Parasitology is the area of science which
deals with the study of organisms that lives within the body of another
organism for survival.
Types of relationship:
1. Symbiosis – type of relationship between two
organisms that cannot exist independently, life apart is impossible.
2. Mutualism – type of relationship beneficial
to both the parasite and the host.
3. Commensalism – type of relationship wherein
one is benefited, the other is neither benefited nor harmed.
4. Parasitism – refers to harmful or harmonious
relationship between two organisms:
Classification of parasite
a. Based on habitat
(1)Endoparasite – those found within the body of
the host.
e.g. worms, amoeba
Infection – invasion made by endoparasite
Types of infection:
(a)
Superinfection – when an individual harboring a
parasite is reinfected with the same species of parasite.
(b)Autoinfection – when the infected person in
his own direct source of re–exposure; it may be external (perianal or anus to
mouth via finger or soiled linen) or internal in the mode of transmission.
(2) Ectoparasite – those that
lives on the surface of the body of the host
e.g.
lies, fleas, ticks
Infestation
– invasion made by ectoparasite
b. Based on the effect of parasite
to host
(1) Pathogen –
disease–producing
(2) Non–pathogen
/ Commensals
c. Based on the mode of living
(a) Facultative
– those that can survive even without a host
(b) Obligatory –
those that cannot live without a host.
(c) Permanent – those found within the host from
early life to maturity
(d) Erratic –
parasite that becomes fixed in an unusual organ different from that which it
ordinary parasitized
(e) Intermittent
– those that simply visit the host during feeding time.
(f) Periodic – type of parasite wherein the
larval stage develops in a host different from that of adult.
(g) Transitory
or temporary – type of parasite wherein the larval stage develops in a host
while the adult is free living
(h) Incidental –
one that establishes itself in the host in which it does not ordinary live.
(i) Coprozoic or spurious – species that are
passed thru the alimentary tract without infecting the host at times recovered
in a living or dead stage from human excreta
(j) Saprophytes – that which lives in organic
substances in state of decomposition.
Specificity of parasites:
1. Zooparasites
a. Absolute – highly specific for animals, man
is completely insusceptible.
b. Relative – specific for animals but man may
become susceptible
2. Anthroparasites
a. Absolute – highly specific for men and
animals are not susceptible
b. Relative – specific for man but animals may
become susceptible
3. Anthrozooparasite – equal specificity of
parasite for both man and animals
Related parasitology term
1. Exposure – the act or process of inoculation.
2. Carrier – usually an individual harboring the
parasite but do not show any signs and symptoms; a state wherein the parasite
live in or on the tissues of its host without causing evident harm.
3. Biological incubation – development of
parasite in the particular host; it is usually terminated as soon as the
parasite or their products can be demonstrated in the feces or other excreta or
in the circulating blood (parasetemia), by aspiration, biopsy or other diagnostic
procedure.
4. Clinical incubation – interval between
exposure and the earliest evidence of symptoms produced as a result of
infection or infestation.
5. Zoonosis – literally, disease of animals but
today employed for those diseases of animals which are transmissible to man.
a. Euzoonosis – a type of zoonosis common to man
and reservoir host
b. Parazoonosis – a type of zoonosis in which
man is an infrequent or incidental host.
c. Anthropozoonosis – infection acquired by man
from other vertebrates, e.g., directly, in trichinosis or by large number of
infections transmitted by anthropods and molluscan intermediate host.
6. Zooanthroponoses – diseases primarily of
human origin which may be acquired by other vertebrates.
7. Amphizenoses – disease common to man and
other vertebvrates.
8. Anthroponoses – disease presently restricted
to man which have presumable evolved from other host sources.
9. Pseudoparasite – artifacts mistaken as
parasite.
Distribution of disease
1. Endemic – there is a steady, moderate level
of disease in human population.
2. Hyperendemic – there is a high prevalence of
the disease in a human population.
3. Epidemic – there is a sudden rise in the
incidence or an outbreak of considerable intensity occurs in a disease in human
population.
4. Sporadic – when the disease in human
population appears only occasionally in one or at most a few numbers of a
community.
