Introduction in human Parasitology

8/12/2019 Introduction in human Parasitology

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Introduction in medical parasitology

and parasitic diseases


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Medical (human) parasitology

Human parasitology is the study of those organisms

which parasitise humans

According to the very broad definition of parasitology,

parasites should include the viruses, bacteria, fungi,

protozoa and metazoa(multi-celled organisms) which

infect their host species

However, for historical and other reasons the first threehave been incorporated into the discipline of Microbiology


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Medical parasitology has toinvestigate all aspects of

the following:

The biology of the parasite

The variation in life-cycle of the parasites

Methods of invasion of the host

Migration and maturation within the host

The effect of the parasite upon the host

The host reaction and response to the

parasite

Methods of escape from the host

istribution of the parasite

iagnosis of parasitic diseases

Treatment and prevention of the diseases

Agent s of diseases

!pidemiology

"athogenesis and basicclinical signs

#aboratory diagnosis

Antiparasitic drugs

"revention


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"arasitic diseases$factors that led to the increasing fre%uency of some

parasitic diseases and their spread

Increased mobility of the population

"opularity of the tropics and subtropics as vacation areas

&peed of transportation

'efugees from war-torn areas

Modification of environment by humans

lobal warming*

Illegal trade of animals

AI& and patients under immunosuppression

evelopment of resistance to drugs (antimalarials)


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eographic distribution factors(endemicity)

"resence of a suitable host

Habits of the host

!scape from the host

+avorable conditions outside of host

!conomic and social conditions


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Geographic distribution of malaria


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Chloroquine resistance in malaria


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Geographic distribution of Echinococcusgranulosus


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H . "riority diseases

&chistosomiasisMalaria+ilariasis

Trypanosomiasis#eishmaniasis

#eprosy (replaced byHI/0AI&)

#ymphatic filariasis

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The burden of some ma4or parasitic infections

Parasite Diseases o! people infected Deaths"yr

Plasmodium malaria 567 million 8985 million

&oil transmittedhelminths:

'oundworm(Ascaris)

hipworm(Trichuris)

Hoo2worm

(AncylostomaandNecator)

"nemonitis, intestinalobstruction

;loody diarrhoea,rectal prolapse

1oughing, whee


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!pidemiology

Although parasitic infections occur globally, the

ma4ority occur in tropical regions, where there is

poverty, poor sanitation and personal hygiene

ften entire communities may be infected with

multiple, different organisms which remain

untreated because treatment is neither accessible

nor affordable

!ffective prevention and control re%uires Cmass

intervention strategies* and intense community

education9 !3amples include:

eneral improved sanitation: pit latrines, fresh

water wells, piped water

/ector control: insecticide impregnated bed

nets, spraying of houses with residual

insecticides, drainage, landfill

Mass screening and drug administration

programmes which may need to be repeated

at regular intervals


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Three of life - Ta3onomy


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Dey definitions

#u$aryote:a cell with a well-definedchromosome in a membrane-bound nucleusBall parasitic organisms are eu2aryotes

Protozoa:unicellular organisms, e9g9Plasmodium(malaria)

Metazoa:multicellular organisms, e9g9helminths (worms) and arthropods (tic2s, lice)


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!3ample:The present classification scheme of protists, based largely on theirgenetic relatedness

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!3ample: The traditional classification scheme of protists, based largely on morphological characteristics and it is no longer valid

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;iological associations

%ymbiosis

Two different organisms live together and

interact

In this association one partner lives in oron another oneEs body

&ymbiosis include 7 types of associations:mutualism, commensalism,

parasitism


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Mutualism

"ermanent association between two differentorganisms that life apart is impossible, twopartners benefit each other, such as termites andflagellates

The mutuals are metabolically dependent on one

anotherB one can not survive in the absence ofthe other


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1ommensalism

The association of two differentorganisms, in which one partner is benefitedwhile the other neither benefited nor in4ured,such as Entamoeba coli and man9


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"arasites and parasitism

P&'&%()#- live orgamism living in or on, and

having some metabolic dependence on another

organism 2nown as a host

P&'&%()(%M- a relationship in which one of the

participants, the parasite, either harms its host orin some sense lives at the e3pense of the host


