Introduction to Medical Parasitology Victoria Basa-Dalay, MD, MSc July 1, 2010
Introduction to Medical Parasitology
Victoria Basa-Dalay, MD, MScJuly 1, 2010
Differentiate the three symbiotic relationships in Microbial World
Define: Parasitology, Parasite, Host and other commonly used terms in Parasitology
Discuss the taxonomic classification of parasites with examples
Given the life cycle of a parasite:identify its important componentsGive its simple preventive and control measures
LEAD Rules of the Session
Listen to learn and learn to listen
Expect the unexpected
Active participation is encouraged
Discuss and Share your thoughts
An association between two different species of organismsPrimarily aim for obtaining food from one or both member of the relationshipCommonly known as “Living together”Has no overtones of benefit or harmIncludes a wide diversity of associations
Symbiosis
BASIC TERMINOLOGY & PRINCIPLES
Symbiotic Relationships
ParasitismUnilateral benefit
MutualismReciprocal benefit
CommensalismShelter and food
Symbiosis
Degree of
harmto
host
closeness of association
Benefit of the species
Self-Assessment: Comment on this table
Type of SymbioticRelationship
Organism Host
Mutualism + (Benefited) - (Not Harmed)
Commensalism
- (Not Harmed)
+( Benefited)
Parasitism ++ (Benefited)
- ( Not Harmed)
Parasitology
“The science that deals with specialized group of animals which are physiologically dependent on other organisms for their survival”. Neva & Brown, 1994
Medical Parasitology:
“The science that deals with parasites (organisms) that take up their abodes, temporarily or permanently, on or within its hosts (other living organisms) for the purpose of procuring food and protection, resulting in a relationship that can harm or lead to disease development in host ”.
Definition
ParasiteOrganisms ranging from microscopic to macroscopicExhibit great diversity in morphology and physiologyAnimals depending on bigger organisms for food and shelterHas intimate almost always obligatory relationship with the hostAlways harmed the host
Ascaris lumbricoidesCompetes for available nutrients since it absorbs sugars, proteins and fats from the foodObstructs the gut by bolus of wormsDamages vital organs during erratic migration
SURVIVAL FACTORS OF PARASITES
Parasites have successfully adapted to (all?) environmental “niches” in hosts
Parasites best adapted are least pathogenic
Typically with long-term/chronic/”intimate” parasite-host relationships
Types of Parasites to REMEMBER
Endo- vs Ecto-parasites
Obligate vs Facultative Parasites
Permanent vs Transient/ Temporary Parasites
Erratic vs Spurious Parasites
Zoonotic Parasites / Accidental Parasites
CONDITIONS NECESSARY FOR SUCCESSFUL ENDEMIC PARASITISM
Reservoir of infection – source of infection
Means of transmission from infected to susceptible, “new” hosts
Ability to invade and successfully reside in “new” hosts
Ability to reproduce
Definition
HostThe bigger organism in which the parasite livesProvides the nourishment and protection /shelter needed by the parasitesMay transfer or harbor the organism temporarily or permanentlyProvide appropriate environment for growth and reproductionMaybe harmed, killed , not affected or they may even benefit in association with other organism
Types of Host
Definitive HostHarbors the sexual or the mature stage of the parasitesite where the sexual reproduction occurs, if present.
