parasitology lec intro

7/25/2019 Parasitology Lec Intro

1/37

Ruel C. Maddawin, RMT

MedicalParasitology


2/37

*A parasite is a living organism, which takes

its nourishment and other needs from a

host; the hostis an organism which supportsthe parasite.

*The parasites included in medical

parasitology are protozoa, helminthes, andsomearthropods.

*The hosts vary depending on whether they

harbor the various stages in parasiticdevelopment.


3/37

Kinds of Parasites

*Ectoparasite a parasitic organism that lives on

the outer surface of its host, e.g. lice, ticks, mites

etc.*Endoparasites parasites that live inside the

body of their host, e.g. Entamoeba histolytica.

*Obligate Parasite This parasite is completely

dependent on the host during a segment or all ofits life cycle, e.g. !lasmodium spp.


4/37

ectoparasitism


5/37

Kinds of Parasites

*Facultative parasite an organism that e"hibits

both parasitic and nonparasitic modes of living and

hence does not absolutely depend on the parasiticway of life, but is capable of adapting to it if

placed on a host. #.g. Naegleria fowleri

*Accidental parasite when a parasite attacks an

unnatural host and survives. #.g. Hymenolepisdiminuta $rat tapeworm%.

*Erratic parasite is one that wanders in to an

organ in which it is not usually found. #.g.

Entamoeba histolytica in the liver or lung ofhumans.


6/37

!ypes of "osts

*#efinitive host a host that harbors a parasite in

the adult stage or where the parasite undergoes a

se"ual method of reproduction.*$ntermediate host harbors the larval stages of

the parasite or an ase"ual cycle of development

takes place. &n some cases, larval development is

completed in two different intermediate hosts,referred to as first and second intermediate hosts.

*Paratenic host a host that serves as a temporary

refuge and vehicle for reaching an obligatory host,

usually the definitive host, i.e. it is not necessary

for the completion of the parasites life cycle.


7/37"osts

*%eservoir host a host that makes the parasite

available for the transmission to another host and

is usually not affected by the infection.

*&atural host a host that is naturally infected

with certain species of parasite.

*Accidental host a host that is under normal

circumstances not infected with the parasite.


8/37

"elminth eggs


9/37'ymbiosis

*There is a dynamic e'uilibrium which e"ists in the

interaction of organisms.

*(ny organism that spends a portion or all of its life

cycle intimately associated with another organism

of a different species is considered as 'ymbiont

$symbiote% and this relationship is called symbiosis$symbiotic relationships%.


10/37( types of symbiosis

)*Mutualism an association in which bothpartners are metabolically dependent upon each

other and one cannot live without the help of theother; however, none of the partners suffers any

harm from the association. E*g* cellulase

producing proto)oans inside termites.

+*ommensalism an association in which thecommensal takes the benefit without causing

in*ury to the host. E*g* Most of the normal floras

of the humans+ body can be considered as

commensals.


11/37

-arnacles on .halesommensalism


12/37( types of symbiosis

*Parasitism an association where one of the

partners is harmed and the other lives at the

e"pense of the other. E*g* orms likeAscarislumbricoides reside in the gastrointestinal tract of

man, and feed on important items of intestinal

food causing various illnesses.


13/37

Parasitism


14/37EFFE! OF PA%A'$!E' O& !"E "O'!

*The damage which pathogenic parasites produce in

the tissues of the host may be described in the

following two ways-)* #irect effects of the parasite on the host+* $ndirect effects of the parasite on the host


15/37#irect effect

*Mechanical in/ury may be inflicted by a parasite

by means of pressure as it grows larger, e.g.

ydatid cyst causes blockage of ducts such asblood vessels producing infraction.

*#eleterious effect of to0ic substances in

Plasmodium falciparum production of to"icsubstances may cause rigors and other symptoms.

*#eprivation of nutrients, fluids and metabolitesparasite may produce disease by competing with

the host for nutrients.


16/37$ndirect effect

*$mmunological reaction1 Tissue damage may be

caused by immunological response of the host, e.g.

nephritic syndrome following !lasmodiuminfections.

*E0cessive proliferation of certain tissues due to

invasion by some parasites can also cause tissuedamage in man, e.g. fibrosis of liver after

deposition of the ova of /chistosoma.


17/37

'chistosomiasis


18/37-asic oncepts

*&n medical parasitology, each of the medically

important parasites are discussed under the

standard subheadings of morphology, geographical

distribution, means of infection, life cycle,

host0parasite relationship, pathology and clinical

manifestations of infection, laboratory diagnosis,

treatment and preventive0control measures ofparasites.


19/37-asic oncepts

A* Morphology includes si)e, shape, color and

position of different organelles in different

parasites at various stages of their development.

This is especially important in laboratory diagnosis

which helps to identify the different stages of

development and differentiate between pathogenic

and commensal organisms.

*1or e"ample, Entamoeba histolytica and

Entamoeba coli.


