Intro to Parasitology 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



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


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


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


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


Types of Parasites


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


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


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


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


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


Prophylactic Treatment of Cases

Mode of Transmission: Ingestion


Avoid use of night soil



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



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



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



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



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



Preventive measures:Boiling of drinking water

1. Contact Transmitted

2. Soil-transmitted3. Arthropod-

transmitted4. Snail-transmitted5. Food/Animal-

transmitted6. Water-

transmitted



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

Documents

Intro to Parasitology 2010