Eg. Man - AscarisDog - DypilidiumMosquitoes - Plasmodium
Host’s Body:Man, Pig
External Environment
DEFINITIVE HOST:
Man or Pig
Types of Host
Intermediate HostHarbors the asexual or the immature/ larval forms of the parasiteSite where the asexual reproduction occurs
Eg. Snails - Echinostoma Pig - Trichinella and Taenia Man - Plasmodium Crustaceans – Paragonimus
In HumansIn Snails or
Crustaceans
Types of Host
VectorAn invertebrate animal which transmits a parasitic organism from one host to another
Types of VectorsMechanical VectorBiological Vector
Humans Mosquito
2 weeks
Infectious for
other people
Types of Host
VectorMechanical VectorAn invertebrate animal which merely transfer parasitic organism from one host to another by their appendages
Eg. flies, cockroaches
Biological VectorAn invertebrate animal which harbor the parasitic organism internally with further development
Eg. mosquitoes, bugs
In Mosquito
Life cycles of Human ParasitesDirect Life cycleNo intermediate host is needed/required in transmitting the parasite from one host to anotherA. Parasite may be
immediately infective upon leaving the host
B. Parasite may still need an external environment
(soil) to develop into an infective stage
A. Trichomonas
B. Trichiuris
In the Body of Host
External Environment
Host 1 Host 2
Life cycles of Human ParasitesIndirect Life cycle
At least one (1) intermediate host is needed or a vector is required in transmitting the parasite from one host to another
Eg. Fasciolopsis Plasmodium
In the Body of Host
In the Snail andWater Plants
Habitat:
Small Intestine
Diagnostic Stage:
Egg in Feces
Infective Stage:
Embryonated Egg
Portal of Exit:Anus
Portal of Entry:
Mouth
Mode of Transmission: Ingestion of the infective stage
Path of Migration:
Blood
Lungs
IntestineExternal Environment : Soil (10 - 14 days)
Components of the Life Cycle
GENERALIZED PROTOZOAN LIFE CYCLE
Trophozoite
Cyst
GENERALIZED PROTOZOAN LIFE CYCLE
Trophozoite
Trophozoite
GENERALIZED SPOROZOAN LIFE CYCLE
Trophozoite Sporozoite
Schizont
Gametocyte Gametes Oocyst
Ookinete
Life Cycle of Ascaris lumbricoides
Habitat:
Small Intestine
Early diagnosis
Cooking food properly
Proper excreta disposal
Prophylactic Treatment of Cases
Mode of Transmission: Ingestion
Early Treatment of Cases
Avoid use of night soil
Proper excreta disposal
Early Treatment of Cases
Taxonomic Groupings of Parasites
Unicellular, eukaryotic parasites- Protozoan
Phylum SarcomastigophoraPhylum ApicomplexaPhylum MicrosporaPhylum Ciliophora
Multicellular parasites - MetazoanHelminths
Phylum AschelminthesPhylum Platyhelminthes
ArthropodsPhylum Arthropoda
Common terms used in Protozoans
Trophozite: the active,feeding and growing stage in most protozoans; the mature form
Cyst: the sac-like stage in protozoans, usually the infective stage
Oocyst: A thick-walled structure in which sporozoan zygotes develop and that serves to transfer them to new hosts like in mosquitoes.
Types of Parasites
According to Taxonomic Group
Protozoans
FlagellatesSubphylum Sarcodina
•Move by pseudopodiaEg. Entamoeba NaegleriaAcanthamoeba
Subphylum Mastigophora
•Move by flagella
Eg. Giardia, Trypanosoma, Leishmania, Trichomonas
Reproduce Asexually by Binary fission
Amoeba
Entamoeba histolytica
Disease: Amoebic dysentery/ colitisMode of Transmission: ingestion of cysts from contaminated food or waterInfective Stage: cysts Diagnostic Stages: cysts and trophozoitesHabitat: colonFx: anchovy sauce; flask-shaped ulcerDx: FecalysisTx: Metronidazole
Subphylum Sarcodina
Naegleria fowleriDisease: Acute Amoebic Meningo-encephalitis in Normal HostsMode of Transmission: Penetration of the nasal mucosa to the brainInfective Stage: trophozoite Diagnostic Stages: trophozoitesHabitat: brain Fx: Clinical presentations like fatal meningitis ( rapid onset)Dx: Trophozoites in CSF/ Brain tissueTx: Amphotericin B