20/37

2. 2eographical distribution #ven though

revolutionary advances in transportation has made

geographical isolation no longer a protection against

many of the parasitic diseases, many of them are

still found in abundance in the tropics. 3istribution

of parasites depends upon-

a% The presence and food habits of a suitable hostb% #asy escape of the parasite from the host

c% #nvironmental conditions favoring survivaloutside the body of the hostd% The presence of an appropriate vector or

intermediate host


21/37-asic oncepts

* 3ife cycle of parasites the route followed by a

parasite from the time of entry to the host to e"it,

including the e"tracorporeal $outside the host% life.

&t can either be simple, when only one host is

involved, or comple", involving one or more

intermediate hosts.


22/37-asic oncepts

#* "ost parasite relationship infection is the

result of entry and development within the body of

any in*urious organism regardless of its si)e. 4nce

the infecting organism is introduced into the body

of the host, it reacts in different ways and this

could result in-

a* arrier state a perfect host parasiterelationship where tissue destruction by a parasite

is balanced with the host+s tissue repair. (t this

point the parasite and the host live harmoniously,

i.e. they are at e'uilibrium.


23/37-asic oncepts

b* #isease state this is due to an imperfect host

parasite relationship where the parasite dominates

the upper hand. &t can result either from lower

resistance of the host or a higher pathogenecity of

the parasite.

c* Parasite destruction occurs when the hosttakes the upper hand.


24/373aboratory diagnosis

*3aboratory diagnosis depending on the nature of

the parasitic infections, the following specimens

are selected for laboratory diagnosis-

a% -lood in those parasitic infections where the

parasite itself in any stage of its development

circulates in the blood stream, e"amination ofblood film forms one of the main procedures for

specific diagnosis.



b% 'tool e"amination of the stool forms an

important part in the diagnosis of intestinal

parasitic infections and also for those helminthic

parasites that locali)e in the biliary tract and

discharge their eggs into the intestine.

c% 4rine when the parasite locali)es in the urinarytract, e"amination of the urine will be of help in

establishing the parasitological diagnosis.



d% 'putum e"amination of the sputum is useful in

the following-

5 &n cases where the habitat of the parasite isin the respiratory tract, as in !aragonimiasis, the

eggs of Paragonimus westermani are found.

5 &n amoebic abscess of lung or in the case of

amoebic liver abscess bursting into the lungs, thetropho)oites of E. histolytica are detected in

the sputum.



e% -iopsy material varies with different parasitic

infections. 1or e"ample spleen punctures in cases of

kalaa)ar, muscle biopsy in cases of Cysticercosis,

Trichinelliasis, and Chagas+ disease, /kin snip for

4nchocerciasis.

f% 4rethral or vaginal discharge for Trichomonasvaginalis


28/37

!* vaginalis



*&ndirect evidences changes indicative of

intestinal parasitic infections are-

a* Cytological changes in the blood eosiniphiliaoften gives an indication of tissue invasion by

helminthes, a reduction in white blood cell count is

an indication of kalaa)ar, and anemia is a featureof hookworm infestation and malaria.



b* Serological tests are carried out only inlaboratories where special antigens are available.


31/37!reatment

*Many parasitic infections can be cured by specific

chemotherapy.

*The greatest advances have been made in the

treatment of proto)oal diseases.

*1or the treatment of intestinal helminthiasis,

drugs are given orally for direct action on the

helminthes


32/37Prevention and control

*Measures may be taken against every parasite

infectiving humans. !reventive measures designed

to break the transmission cycle are crucial to

successful parasitic eradication.

/uch measures include-

a* %eduction of the source of infection theparasite is attacked within the host, thereby

preventing the dissemination of the infecting agent.



b* 'anitary control of drin5ing .ater and food*

c* Proper .aste disposal through establishing safesewage systems, use of screened latrines, and

treatment of night soil.

d* !he use of insecticides and other chemicals

used to control the vector population*



e* Protective clothing that would prevent vectors

from resting in the surface of the body and

inoculate pathogens during their blood meal.

f* 2ood personal hygiene*

g* Avoidance of unprotected se0ual practices*


35/37

3A''$F$A!$O& OF ME#$A3

PA%A'$!O3O261

a* Medical Protozoology 3eals with the study ofmedically important proto)oa.

b* Medical "elminthology 3eals with the study ofhelminthes $worms% that affect man.c* Medical Entomology 3eals with the study of

arthropods which cause or transmit disease to

man.

6 (n organism which supports a parasite is called a


36/37

6. (n organism which supports a parasite is called a7777777777777.

8 9 the : ma*or classifications of parasitic organisms

that we study in medical parasitology are

. ( parasite that wanders in to an organ in which it is not

usually found is called

?. ( type of host that harbors a parasite in the adult stage

or where the parasite undergoes a se"ual method

of reproduction.

@. a host that is naturally infected with certain species of

parasite.

6A. an association where one of the partners is harmed

and the other lives at the e"pense of the other.


37/37

6. ost8. !roto)oans:. elminths

9. (rthropods. #rratic

?. 3efinitive@. Batural6A.parasitism

parasitology lec intro

Documents