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"arasites

Protists *protozoa+: Sarcomastigophora, Ciliophora,

Apicomplexa

orms:Aschelminthes , Platyhelminthes

&rthropods:Arthropoda

Microsporidia !icrospora 0ta3onomy unclearF

Nematoda(roundworms), Cestoda(tapeworms),Trematoda(flu2es)


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-uman

Parasitology

Medical

Helminthology

Medical

Protozoology

Medical

Entomology


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"arasites

Microparasites 0 Macroparasites

!ndoparasites 0 !ctoparasites

Intracellular parasites (mostly microscopic)

!3tracellular parasites (they range in si


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"arasites

G .bligate *permanent+ parasites . organisms that for

all or most of their life cycle are parasiticB they have atleast one host during their life-history

G )emporary *intermittent+ parasites . agents that areparasitic for limited periods for either feeding or

reproduction

G /acultative parasites . organisms that are notnormally parasitic but can survive for a limited periodwhen they accidentally find themselves within anotherorganism

G &daptive parasites . those organisms that havecapacity to live both as free-living or parasitic organisms


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#ife cycle

#ife cycle is the process of a parasiteEsgrowth, development and reproduction,

which proceeds in one or moredifferent hosts depending on thespecies of parasites

(nfective stage is a stage when aparasite can invade human body and livein it


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#ife cycle

(nfective route is the specific entrancethrough which the parasite invades thehuman body

(nfective mode means how theparasite invades human body, such as:

89 the cercariae of the blood flu2e activelypenetrate the s2in of a swimming man

59 the infective Ascaris eggs are swallowed byman


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#ife cycles

Direct life cycle

only a single host in the

life cycle

Indirect life cycle

life cycle with more than one host

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-ost

-ost - in parasitism, it supplies theparasite with nourishment and shelter, it is

the in4ured partner

Carrier - a person who harbours parasite,has no clinical symptoms, is an importantsource of infection in epidemiology


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Hosts

Definitive host- one in which the parasite reaches se3ual maturity

and where the adult form of the parasite usually resides or in which

se3ual stages of reproduction occur

(ntermediate host- one in which the immature or larval form

usually resides, or in which the parasite undergoes ase3ualreproduction

)ransport (paratenic)host- one in which the parasite does not

undergo any development but in which it remains alive and infective

to another host

'eservoir host- any animal that harbors an infection that can be

transmitted to humans, even if the animal is a normal host of the

parasite


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Host specificity

hich hosts can be infected by givenparasite0

Many parasites have very specifiedhost

Ascaris lumbricoides

thers have wide range of hosts Toxoplasma gondii


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!pidemiology

1oonosis

disease which is the result of the transmission ofparasites normally found in wild and0or domesticanimals to humans (these animals infected withparasites are called reservoir hosts)

%ylvatic cycle

2rban *domestic+ cycle

&heeps arereservoir hostfor liver flu2e

Fasciolahepatica

e9g9 Trichinellaspiralis


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!pidemiology

Methods of infection faeco-oral (Entamoeba histolytica, Ascaris lumbricoides)

undercoo2ed food (Trichinella spiralis)

via arthropod vector (malaria)

direct penetration (Strongyloides stercoralis,Ancylostoma duodenale)

direct contact 0person to person (Trichomonas "aginalis,Sarcoptes scabiei)

Methods of ecsape

faeces

sputum

via arthropods


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Method of infection$arthropods: biological transmission

"athogens have to spend a

part of their life cycle in the

vector arthropods in which

they multiply or develop

into the infective stage and

then invade the human

body under the help of the

arthropod

!9g9 Anopheles mos%uitoes

transmit malaria

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Method of infection$arthropods: mechanical transmission

Arthropods play a role ofthe transportation of

pathogens, which is notindispensable for thedisease transmission

!9g9 flies carry bacteria,

viruses, wormEs eggs,and amoebic cysts ontheir legs and body

Musca domestica

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"athogenicity

Pathogenicity- pathogenic parasites facultative pathogenicparasites nonpathogenic parasites

(comensals) free-living parasites

.pportunistic parasites- parasites that causemild to moderately serious infections in healthy

individuals, but particularly serious infections inthe immunocompromised host


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"athogenic effects of parasites