Subphylum Sarcodina
Types of Parasites
According to Taxonomic GroupProtozoans
FlagellatesSubphylum Mastigophora
•Move by flagella
Eg. Giardia, Trypanosoma, Leishmania, TrichomonasReproduce Asexually by Binary
fission
Giardia lamblia
Disease: GiardiasisMode of Transmission: ingestion of cysts from contaminated water and foodInfective Stage: cysts Diagnostic Stages: cysts and trophozoitesHabitat: small intestineFx: steatorheic stool; dysenteryDx: Fecalysis and EnterotestTx: Metronidazole
Subphylum Mastigophora
Trypanosoma cruziDisease: Chaga;s Disease; AmericanTrypanosomiasisMode of Transmission: bites of reduviid bug (Triatoma,)
Infective Stage: metacyclic trypomastigoteDiagnostic Stages: epimastigoteHabitat: skin, mucous membrane; bloodFx: chagoma,Romana sign; megacolon; cardiomyopathy ( most serious Cx)Dx: Blood smear; body fluidsTx: benznidazole or nifurtimox
Subphylum Mastigophora
Trypanosoma brucei
Disease: African Trypanosomiasis, Sleeping SicknessMode of Transmission: bites of infected tsetse fly( Glossina) Infective Stage: metacyclic trypomastigoteDiagnostic Stages: epimastigoteHabitat: body fluids; bloodFx: somnolence; siezure; comaDx: Blood smear; body fluids NNN mediaTx:Pentamidine isethionate
and Sudamin
Subphylum Mastigophora
Trichomonas vaginalis
Disease: TrichomoniasisMode of Transmission: direct sexual contactInfective Stage: trophozoiteDiagnostic Stages: trophoziteHabitat: vagina and prostateFx: vaginal prostatic discharge discharge and itchinessDx: Wet smear of vaginal dischargeTx: Metronidazole
Subphylum Mastigophora
Types of Parasites
According to Taxonomic Group
ProtozoansPhylum Apicomplexa
No locomotory organ
Have a complex life cycleEg. Plasmodium, Isospora, Toxoplasma. Cryptosporidium
Phylum MicrosporaNo locomotory organ
Intracellular ParasiteEg. Microsporidia
With alternating sexual and asexual reproduction
Sporozoa
Plasmodium spp. Disease: Malaria; Blackwater FeverMode of Transmission: bites of infected female anopheline mosquitoInfective Stage: sporozoitesDiagnostic Stages: blood stagesHabitat: bloodFx: tertian and quartan periodicityDx: Blood smearTx: Chloroquine; quinine;
quinghaosu
Phylum Apicomplexa
Cryptosporidium spp. Disease: Malabsorption syndrome; CrypstosporidiosisMode of Transmission: drinking or contact with contaminated waterInfective Stage and Diagnostic Stages: small, sporulated oocyst with 4 sporozoitesHabitat: Small intestineFx: cachexia and severe diarrheaDx: Fecalysis
Tx: Nitazoxanide; fluid and electrolyte replacement
Phylum Apicomplexa
Types of Parasites
According to Taxonomic Group
ProtozoansPhylum Ciliophora
Move by beating of many cilia
Mostly include variety of free-living and symbiotic species
Eg. Balantidium coli
Reproduce asexually by Binary Fission
Ciliates
Balantidium coliDisease: BalantidiasisMode of Transmission: drinking or contact with contaminated waterInfective Stage and Diagnostic Stages: cysts and trophozitesHabitat: Large IntestineFx: diarrhea among slaughter house workersDx: FecalysisTx: Tetracycline*, with Metronidazole*
Phylum Ciliophora
Types of Parasites
According to Taxonomic Group
HelminthsPhylum: Aschelminthes Elongated, cylindrical worms
Unsegmented
Sexes are separate
Reproduction by:
Oviparous Eg. Ascaris, Enterobius
Viviparous Eg. Trichinella, Filarial Worms
Parthenogenetic Eg. Strongyloides
Infection by:
Ingestion of Eggs Eg. Ascaris, Trichuris
Skin Penetration of larvae Eg. Hookworm
Vector-borne Eg. Filarial Worms
Ingestion of of encysted larvae Eg. Trichinella
Class: Nematoda
