medical parasitologymed.bpums.ac.ir/uploadedfiles/coursefiles/2_کلیات...introduction to...

MEDICAL PARASITOLOGY

Bushehr University of Medical Sciences

Department: Microbiology and Parasitology

Module: Medical Parasitology (Introduction)

Instructor: Mohammad Rayani, Ph.D

Protozoa

Cyst Trophozoite

Helminths

Egg Larvae Worm

2

Nematodes

Cestodes

Trematodes 3

Introduction to parasitology

Parasitology is a type of SYMBIOSIS (living together)

Man and other living things on earth live in an entangling relationship

with each other; interdependent.

(Any plant, animal, or protist that is intimately

associated with another organism of a different species;

each member is termed a SYMBIONT).

Commensalism, Mutualism and Parasitism are

various type of symbiosis.

4 Dr. M. Rayani (Bushehr University of Medical Sciences)

COMMENSALISM

(when one symbiont, the COMMENSAL, benefits and the

other animal is neither helped nor harmed.

An association in which the commensal takes the benefit

without causing injury to the host.

E.g. most of the normal floras of the humans’ body can be

considered as commensals.


(each member, a MUTUALIST, depends upon the other;

oblilgatory or facultative) many examples in nature.

An association in which both partners are metabolically

dependent upon each other and one cannot live without the

help of the other; however, none of the partners suffers any

harm from the association.

For instance, flagellates produce cellulase in gut of

termites; ciliates in ruminants.

MUTUALISM


PARASITISM

(where one member, the PARASITE, lives in or on another

organism, the HOST)

An association where one of the partners is harmed and the

other lives at the expense of the other.

A parasite is a living organism, which takes its

nourishment and other needs from a host;

The host is an organism which supports the parasite.

E.g. worms like Ascaris lumbricoides reside in the

gastrointestinal tract of man, and feed on important items

of intestinal food causing various illnesses.


Parasitology is the study of the relationship between a

parasite and its host.

Medical parasitology is the science that deals with

organisms living in the human body (the host) and the

medical significance of this host-parasite relationship.

In medical parasitology we will focus on most of the

disease causing (pathogenic) parasites.

The parasites included in medical parasitology are

protozoa, helminths, and some arthropods.


9

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Dr. M. Rayani (Bushehr University of Medical Sciences)

DIFFERENT KINDS OF PARASITES

Ectoparasite – a parasitic organism that lives on the outer surface of its

host, e.g. lice, ticks, mites. Appropriate terminology includes the terms

"infected" and "infested").

Endoparasites – parasites that live inside the body of their host, e.g.

Entamoeba histolytica. Appropriate terminology is "infected;

roundworms in gut.

Obligate Parasite - This parasite is completely dependent on the host

during a segment or all of its life cycle; e.g. Plasmodium spp.

Facultative parasite – an organism that exhibits both parasitic and non-

parasitic modes of living and hence does not absolutely depend on the

parasitic way of life; e.g. Naegleria fowleri.


DIFFERENT KINDS OF HOSTS

Definitive or final host – a host that harbors a parasite in the adult stage

or where the parasite undergoes a sexual method of reproduction.

(parasite reaches sexual maturity and reproduces).

Intermediate host - harbors the larval stages of the parasite or an asexual

cycle of development takes place. (some development in host, but does not

reach sexual maturity; often asexual stages).

Reservoir host – a host that makes the parasite available for the

transmission to another host and is usually not affected by the infection.

(non-human animals that serve as sources of infection to humans).


Typical ways parasites transmitted:

INGESTION from food or water / inhalation

DIRECT PENETRATION of skin from environment

VECTORS (transmits parasites from host to host)

BIOLOGICAL

(essential in life-cycle of parasite)

MECHANICAL

(unessential in life-cycle of parasite(

Dr. M. Rayani (Bushehr University of Medical Sciences) 12

BASIC CONCEPTS IN MEDICAL PARASITOLOGY

In medical parasitology, each of the medically important

parasites are discussed under the standard subheadings of

morphology, life cycle/means of infection, pathology/clinical

manifestations of infection, laboratory diagnosis, treatment,

geographical distribution/epidemiology, preventive/control

measures of parasites.