)rauma - destruction of cells, tissues or organs bymechanical or chemical means

utrition robbing - diversion of the hosts nutritivesubstances (e9g9 hoo2worms suc2 blood)

)o3in production

(nteractions of the host immune"inflammatoryresponses (pathology due to host response -

immunopathology)

Hoo2wormanemia


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Immune effector mechanisms

P

&'&%()

#

C.MP4#M#)

&)(5.D(#%

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TcTh8 Th

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Agpresentation


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Preimunition

Its intensity and specificity are usually at a lowerlevel than those produced by bacteria and viruses

It refers to non6sterilizing immunity: the hostmay be protected from superinfection long as the

parasites remain in the body

This situation is 2nown as premunition orconcominant immunity: this may be of greatimportance in endemic areas in limiting the severityof infection with, e9g9 Plasmodium, Schistosoma,hoo2worms and other parasites


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isease

Asymptomatic infection

&ymptomatic infection - acute 0chronic

#atent infection 0Toxoplasma gondii

Malignant alteration 0Clonorchis sinensis,Schistosoma

haematobium


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"arasites$ according to which site they inhabit

(ntestinal and urogenital parasites

(proto


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iagnosis of parasitic infections

1linical diagnosis

#aboratory diagnosis


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Treatment of parasitic infections

Medical and surgical

1hemotherapy

Ade%uate nutrition


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"revention and control

'eduction in sources

!ducation

estruction and0or control of reservoir

hosts and vector


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"roto


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Ta3onomic classification of proto


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+orms and reproduction of proto


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Protozoa

5lood and tissueprotozoa

(e9g99 Plasmodiumspp9)

(ntestinal andurogenital

protozoa(e9g9 Entamoeba

histolytica,Cryptosporidiumspp9)

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Helminths (orms)

!u2aryotic, multicellular animals thatusually have digestive, circulatory,nervous, e3cretory, and reproductivesystems9

orms have bilateral symmetry, head andtail end of the body, and tissue

differentiation (endoderm, mesoderm, andectoderm)9


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Helminthes

)wo main groups *phyla+

"latyhelminths (+latworms)

?ematoda ('oundworms)

4ife Cycle !3tremely comple3 (egg $ larva $ adult)

Intermediate hosts harbor larval (developmental) stage9

efinitive host harbors adult stage

4ocalization

Intestinal helminths

;lood and tissue helmints


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Ta3onomic classification of helminths

Sub

kingdom

Phylum Class Genus examples

Metazoa ematodes$ound %orms& appear round incross section' they have bodycavities' a straight alimentarycanal and an anus

scaris (round%orm)

*richuris (%hip%orm)

ncylostoma (hoo+%orm)

,ecator (hoo+%orm)

Enterobius (pin%orm orthread%orm)

Strongyloides

Platyhelminthes

lat %orms& dorsoventrallyflattened' no body cavity and' ifpresent' the alimentary canal isblind ending

"estodesdult tape%orms are found in theintestine of their host

*hey have a head (scole!) %ithsuc+ing organs' a segmentedbody but no alimentary canal

Each body segment is

hermaphrodite

*aenia (tape%orm)

*rematodes,on-segmented' usually leaf-shaped' %ith t%o suc+ers but nodistinct head

*hey have an alimentary canaland are usually hermaphroditeand leaf shaped

Schistosomes are the e!ception.

asciolopsis(liver flu+e)

Schistosoma (not leafshaped/)


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Helminths

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&e3ual reproduction strategies

Male and female reproductive organs are found in separate individuals9

ne animal has both male and female se3 organs (most hermaphrodites copulate

with other animals, a few copulate with themselves)9

/emale helminths:

.viparous. lay eggs without embryonic development9

.voviviparous. embryos develop inside eggs9

7iviparous . the larva develops inside the body of the mother9

#ggs:unsegmented (no larva inside the egg) J segmented (larva inside

the egg)

8

5

" i l


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"arasite prevalence

e have a parasite problem right here in the&erbia (and other countries)9

It is 4ust not being addressed9

Many doctors haven8t been trained to loo2for parasites, so they don8t find them9

ot li$e to tal$ about these things9

eglected diseases9

Introduction in human Parasitology

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