1.INTRODUCTION TO MEDICAL PARASITOLOGY.ppt

Medical parasitology introduction is one of the course unit under microbiology which is taught at medical institution to boost their understanding about parasitic infections

1. INTRODUCTION TO MEDICAL
PARASITOLOGY
Abura Geoffrey
Kampala International University-
Western Campus

2. Father of parasitology
Karl Rudolphi (1771–1832)

3. Branchesofmedicalparasitology
1-MedicalHelminthology:Dealswiththestudyof
helminthes(worms)thataffectman.
2-MedicalProtozoology:Dealswiththestudyof
medicallyimportantprotozoa.
3-MedicalEntomology:Dealswiththestudyof
arthropodswhichcauseortransmitdiseasetoman.

4. NAMING OF PARASITES
•Allanimalsandplantsmusthavenamesbywhichthey
canbedistinguished.
•Thefirstnameinthebinomialisthatofthegenusto
whichtheorganismbelongs,andthesecondisthatof
thespecies.
•Thiscombinationofindesignatingananimalorplant
speciesistermedbinomialnomenclature.

5. Classification of parasites
Parasitesare classifiedinto:-
1.Protozoa
2.Helminthes

6. PROTOZOA
•Theseareunicellularorganismswhichmultiply
bybinaryfission.
•Asinglecellperformsallfunctionsofthe
organism.
•Protozoaaresinglecelledanimals,occurring
asfreelivingorganismsandasparasites.
.

7. Characteristics
Theycannotbeseenwithanakedeye,butwithuseofamicroscope.
Theyaremuchlargerthanmostbacteria.
TheypossessanucleuswithDNAorRNAsurroundedbyalimitingmembrane
withcytoplasmandarethereforereferredtoaseukaryotic.
Theyrangefrom5–50micrometer
Theymovefreelywithaidofpseudopodiatoallowmovement.Othersuse
flagellaorciliaformovement.
Protozoahavetruenutritioni.e.theyingest,digest,assimilateandexcrete.
Theyphagocyticmechanismi.e.theyengulffoodsubstrate.
Theyreproduce/replicateasexuallybybinaryfission,andsexuallywithgamete
formation.
Theyformcystswhichenablethemtosurviveinharshconditionsoutsidethe
host.

8. HELMINTHIASIS (WORM INFESTTATIONS)
Helminthiasisisadisease/conditionresultingfrom
aninfestationwithparasiticworms.
Helminthesareeukaryoticparasiticwormsthatlive
mainlyinthehumanGIT.Manistheonlyreservoir.
Unlikebacteria,protozoaandviruses,helminthes
areoftenlargeorganisms.
Worminfestationsarecommonindeveloping
countriesandaffectchildrenmorethanadults.

9. Con’t
Thecommonhelminthesfoundinadultorsexual
forminthehumanbodyare:
Roundworms(ascarislumbricoides)
Pinworms/threadworms(enterobiusvermicularis)
Hookworms(ancylostomaduodenaleand
necatoramericanus)
Tapeworms(taeniasaginata,taeniasolium)

10. Transmission of worms occurs through
Faecal-oralroutei.eingestionof
infectivelarvafromanotherinfected
hostegeatingundercookedinfected
pork
Penetrationoftheskinespeciallyin
peoplewhowalkbarefooted

11. Classification

12. GROUP GENUS/ SPECIES MODE OF LOCOMOTION
Amoeba Entamoeba histolytic a Pseudopodia
Flagellates Leishmaniadonovani
Giardia lamblia
Trichomonas
vaginalis

Flagella
Sporozoa Plasmodium species
Plasmodium vivax
Plasmodium
falciparum
Plasmodium ovale
Plasmodium
malariae
Toxoplasma species



Nil

Cilliates Balantidium c oli Cilia
Protozoaaresubclassifiedbasingontheirorganof
locomotion

13. Protozoa Disease c aused
Entamoeba histolytic a Amoebic dysentery
Plasmodium species
 Plasmodium vivax
 Plasmodium ovale
 Plasmodium malariae
 Plasmodium falciparum
Malaria
Giardia lamblia Diarrheal diseases
Trichomonas vaginalis Vaginitis (trichomoniasis)
Trichomonas hominis Diarrhea
Tripanosomabrucei
Tripanosomagambiense
Tripanosomarhodesiense
Tripanosomiasis
Balantidiun c oli Balantidiasis
Toxoplasmgondii Toxoplasmosis
Leishmaniadonovani Kala azar, the black sickness
Cryptosporidium Cryptosporidiosis
Microsporidia Microsporidiosis

14. DefinitionofTerms Used in
Parasitology
•Parasitology:-isasciencethatdealswithparasites.
•MedicalParasitology:-Thesciencethatdealswithparasites
thatliveinoronotherorganismscalledtheirhostsandcausing
injurytothem.
•Parasite:-isanorganismlivingtemporarilyorpermanentlyin
oronanotherorganism(host)fromwhichisphysicallyor
physiologicallydependentuponother.

