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MEDICAL PARASITOLOGY
Bushehr University of Medical Sciences
Department: Microbiology and Parasitology
Module: Medical Parasitology (Introduction)
Instructor: Mohammad Rayani, Ph.D
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.
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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.
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(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
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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.
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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.
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(Parasites) :ه انگل ف انواع كه ائ زنده موجودات داشته مخت
ي درجه نظر از م و بوده پست تكدر مين به ق ت ت ج نيستند (حرارت درجه و ،رطوبت غذا،مسكن) خود زيستي احتي
ن)ديگر موجودات به وابسته منظور اين براي و و هستند (ميزبهی نند صدمه آن به گ .ميرس
انواع انگل ه خته ه (Protozoa)تک ی ک ه( (Helminths ی دپ (Arthropoda) ب
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.
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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).
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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(
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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.
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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.
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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)
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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.
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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
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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).
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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
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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
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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
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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.
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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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