MORPHOLOGY Includes size, shape, color and position of different

organelles in different parasites at various stages of their development.

A parasite’s LIFE CYCLE consists of two common phases:

One phase involves the route a parasite follows inside the body. This

information provides an understanding of the symptomatology and

pathology of the parasite. In addition the method of diagnosis and

selection of appropriate medication may also be determined.

The other phase, the route a parasite follows outside of the body,

provides crucial information pertinent to epidemiology, prevention, and

control.


LABORATORY DIAGNOSIS

Depending on the nature of the parasitic infections, the

following specimens are selected for laboratory diagnosis:

a) Blood (malaria)

B) Stool (Giardiasis)

c) Urine (Schistosoma haematobium)

d) Sputum (Paragonimus westermani)

e) Biopsy material (kala-azar)

f) Urethral or vaginal discharge (Trichomonas vaginalis)


Treatment

Many parasitic infections can be cured by specific

chemotherapy.

To obtain maximum parasiticidal effect, it is desirable that

the drugs administered should not be absorbed and the

drugs should also have minimum toxic effect on the host.


GEOGRAPHICAL DISTRIBUTION

Although there is a much stronger association with the level of housing,

nutrition, sanitation and general public health than climate; many of

parasitic diseases are still found in abundance in the tropics.

Distribution of parasites depends upon:

a. The presence of a suitable host and food habits

• Host specificity, for example, Ancylostoma duodenale requires man as

a host.

• Food habits, e.g. consumption of raw or undercooked meat or

vegetables predisposes to Taeniasis.

b. Environmental conditions- favoring survival outside the body of the

host, i.e. temperature, the presence of water, humidity etc.

c. Easy escape of the parasite from the

d. The presence of an appropriate vector or intermediate host


PREVENTION

Preventive measures designed against every parasite

infectiving humans to break the transmission cycle.

Such measures include:

Reduction of the source of infection-

A prompt diagnosis and treatment of parasitic diseases is

an important component in the prevention of

dissemination. (The parasite is attacked within the host, thereby

preventing the dissemination of the infecting agent).


Sanitary control of drinking water and food.

Proper waste disposal – through establishing safe sewage

systems, use of screened latrines, and treatment of night

soil.

The use of insecticides and other chemicals used to control

the vector population.

Protective clothing that would prevent vectors from

resting in the surface of the body and inoculate pathogens

during their blood meal.

Good personal hygiene.

Avoidance of unprotected sexual practices.

PREVENTION


NOMENCLATURE

Describing animal parasites follow certain rules of

zoological nomenclature and each phylum may be further

subdivided as follows:

Phylum Subphylum Class Order

Family Genus Species


Medical Protozoology

Deals with the study of medically important protozoa (the

microscopic single-celled eukaroytes).

Medical Helminthology

Deals with the study of helminths (worms- macroscopic,

multicellular worms possessing well differentiated tissues and

complex organs) that affect man.

Medical Entomology

Deals with the study of arthropods which cause or transmit

disease to man.

CLASSIFICATION OF MEDICAL PARASITOLOGY


PROTOZOAN parasites consist of a single "cell-like unit"

which is morphologically and functionally complete and

can perform all functions of life.

They are made up of a mass of protoplasm differentiated

into cytoplasm and nucleoplasm.

The protozoal parasite possesses the property of being

transformed from an active (trophozoite) to an inactive

stage (cyst). The cyst is the resistant stage of the parasite

and is also infective to the human host.

The HELIMINTHIC parasites are multicellular and well

developed organ systems.


1) Brown & Neva. Basic Clinical Parasitology

2) Markell & Voge. Medical Parasitology

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http://dpd.cdc.gov/dpdx/Default.htm

http://www.who.int/tdr/diseases-topics/en/

References:


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