15. Nature of Parasites-
•Aparasitecanbeunicellular,wormoranarthropod.
FeaturesofParasites
•Smallerthantheirhost,
•Outnumberthehost,
•Shortlifespanthantheirhost
•Havegreaterreproductivepotentialthantheirhost.

16. Parasites can be Classified:-
•Accordingtotheirhabitat:
1.Ectoparasites:parasiteslivingonoraffectingtheskin
surfaceofthehost.E.g.lice,tick,etc.
2.Endoparasites:Parasiteslivingwithinthebodyofthe
host.E.g.Leishmaniaspecies,Ascarislumbricoides,etc.

17. According to their dependence on
the host:
1.Permanent(obligate)parasites:Theparasitedepends
completelyuponitshostformetabolites,shelter,and
transportation.Thisparasitecannotliveoutsideitshost.E.g.
Plasmodiumspecies,Trichmonasvaginalis,etc.
2.Temporary(facultative)parasite:Theparasiteiscapableof
independentexistenceinadditiontoparasiticlife.E.g.
Strongyloidsstercolaris,Naegleriafowleri,etc.

18. According to their Pathogenicity:
1.Pathogenicparasites:-Itcausesdiseaseinthehost.E.g.,E.
histolytica
2.Non-Pathogenic(commensal)parasite:-Theparasitederivesfood
andprotectionfromthehostwithoutcausingharmtothehost.E.g.
Entamoebacoli
3.Opportunisticparasites:-Parasiteswhichcausemilddiseasein
immunologicallyhealthyindividuals,buttheycauseseveredisease
inimmuno-deficienthosts.E.g.Pneumocystiscarnii,Toxoplasma
gondii,Isosporabelli

19. Host
•Hostsareorganismwhichharborstheparasite.

20. Types of Hosts:-
1.Definitivehost:-
Dependingontheparasiticspecies,itiseitherahost
whichharborstheadultstageofaparasiteormost
highlydevelopedformoftheparasiteoccurs;or
sexuallymaturestagesofaparasiteandfertilization
takesplaceinit,e.g.,manisthedefinitivehostof
Taeniasaginata.

21. Con’t
2.Intermediatehost:-Isahostharboringsexuallyimmatureorlarvalstage
ofaparasiteandinwhichnofertilizationtakesplaceinit.E.g.Cowisthe
intermediatehostforTaeniasaginata.

22. Con’t
3.Reservoirhost:-Awildordomesticanimalwhich
harborsaparasiteandactsassourcesofinfectionto
humans.
4.Carrierhost:-Ahostharboringanddisseminatinga
parasitebutexhibitingnoclinicalsign.
5.Accidental(Incidental)host:-Infectionofahostother
thanthenormalhostspecies.Aparasitemayormaynot
continuefulldevelopmentinthishost.

23. Vector:-
•Anyarthropodorotherlivingcarrierwhichtransportsa
pathogenicmicroorganismsfromaninfectedtonon-
infectedhost.
•A.Biologicalvectors:-
•ThosevectorsthatcompletethelifecycleaparasiteE.g.
Anopheles(VectorofPlasmodium),Phlebotomus(Vectorof
Leishmania),Glossina(vectorofTrypanosoma),Simulium(Vector
ofOnchocerca),etc.

24. Con’t
•B.Mechanical(Parathenicortransport)Vectors:
•Theyarepassivecarriersofparasites,notessentialinthelifecycle.E.g.
HouseflyandChockroachasamechanicalvectorforAmoebae,Giardia,
etc.

25. Disease terminologies
•DiagnosticStage:-Adevelopmentalstageofapathogenic
organismthatcanbedetectedinstool,blood,urine,sputum,CSF
orotherhumanbodysecretions.
•InfectiveStage:-Thestageofparasiteatwhichitiscapableof
enteringthehostandcontinuedevelopmentwithinthehost.
•Infection:-Invasionofthebodybyanypathogenicorganismand
thereactionofthehoststissuetothepresenceoftheparasiteor
relatedtoxins.

26. Con’t
•Infestation:-Theestablishmentofarthropodsuponorwithina
host.
•Zoonosis:-Diseasesofanimals.Todaythistermisappliedforthose
diseasesthataretransmittabletoman.
•BiologicalIncubation(Prepatent)Period:-Itistimeelapsing
betweeninitialinfectionwiththeparasiteanddemonstrationof
theparasitesortheirstagesinexcreta,blood,aspirateandother
diagnosticmaterial.