Intestinal and tissue inhabiting species
HELMINTH/WORM TERMINOLOGY Adults: sexually reproductive stage in
the life cycle stage
Larvae: developmental or asexually reproductive stage in the life cycle
Eggs: spherical/ oval stage that protects the zygote &/or embryo in the life cycle
Cysts: usually an encapsulated larval stage found in tissues of an intermediate host
HELMINTH/WORM TERMINOLOGY
Monoecious/hermaphroditic: both sexes in one body
Dioecious: with sexes separate; males & females
Parthenogenesis: ability to produce offspring without fertilization of eggs
Worm-terms, continued
Oviparous: production of eggs, discharged from uterus of female
Ovoviviparous: production of eggs which hatch prior to discharge from uterus of female
Viviparous: production of embryos/L1 larvae, no rigid encapsulation of embryo
Nematodes of Medical Importance
Habitat Genera
Gastrointestinal tractSmall Intestine
Large Intestine
Ascaris,Ancylostoma Necator,Trichinella,CapillariaTrichiuris, Enterobius
Skin/ Tissue nematodes
Onchocerca, Loa, Gnathostoma, Trichinella
Blood and Lymphatic Nematode
Wuchereria, Brugia
CNS Nematode Angiostrongylus
Hookworm. Disease: Ancylostomiasis, NecatoriasisMode of Transmission: Skin penetrationof filariform larvaeInfective Stage: Filariform LarvaeDiagnostic Stages: OvaHabitat: Small IntestineFx: Ground itch; Iron deficiency anemiaDx: Fecalysis
Tx: Mebendazole
Class: Nematoda
GENERALIZED NEMATODE LIFE CYCLE
AdultsEggs Embryos
L1
L2 larva
L3 larva
L4 larva
L5 juvenile
Filarial Worm Life Cycle
DH (Man) Vector(Mosquitoes)
Adults microfilariae L1 L2 larva L4 larva L3 larva
L5 larva
Wuchereria bancrofti
Disease: Lymphatic filariasisMode of Transmission: bites of infected mosquitoesInfective Stage: Third stage larvae (L3)Diagnostic Stage: Microfilariae (L1)Habitat: Lymphatic system; skin and glandsFx: elephantiasisDx: Blood smear
Tx: Mebendazole
Comparison of Nematode Eggs
Types of Parasites
According to Taxonomic Group
Helminths Phylum: Platyhelminthes Flattened, leaf-shaped
or cylindrical worms ( Schistosoma)
Unsegmented
Hermaphroditic
Reproduction by:
Oviparous Eg. Schistosoma
Infection by:
Ingestion of metacercariae Eg. Fasciola, Echinostoma, Paragonimus, Clonorchis
Skin Penetration of cercariae Eg. Schistosoma
Class: Trematoda
Trematodes/FlukesGeneralized Fluke Life Cycle
Adults in Man (DH)Egg Miracidium (embryo) First IH
(Snail)
Sporocyst &/or Redia larva
Cercaria
Second IH ( vegetations, crabs, fish, snail)
Metacercaria
Typical Trematode Life Cycle
1st IH
2nd IH
Flatworm helminths, continued
Schistosomes/Bloodflukes Generalized schistosomal life cycle
Man (DH) Male & Female Adults
Egg Miracidium embryo Snail (IH)
Sporocyst larvae
Cercaria
Life Cycle of Schistosoma sp.
Comparison of Schistosoma vs. other flukes’ Life Cycle
Trematode Eggs
Types of Parasites
According to Taxonomic Group
Helminths Phylum: Platyhelminthes Elongated, flattened, ribbon-
like worms
Segmented
Hermaphroditic
Reproduction by:
Oviparous Eg. Taenia
Infection by:
Ingestion of encysted larvae Eg. Taenia, Echinococcus
Poutrice Eg. Diphyllobothrium
Class: Cestoda
Sub-groups of CestodesPseudophylidea
Cyclophyllidea
Generalized Pseudophyllidean Life Cycle
Adults in DH SI
Egg
Coracidium
Procercoid larva Copepod First IH
Plerocercoid larva Fish Second IH
Adults in DH SI
Pseudophyllidean (Diphyllobothrium latum) life cycle
Generalized Cyclophyllidean Life Cycle
Adults in DH SI
Egg with Onchosphere/Hexacanth Embryo
Larva (Cysticercoid, cysticercus, coenurus, hydatid) in IH
Adults in DH SI
Taenia species life cycle
Cestode Affecting Man
Species Size Shape ColorStage of Development
When PassedSpecific Features
and Variations
Taenia saginata Taenia solium
35 m. Range, 31-43 m.
