Unit 1 - Introduction
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Lecture 1+2 – Introduction to helminthes
Parasitology
: Is the science that deals with parasites
& their pathogenic effects.
Terms & Terminology of parasitology
Parasite:
Is an organism adapted to live on or in other
organism (host).
Symbiosis
: The relationship between two dissimilar
organisms adapted to living together & lost the ability to
live alone.
Symbiont:
The association may be beneficial or harmful
to either of the associates.
Mutualism
: The relationship which is benefit for both
associates.
Commensalisms
: The relationship between the parasite
& the host, when one of the associated is benefited & the
other (host) neither benefited nor harmed. e.g. E. coli
Bacteria live in human colon but doesn’t cause trouble to
human.
Parasitism
: Where the relationship is harmful to the
host. e.g. E. histolytica.
Ectoparasites
: The organisms (parasite) that live on or
in the skin of their hosts. This relationship called
“infestation”, e.g. Arthropods.
Endoparasites
: The parasites which live inside the
body of the host (in the digestive tract, extraintestinal
organs & tissues, intracellular. This relationship called
“infection”
The parasite have achieved secure ecologic niche
within the host, lost some of its morphological features
and develope d physiological & biochemical adaptati on
needed for its new life.
Obligate parasites
: Parasites that are entirely
dependant on their hosts & cannot live outside the host.
Facultative parasites
: Parasites that are capable of
living either free or in or on a host.
Parasites can be classified by the duration of
their association with their hosts:
Temporary parasite
: Visits a host for a short period.
Permanent parasite
: Leads a parasitic life all through
its life.
Wandering or Aberrant parasite
: Parasite reaches a
place where it cannot live.
Pseudoparasite
: Is an object that resembles a parasite
or the egg of a parasite but it is not a parasite (called
artifact) this is include yeast, hairs, spores……..
Coprozoic or Spurious parasite
: These are the eggs
of some helminthes that are accidental ingested in food &
pass through the intestine & are found in faecal without
causing infection to the host.
Types of hosts:
Is the human & organism which harbors the parasite.
Definitive host:
Is the organism in which the adult or
final stage of the parasite develops or where sexual
reproduction of the parasite occurs. e.g. Schistosoma spp.
Intermediate host:
The organism (host) which harbors
the larval (a sexual stage) develops. Some have two
intermediate hosts.
Paratenic host:
Is the host in which the parasite is
transported & neither gains nor loses infectivity for its
definitive host. Or A carrier or transport host where the
parasite remains viable without further development
Reservoir host
: Is an animal species on which the
parasite depends for its survival in nature & acts as a
source of infection for other hosts including man. e.g.
cutaneous Leishmania & its reservoir host is the dog.
Vector:
Is the transmitter of parasites from host to host .
(Agents of transmission).
It is essential for the parasite life cycle called
“biological vector” e.g. Anopheles female which is
the vector of the plasmodium parasite (so it is a
definitive host & biological vector) e.g. Sand fly.
When the vector is not essential for the parasite life
cycle, It is called “Mechanical vector” e.g. E.
histolytica transmitted by the house fly which is a
vector of it but it may be transmitted by other hosts.
Zoonosis
: It is a term applies to the disease which
transmitted from animal to human either incidentally or
commonly.
Classification of animal parasites & vector:
Four groups are of major importance in medical
parasitology:
1) Protozoa 2) Helminths 3) Molluscs 4) Arthropods
According to the zoological nomenclature within the
animal Kingdom we have:
Phylum, Subphylum,…………….larger division
Classes, Orders, Families, Genus & Species ……
Lesser division
All these names must be of Greek or Latin origin.
Species: Designates a population having the same genetic
characters & are capable of continued reproduction of
their kind & can not interbreed with other species.
Unit 1 - Introduction
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Genus: Is a group of closely related species.
The scientific name consist of generic name with initial
capital letter & specific name with initial small letter.
Pathogenesis and symptomatology:
Parasites that injury the host are Pathogens.
The development of the damage called Pathogenesis.
Degree of injury depends on several factors:
1) Potential virulence of the agent (i.e. its intrinsic
pathogenecity).
2) A mount of inoculum & rapidity of multiplication.
3) The site of inculation.
4) Exposure is single or repeated.
5) Resistance or tolerance of the host to particular strain
of agent.
6) General resistance of the host.
7) Type of damage caused by agent, which either:
Mechanical, Lytic, Toxic & Allergic
Symptoms
:
Are the manifestations of pathological
process result from the effect of the agent.
Host response
: The reaction of the host has distinct
bearing on immediate or sub sequent effect of
pathogens.
In some cases the host unresponsive, but in other may
produce Ab. to counteract the agent Ag produced by
pathogens or may wall of the invader or its products
by cellular infiltration or proliferation.
The host response may be local at the site of injury or
systemic including cellular or humeral changes.
Diagnosis:
Diagnosis of parasitic diseases depends on 2 parts:
1) 1
st.
Clinical features: like fever, pain
2) 2
nd.
Laborator y diagnosis to:
a) Detect the presence of eggs, larvae, cysts (in stool,
urine, blood sputum).
b) Distinguished these stages from each other.
c) Find out whether it is the causative agent or
coincidental.
Epidemiology:
Is the science concerned with factors which determine the
prevalence of infection & incidence of disease.
It is the history of the disease including not only infection
in man but also in animals, and agents that serve as
reservoir & vectors.
Prevalence:
Is define as the number of infected
individuals at a given time in a designated area.
Incidence:
Is the rate or frequency with which a disease
(new infection) occurs.
Infections maintained at a more or less stable rate of
prevalence within the human population of an area are
said to be Endemic, but in high prevalence called hyper
endemic. If it appears irregularly in scattered individuals
it Sporadic. If it appears in high prevalence in unusual
transmission it is Epidemic.
All these terms are special for human. For animals called
(Enzootic, hyper enzootic, Epizootic & Sporadic).
Parasitic disease may be grouped epidemiologically
as follows:
1) Filth-borne or contaminati ve :
Like intestinal protozoa, helminthes, louse infestation.
2) Contracted from soil or water:
Like eggs of Ascaris &Trichuris, or through the skin as
with the infective larvae of hook worms or blood flukes.
3) Food-bor ne infections:
Like Taenia spp. Eating raw or under cooked meat
containing the larval stage of the parasite.
Also ingestion of encysted larvae on aquatic plants.
4) Arthropods-bor ne infection:
Like Malaria- Leishmania
Arthropods essential intermediate host & vector.
5) Infestation by arthropods:
Like the Lice.
6) Arthropod envenomation:
Like the bite of Scorpion.
Mode of infection:
The means by which the different infecting agents are
transmitted from the host to another. e.g. The
Plasmodium reach human through injection by the
Anopheles female.
The avenues where they enter the human body called
(portal of entery).
Control & Prevention:
Parasitic diseases involve the individual & community in
which he lives, therefore measures should be taken for
these entities.
The individual: In the parasitized individual….
Chemotherapy should be used not only to relieve suffering but
also to prevent transmission to new host in the community.
Medical education in methods of personal hygiene &
provision of means for taking precautions against exposure.