27. Con’t
•ClinicalIncubationPeriod:-Itistheintervalbetweenexposure
andtheearliestmanifestationorinfestation.
•Autoinfection:-Aninfectedindividualactsasasourceforhyper-
infectiontohimself.
•Superinfection(Hyper-infection):-Whenanindividualharboring
theparasiteisreinfectedbythesameparasite.
•Retroinfection:-Aretrogradeinfectioncausedbythenewly
hatchedlarvaofE.vermicularisfromtheperianalregiontoreach
thecolon,wheretheadolescentformoftheparasitedevelop.

28. Modeofparasiticinfections:
•Directcontactthroughtheskinorsexually.
•Ingestionofcontaminatedfoodandwaterorundercooked
meatinwhichtheinfectivestagehasdeveloped.
•Penetrationoftheskinduetocontactwithinfectedsoilor
waterstream.
•Inhalationofdustcarryingtheinfectivestageofparasite.
•Vectors:throughthebiteorfaecesofinfectedvectororby
swallowingthevector.
•Autoinfection:occurswheninfectivestagesarecarriedfrom
faecestomouthofpatient.

29. Major Routes of Transmission of
parasitic infection
1-Mouth:mostcommon:Ingestionofinfectivestage,e.g.
protozoancysts&embryonatednematodeeggs.Intimate
oralkissing,e.g.Entamoebagingivalis.
2-Skinpenetrationofinfectivelarvalstagetoskin:Directly:
e.g.CercariaofSchistosoma&filariformlarvaofhookworm.
Indirectly(throughinsectvectors),e.g.infectivestageof
trypanosome
3-Airborne:Parasiteinhalednosenasopharynx
intestine,e.g.E.vermicularis.Parasiteinhalednose
bloodorlymphaticspecifictissues,e.g.T.Gondii&free
livingamoeba.
4-Transplacental:Parasitefrommothertofoetus

30. Host –Parasite Relationship
1.Commensalism:2animalsofdifferentspecieslivetogether
withoutmetabolicallydependentontheother,althoughone
organismmayreceivesomebenefitbutdoesnotharmthe
other.
2.Mutualism:Wheresharedbenefitsarepresent;onecannot
surviveintheabsenceoftheother
3.Parasitism:whereanorganismlivinginoronanotherliving
organism,causingsomedegreeofdamagetoitshost

31. Diagnosis
Clinical Diagnosis
Clinical Picture –Symptoms -Signs
Laboratory Diagnosis
-Direct Methods: Demonstration of the diagnostic parasitic stage, in urine
or stool or blood or sputum, under microscopy
-Indirect Methods:
*Detection of Antibodies (Abs) by serological tests [IHAT-IFAT-ELISA]
*Detection of Antigens (Ags)
Imaging Methods
X-Ray –Ultrasonography–Ct Scan -MRI

32. EFFECT OF PARASITES ON THE HOST
•(a)Directeffectsoftheparasiteonthehost
•Mechanicalinjury-maybeinflictedbyaparasitebymeansof
pressureasitgrowslarger,e.g.Hydatidcystcausesblockageof
ductssuchasbloodvessels
•Harmfuleffectoftoxicsubstances-inPlasmodiumfalciparum
productionoftoxicsubstancesmaycauserigorsandother
symptoms.
•Deprivationofnutrients,fluidsandmetabolites-parasitemay
producediseaseby
•competingwiththehostfornutrients.

33. (b) Indirect effects of the parasite on the host:
•Immunologicalreaction:Tissuedamagemaybecausedby
immunological
•responseofthehost,e.g.nephriticsyndromefollowing
Plasmodiuminfections.
•Excessiveproliferationofcertaintissuesduetoinvasionbysome
parasitescan
•Alsocausetissuedamageinman,e.g.fibrosisofliverafter
depositionoftheovaofSchistosoma.

34. Host Susceptibility Factors
•Notallparasiticinfectioncausesdiseaseofclinicalsignificance.
•Bothhostandparasiticfactorsareinvolved.

35. Host Factors
1.Geneticconstitution
2.Age
3.Sex
4.Levelofimmunity:naturalandacquiredimmunity.
5.Nutrition(malnutritionorundernutrition)
6.Intensityandfrequencyofinfections
7.Presenceofco-existingdiseaseorconditionswhichreduces
immuneresponse.e.g.Pregnancy,HIV
8.Lifestyleandoccupation

36. Parasite factors
Strainoftheparasiteandadaptationtohumanhost
Parasiteload(numberofparasite)
Site(s)occupiedinthebody
Metabolicprocessoftheparasite,particularlythe
natureofanywasteproductsortoxinsproducedbythe
parasiteduringitsgrowthandreproduction.