Spherical with thick striated shell.
Walnut brown. Embryonated. 6-hooked oncosphere present inside a thick shell.
Thick, striated shell. Eggs of T. solium and T. saginata are indistinguishable and species identification should be made from proglottids or scoleces. "Taenia" spp. should be reported if only eggs are found.
Hymenolepis nana 47 m x 37 m. Range, 40-60 m x 30-50 m.
Oval. Shell consists of 2 distinct membranes. On inner membrane are two small "knobs" or poles from which 4 to 8 filaments arise and spread out between the two membranes.
Colorless, almost transparent.
Embryonated. 6-hooked oncosphere inside shell.
Polar filaments.
Hymenolepis diminuta*
72 m. Range, 70-86 m x 60-80 m.
Round or slightly oval. Striated outer membrane and thin inner membrane with slight poles. Space between membranes may appear smooth or faintly granular.
Yellow. Embryonated. 6-hooked oncosphere inside shell.
Resembles H. nana but lacks polar filaments. Poles are rudimentary and often hard to see.
Dipylidium caninum* 35-40 m. Range, 31-50 m x 27-48 m.
Spherical or oval. 5-15 eggs (or more) are enclosed in a sac or capsule.
Colorless. Embryonated. 6-hooked oncosphere inside shell.
Eggs are contained in a sac or capsule which ranges in size from 58 m to 60 m x 170 m. Occasionally capsules are ruptured and eggs are free.
Diphyllobothrium latum
66 m x 44 m. Range, 58-76 m x 40-51 m.
Oval or ellipsoidal with an inconspicuous operculum at one end and a small "knob" at the other end.
Yellow to brown. Unembryonated. Germinal cell is surrounded by a mass of yolk cells which completely fills inner area of shell. Germinal cell is usually not visible.
Egg resembles hookworm egg but has a thicker shell and an operculum.
* Usually found in lower animals, only occasionally found in humans.
Cestode Eggs
Types of Parasites According to Taxonomic Group
Phylum Arthropoda
4 Morphologic Characteristics:
Segmented body parts: head, thorax and abdomenThree to Four pairs of jointed appendagesCovered by hard chitinous exoskeletonBilaterally symmetrical body
Medical Significance of Arthropods to Man
As direct agents of diseasesDermatitis – due to insect bites ( Caterpillars, bugs, etc)
Injury to sense organs – (wasps and bees )
Infestation of insect larvae - myiasisEntomophobia- fear of insects (eg. Cockroaches)
Envenomization ( Sting of scorpions)
Ectoparasites ( Scabies, Pediculosis and Crab louse infn)
A vectors or disease transmittersMechanical vectorsBiological vectors
Types of Host
VectorMechanical VectorAn invertebrate animal which merely transfer parasitic organism from one host to another by their appendages
Eg. flies, cockroaches
Biological VectorAn invertebrate animal which harbor the parasitic organism internally with further development
Eg. mosquitoes, bugs
Eg. Mosquito in Malaria
Types of Parasites According to Taxonomic Group
Phylum ArthropodaClass Pentastomida eg. Tongue worm
Class Crustacea : crabs, crayfish, copepods
Class Arachnida : spiders, scorpions, ticks, mite
Class Insecta : Order Anoplura : human liceOrder Hemiptera : reduviid bugOrder Diptera : Housefly
Order Hymenoptera : ants, bees, wasps
Order Siphonaptera : fleas
Order Diptera : mosquitoes, flies
Class Chilopoda : centipedesClass Diplopoda: millipedes
Importance of Studying Medical Parasitology
To know the different parasites affecting man
To know how to prevent transmission of these parasitic infections to man
Life Cycle of Ascaris lumbricoides
Habitat:
Small Intestine
Early diagnosis
Cooking food properly
Proper excreta disposal
Prophylactic Treatment of Cases
Mode of Transmission: Ingestion
