematodes are free living and some of themrepresent the commonest human parasites.

PHYLUM NEMATODA ARE

II. PHYLUM NEMATODA


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General Morphology The nematodes are cylindrical worms, tapering at both ends. The

body is covered by a cuticle made of scleroprotein designed to resist

the digestive juices and enzymes of the host. The cuticle may besmooth or marked with various thickenings or expansions. Within thebody cavity lie the digestive, reproductive and parts of the excretory and nervous systems of the nematode.

The digestive system is a patent tube starting with the mouthopening anteriorly and ending posteriorly by an anus in females and a

cloacal opening in males. The mouth leads to the oesophagus whichhas a chitnized lumen. Its shape and size are useful for theidentification of the nematode. The shape of the oesophagus may becylindrical or filariform , club shaped, double bulbed, rhabditiformand stichosome or cellular.


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A cuticle made of scleroprotein designed to resist thedigestive juices and enzymes of the host.The cuticle may be smooth or marked with variousthickenings or expansions. It is secreted by thehypodermis which is a protoplasmic syncitial layer,thickened into four longitudinal chords.

Between the chords and below the hypodermis is asingle layer of longitudinal muscle cells which linethe body cavity

GENERAL MORPHOLOGY


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GENERAL MORPHOLOGY

The nervous system consists of a nerve ring surrounding theoesophagus from which nerve trunks extend anteriorly,posteriorly and laterally. Some nematodes posses a pair of chemoreceptors situated on minute papillae behind the anuscalled phasmids, others lack such chemoreceptors.

The excretory system is composed of two laterallongitudinal canals connected by a transverse tube whichopens in the cervical region.

The reproductive system in both sexes consists of a seriesof long tubules coiled around the intestine.

Female worms may lay eggs (oviparous) or may give birth tolarvae (larviparous or viviparous).


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Strongyloides

hookworm

TrichinellaTrichuris

pinworm

NEMATODES


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NEMATODES

Nematodes can be classified according totheir habitat into

1- intestinal and tissue nematodes or 2- by the presence or absence of Phasmids .

LIFE CYCLE OF NEMATODES


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LIFE CYCLE OF NEMATODES

Adult worm may lay Eggs LarvaeInfection by:Ingestion of larvated eggsOrPenetration of the skin by infective larvae

LIFE CYCLE


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LIFE CYCLE

CLASS ADENOPHOREA(APHASMIDEA)


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(APHASMIDEA)

Nematodes in this subclass are devoid of phasmidsand caudal papillae. The anterior part of the body is usually very thin and contains the oesophaguswhich is of the stichosome type. Females possess asingle set of genitalia. Eggs when laid are usually with polar plugs.

The following are important members of thissubclass :

Trichuris trichiura Capillaria philippinensis Trichinella spiralis .

CLASS SECERNENTEA( PHASMIDEA)


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( PHASMIDEA)

These nematodes are provided with phasmids andcaudal papillae. Females have a double set of genitalia and the eggs laid are devoid of polar plugs.This subclass includes the majority of parasitic

nematodes. The important members include :- Ascaris lumbricoides Toxocara spp. Enterobius vemicularis Dracunculus medinensis Ancylostoma duodenale

Strongyloides stercolaris

Module Lecture of 2nd Year Introd + Helm in Tho Logy

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