Medical partgfttggyytasitology lec 1.pdf

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Introduction to Medical
parasitology
1
st
. Lecture …..( 1 )
Mrs. Wasan Mohammed
Duhok Polytechnic University
Shekhan technical and medical college
Department of Public health
2023/ 2024

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Parasitology:-
IsthebranchofBiologicalsciencewhichmainly
dealswithalltheparasitesanditsinfectious
diseases.Wholeparasitologycoversmainlyparasites,
host and its association between them.
Introduction to Parasitology

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Isthebranchofmedicalsciencesdealingwithorganisms(parasites)
whichlivetemporarilyorpermanently,onorwithinthehumanbody
(host).otherparasiticorganismssuchasparasiticbacteria,viruses,fungi
andinsectsarenotinvolvedeveniftheyliveparasiticallybecausethey
havetheirconcernedsciences(bacteriology,virology,mycologyand
entomology)
Medical Parasitology

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►Parasite
► Is a living organism that lives in (endoparasite) or on
(ectoparasite) another organism, termed its host. It obtains
nourishment and protection while offering no benefit in return.
►Consequently, the host suffers from various diseases, infections,
and discomforts.
► However, in some cases, the host may show no signs at all of
infection by the parasite(asymptomatic).

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►According to the nature of the host-parasite interactions and the
environmental factors, parasites classified according to the following
criteria:
1.Ectoparasites (external parasites):are found on the external surface
of their hosts as in the presence of human lice on skin, ticks and mites.
2.Endoparasites (internal parasites):are found in viscera , coeloma ,
muscles of their hosts such as in tapeworms found in small intestine
and some protozoa like Entamoeba histoltyica.
1-Types of Parasites according to their
presence within or on the hosts

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1.An obligatory parasite :-that is completely dependent on its host
and can’t
2.survive without it e.g. hookworms and Entamoeba histolytica .
3. A facultative parasite:- that can change its life style between
free-living in the environment and parasitic according to the
surrounding conditions. e.g. Strongyloides stercoralis and
Naegleria fowleri.
4. An accidental parasite:- that affects an unusual host e.g.
2-Types of according to the nature of
living

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3-Types of parasites according to
their duration with their hosts
1. A temporary parasite:- the parasite that visits the host
only for feeding and then leaves it. e.g. Bed bug visiting man
for a blood meal
2.A permanent parasite:- the parasite that lives in or on its
host without leaving it e.g. Lice.
3.An opportunistic parasite:- the parasite that is capable of
producing disease in an immunodeficient host (like AIDS and
cancer patients). In the immunocompetent host, it is either
found in a latent form or causes a self limiting disease e.g.
Toxoplasma gondii.

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1.Intraspecific parasites :both the parasites and the hosts
belong to the same species such as in human fetus
2. Interspecific parasites: parasite belongs to a species
and its host belongs to another species such as in the
majority of parasites
3. A zoonotic parasite:- that primarily infects animals and
is transmittable to human. e.g. Fasciola species
4-Types of parasites according to
their affinity with their hosts

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*What is a host
*Host :-
*Is defined as an organism, which
harbors the parasite and provides
nourishment and shelter to latter
and is relatively larger than the
parasite.

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The host may be of the following types: -
1.Definitivehost:Thehost,inwhichtheadultparasite
livesandundergoessexualreproductioniscalledthe
definitivehost,e.g.mosquitoactsasdefinitivehostin
malaria.Thedefinitivehostmaybeahumanorany
other living being.
2.Intermediatehost:Thehost,inwhichthelarval
stageoftheparasitelivesorasexualmultiplication
takesplaceiscalledtheintermediatehost.Insome
parasites,twodifferentintermediatehostsmaybe
requiredtocompletedifferentlarvalstages.These
k fi d di dih
Types of Hosts

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Types of
Hosts3-Paratenic host : A host, in which larval stage of the
parasiteremainsviablewithoutfurtherdevelopmentisreferredasa
paratenichost.Suchhosttransmitstheinfectiontoanotherhost,e.g.fish
for plerocercoid larva of Diphyllobothrium latum .
4-Reservoirhost:Inanendemicarea,aparasiticinfectionis
continuouslykeptupbythepresenceofahost,whichharborsthe
parasiteandactsasanimportantsourceofinfectiontoothersusceptible
hosts, e.g. dog is the reservoir host of hydatid disease.
5-Accidentalhost:Thehost,inwhichtheparasiteisnotusuallyfound,e.
g. man is an accidental host for cystic echinococcosis.