Early Treatment of Cases
Avoid use of night soil
Proper excreta disposal
Early Treatment of Cases
Types of Parasites
According to their Mode of Transmission and their Preventive
Measures
1. Contact Transmitted2. Soil-transmitted3. Arthropod-transmitted (Vector-
borne)4. Snail-transmitted5. Food/Animal-transmitted6. Water-transmitted
1. Contact Transmitted Infection is
transmissible directly from person to person
Eg. Enterobius vermicularis
Trichomonas vaginalis Sarcoptes scabei Pediculus capitis
Types of ParasitesAccording to their Mode of
Transmission and their Preventive Measures
Preventive measures:Avoid contact with infected individualsImmediate treatment with infecd individuals
2. Soil-transmitted The infective stage
become infective after a period of incubation in the soil.
Eg. Ascaris lumbricoides
Trichuris trichiura Ancylostoma duodenale Necator americanus Strongyloides stercorales
Types of ParasitesAccording to their Mode of
Transmission and their Preventive Measures
Preventive measures:Proper disposal of human fecesAvoid use of night soil as fertilizerProtection of skin from contact with contaminated soil
3. Arthropod-transmitted Infective stage
develops in the arthropod intermediate host which transmits the infection by biting or when ingested by manEg. Plasmodium spp.
Wuchereria Trypanosoma
Types of ParasitesAccording to their Mode of
Transmission and their Preventive Measures
Preventive measures:Destruction of the arthropod breeding placesUse of chemical prophylaxis
4. Snail-transmitted Infective stage
develops in the snail intermediate host or second intermediate host after partial development in the snail
Eg. Schistosoma
Echinostoma
Types of ParasitesAccording to their Mode of
Transmission and their Preventive Measures
Preventive measures:Destruction of snail vectorsAvoid contact with infected or contaminated bodies of waters
5. Food/Animal-transmitted Infective stage develops in
animals whose flesh is an important food item of man
Eg. Trichinella spiralis
Taenia solium Capillaria philippinensis Paragonimus westermani
Types of ParasitesAccording to their Mode of
Transmission and their Preventive Measures
Preventive measures:Proper cooking of food
like meat and fish
6. Water-transmitted Infective stage of the
parasite develops in the external environment and usually reaches man through ingestion of contaminated water.
Eg. Giardia lamblia
Entamoeba histolytica
Types of ParasitesAccording to their Mode of
Transmission and their Preventive Measures
Preventive measures:Boiling of drinking water
1. Contact Transmitted
2. Soil-transmitted3. Arthropod-
transmitted4. Snail-transmitted5. Food/Animal-
transmitted6. Water-
transmitted
Types of ParasitesAccording to their Mode of
Transmission and their Preventive Measures
Preventive measures:
HEALTH EDUCATION
- an essential component of control regardless of the the category of transmission of the parasite belongs to.
Self-Assessment Questions
Given the following parasites, name their respective mode of transmission:
1. Schistosoma spp.2. Trichomonas3. Ascaris4. Giardia5. Capillaria6. Entamoeba7. Taenia solium8. Wuchereria9. Sarcoptes scabei10.Plasmodium
1. Snail-transmitted
2. Contact-transmitted
3. Soil-transmitted
4. Water-transmitted
5. Food- transmitted (fish)
6. Water-transmitted
7. Food-transmitted (pork)
8. Vector-borne
9. Contact-transmitted
10. Vector-borne
Sharing Time
What are the important things that I learned from
this session?
Thank You!
“I will make you wise and show you where to go.
I will guide you and watch over you!”
says the Lord.
Psalm 32:8