37. Escape mechanism of parasite from
the immune system
Parasitescanevadethehostimmuneresponsesbyvariety
mechanisms:
1.SiteIntracellularparasitesasT.cruzi,Leishmaniaandthe
intracellularstageofPlasmodiaaretosomeextentprotected
fromtheactionofantibodiesasarethoseformingcystsasT.
gondiiandlarvaofT.solium,EchinococcusandTrichinella
spiralis.ParasitelivinginmacrophagesasToxoplasma,T.cruzi
andLeishmaniaareabletoavoidorinactivatethelysosomal
enzymes,whicharethecellsweaponsofoffencesagainst
microbialorganisms.

38. Con’t
1.Avoidanceofrecognition:Thiscanbeaccomplishedby:
a.Productionofsuccessivewavesofprogenywithdifferent
surfaceantigens(i.e.,variationofantigens)asinAfrican
trypanosomes.
b.Molecularmimicry:Certainparasitesarerecognizedasselfand
consequentlydonotstimulateimmunologicreactionsintheir
host.ThusSchistosomewormsarecapableofmaskingtheir
foreignersbyacquiringasurfacelayerofhostantigenswhich
possiblyprotectthemfromantibodydamage.Thesearecalled
“eclipsed”antigens,sincetheseantigensbyresemblingthoseof
thehostarenotrecognizedasforeignandthereforearehidden

39. Con’t
•fromtheimmunerecognition.Thisphenomenonofantigen
sharingbetweenaparasiteandahostiscalledMolecular
mimicry.
3.Suppressionofimmuneresponse:Severalparasiticspeciese.g,
Plasmodium,Toxoplasm,TrypanosomaandTrichinellaareableto
suppresstheabilityofthehosttorespondimmunologically.This
sometimes,resultsinanincreaseintheseverityofanyviralor
bacterialinfectionalsopresent.Immuno-supressionisdueto
productionbytheparasiteoflargequantitiesofsolubleantigens
which:3.1.Combinewiththeantibodyandpreventingitfrom
attachingtotheparasite3.2.InduceBorT-celltoleranceeitherby
blockingantibodyformingcellsorbydepletingthestockofmature
antigen-specificlymphocites(clonalexhaustion).3.3.Activating
specificsuppressorcells(T-cellsormacrophages).

40. General Life Cycles of Parasites
•Directlifecycle:Aparasitethatcancompleteitslife
cycleinasinglehost.
•E.g.,S.stercoralis,Hookworms,G.lamblia,E,.
histolytica,etc.
•Indirectlifecycle:Whenaparasiterequiresan
intermediatehostorvectortocompleteits
development.
•E.g.,Plasmodiumspecies,Leishmaniaspecies,Taenia
species.etc.

41. Types of specimen used for
parasitological examination
•Stool:-.e.g.,intestinalnematodes,cestodes,trematodesand
protozoa.
•Blood:-e.g.,Haemoparasites
•Urine:-e.g.,S.hematobium,T.vaginalis,
•Sputum:-e.g.,P.westermani.
•Skin:-e.g.,L.aethopica,O.volvulus,D.medinensisandE.
vermiculari
•Cerebro-Spinalfluid:-e.g.,TrypanosomarhodisenseandNaegleria
fowleri.

42. Con’t
•Bonemarrow:-e.g.,L.donovaniandT.gondiiLymphgland
aspirates:-e.gTrypanosomarhodisense,L..donovaniandT.gondii
•Liveraspirate:e.g.,E.histolytica,L..donovaniandT.gondii
•Spleenaspirate:-e.gL..donovaniandT.gondii
•Musclebiopsy:-e.g.,T.spiralis
•Rectalscraping:-e.g.,SchistosomaspeciesDuodenalaspirate:-
e.g.,G.lamblia,F.hepaticaandS.stercoralis
•Bronchialbiopsy:-e.g.,P.carnii
•Perianalswab:-e.g.,E.vermicularis

43. Review Questions
1.Whatisthedifferencebetween?
a.Commensalismandparasitism
b.Obligateandtemporaryparasite
c.Definitiveandintermediatehost
d.Biologicalvectorandmechanicalvector
2.Listthesourcesofexposuretoparasite.
3.Mentionpossibleparasitesthatarefoundinthefollowingspecimens
a.Stoolb.Bloodc.Urined.Sputume.CSF
4.Identifythepossiblesourcesofspecimenforthefollowingparasites
a.Schistosomamansoni
b.E.vermicularis
c.Trypanosomespecies
d.Filariaworms
e.Giardialamblia
5.Parasitesthathaveindirectlifecyclearemoredifficulttocontrol.Why?