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Host-parasite relationships host-
parasite relationships

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A Busy Course!
What are the differences between parasite and host?
Discuss that in small groups of 3-4 student
Be prepared to share three reasons with the large group.
(5 minutes brainstorming , 5 minutes share-out )

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LIFE CYCLE OF PARASITES
1.Directlifecycle:whenaparasiterequiresonlysinglehostto
completeitsdevelopment,itiscalledasdirectlifecycle,e.g.
Entamoebahistolyticarequiresonlyahumanhosttocomplete
its life cycle.
2.Indirectlifecycle:whenaparasiterequirestwoormore
speciesofhosttocompleteitsdevelopment,thelifecycleis
calledasindirectlifecycle,e.g.malarialparasiterequiresboth
human host and mosquito to complete its life cycle.

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* Life Cycle of Human Parasites
*The key to understanding the transmission of a
parasite species and parasitic disease is its life-
cycle
*Generalized stages of a parasite’s life cycle
*Stage in human host (linking to pathogenesis)
*Stage to discharge (diagnostic stage)
*Stage developing outside human host(in external
environment, intermediate host or insect host)---
(linking to transmission)
*Stage infecting men (infective stage)

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SOURCES OF INFECTION
1-Contaminated soil and water:
2-Food:
3-Vectors:Avectorisanagent,usuallyanarthropodthattransmitsan
infectionfrommantomanorfromotheranimalstoman,e.g.female
Anopheles is the vector of malarial parasite.
4-Carrier:Apersonwhoisinfectedwithparasitewithoutanyclinicalor
subclinicaldiseaseisknownascarrier.Hecantransmitparasiteto
others. For example, all vertical transmission of congenital infections.
5-Self(autoinfection:-Finger-to-mouthtransmission,e.g.pinworm ,
Internal reinfection, e.g. Strongyloides.

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►Parasitic infections may remain inapparcnt or
give rise to clinical disease. A few organisms,
such as E. histolytica may live as surface
commensals, without invading the tissue.
► Clinical infection produced by parasite may
take many
forms: acute, subacute, chronic, latent, or
recurrent.
PATHOGENESIS

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Pathogenic mechanisms of parasite
►Pathogenic mechanisms, which can occur in parasitic
infections are:
qTissue Damage
qThree major types of histopathological cell damage occur in parasite-injured tissues:
q1. Parenchymatous or Albuminous Degeneration
qThistypeofdamageischaracterizedbyswollencellspackedwithalbuminousorfattygranules,
indistinctnuclei,andpalecytoplasm.Itisoftenseenintheinfectedliver,cardiacmuscleand
kidney cells.
q2. Fatty Degeneration
qThistypeofdegenerationresultsinthedepositionofabnormalamountsoffatincells.Thistypeof
degeneration imparts a yellowish color to the cells and is common among parasite-laden liver cells.
q3. Necrosis
qPersistentcelldegenerationofanytypecausesdeathofcellsortissues.Thedeadcellsgivetissues
anopaqueappearance.Forexample,encystmentandcalcificationofTrichinellaspiralislarvae

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B- Tissue Changes
Cellandtissueparasitessometimesevokechangesinthegrowthpatternofthe
affectedtissue.Someofthesechangesareveryharmful;othersaremerely
structuralwithnoserioussystemicconsequencestothehostorganism.These
tissue changes of parasitic origin are of four major types:
1. Hyperplasia
2. Hypertrophy
3. Metaplasia
4. Neoplasia

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*Epidemiology
Epidemiology:
Itisthescienceconcernedwiththefactorsthatdeterminetheprevalence
ofinfectionandtheincidenceofadisease.Itisthehistoryofthedisease,
includinginfectioninmanandanimalsandagentsthatserveasreservoirs
and vectors.
*Infectionsmaintainedatamoreorlessstablerateofprevalencewithin
the human population of an area are said to be endemic.
*If there is a high prevalence, it is hyperendemic.
Prevalence:
Representingthenumberofinfectedindividualsatagiventimeina
designated area.
Incidence:
Is the rate or frequency of disease (or new infection) occurring.
*Iftheinfectionappearsirregularlyinscatteredindividuals,itiscalled
sporadic;andifitdevelopsahighprevalencethroughunusuallyrapid
transmission, it is called epidemic.

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*Treatment of Parasitic
Infection:
The successful treatment includes
Medical and Surgical measures.
* Adequate nutrition to build up general resistance.
* Specific chemotherapy, the successful chemotherapy
depends upon the use of a drug that has a minimal
toxic effect on the tissues of the host and lethal action
on the parasite.
* New chemotherapeutic agents are being constantly
developed, and therapeutic methods are continually
undergoing revision.

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