5. Pandemic – when communicable disease have
been disseminated over an extensive areas of the world.
Sources of exposure:
1. Contaminated soil or water
a. A. lumbricoides
b. T. trichiura
c. Human hookworm
d. S. stercoralis
e. Variable cyst of parasitic amoeba
f. Intestinal flaggelates
g. T. solium ova
h. Infective cercareal stage of the human blood
fluke
2. Food containing the immature
infective stage of the parasite
a. Fresh water fishes: D. latum, liver and
intestinal flukes
b. Crabs & crayfishes: Oriental lung fluke
c. Hog flesh: T. spiralis & T. solium
d. Beef: T. saginata
e. Buffalo nuts: Giant intestinal fluke (F.buski)
f. Water crests: F. hepatica
3. Blood sucking insects transmit
a. Malarial parasites
b. Filarial worms
c. Leishmanias
d. Trypanosomes
e. Viruses
f. Rickettsias
g. Bacteria
h. Spirochetes
4. Domestic or wild animals
harboring the parasite
a. Dogs: hydatid cyste of E. granulosus and T.
carius
b. Herbivorous animals: Trichostrongylus spp.
5. Another person, his clothing,
bedding or immediate environment which he has contaminated
a. E. histolytica
b. E. vermicularis
c. H. nana
6. One’s self: autoinfection with
a. S. stercoralis
b. T. solium
c. E. vermicularis
Portal of entry
1. By mouth
a. Intestinal protozoa (encyted stage)
b. A. lumbricoides
c. T. trichiuria
d. E. vermicularis
e. H. nana
f. Trichostrongylus spp.
g. T. spiralis
h. T. solium
i. D. latum
j. P. westermani
2. Skin penetration
a. Hookworms
b. Stronglyloides
c. Blood flukes
3. Inhalation of eggs
a. E. vermicularis
b. A. lumbricoides
4. Transplacental infection
a. T. gondii
b. Malarial parasite
c. Blood flukes
5. Sexual intercourse
a. Trichomonas vaginalis
Pathogenesis of parasite to host:
1. Traumatic or physical change – when parasite
invades the skin.
2. Lytic necrosis – enzymes elaborated by many
parasites make it possible for them to digest available food in the immediate
environment and to transform this nutrient into their own protoplasm or to
store it for the production of energy; also used as a mean of tissue
penetration.
3. Stimulation of host–tissue reactions – there
is a cellular proliferation and white cells infiltration at the site of the
parasite; these reactions are produced by almost all animal parasite.
4. Toxic and allergic phenomena – when proteins
or other metabolites of the parasites are introduced into the body, there is
sensitization to the foreign substances which may produce hypersensitization to
anaphylactic shock.
5. Opening of pathways for entry of other
pathogens into the tissue – secondary invasions by bacteria
Diagnosis
1. Clinical – the physician obtain information
concerning the effect of parasitic diseases on the basis of the subjective and
objective symptoms evoked, the patient’s history and physical examination.
2. Laboratory – it is important for the
clinician to known what type of specimen should be obtained from the patient
for laboratory analysis, whether stool, blood, urine, sputum, aspirate or
biopsy. It is equally important to know how and when the specimen is to be
obtained and what precautions are to be taken so that it will be satisfactory
for examination.
a. Stool specimens should be free of oil,
particulate minerals (magnesia, kaolin, barium or bismuth), without
contamination of urine and should be placed in a sterile container. They should
be fresh especially if they are diarrheic; if delay in diagnosis is
anticipated, they should be satisfactorily preserved.
b. Blood films should be made on microscope slides
which are absolutely clean and grease–free and sera for immunologic tests
should be obtained aseptically and free of hemolyzed red cells.
Prevention
1. The detection, accurate diagnosis and
evaluation of the clinical importance of the disease in the patient.
2. Adequate treatment of the patient.
3. Search for and treatment of other cases in
the patient’s family.
4. Determination, if possible, of the source of
the infection, reporting it promptly to health officials.
5. Advice to patients and their families as to
how they can avoid further exposure.
6. Support and cooperation in community
preventive measures.
7. Education of patients in ways of utilizing
and strengthening local health departments.
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