www.soran.edu.iq parasitology m. saadatian parasites 1
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Parasites (Lec 2)
•A living organism that have difference types•Evolutionary is not completed •Do not provide their food and other living necessary ( temperature, humidity, …)•For this reason they are associated to other organism (host) and often harmed.
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Parasite types
• Protist (Protozoa)• Worms (Helminths)– Circular worm (Nematoda)– Platyhelminth• tapeworms (Cestoda)• leaf-like (Trematoda)
• (Arthropoda)
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DIFFERENT KINDS OF PARASITESEctoparasite – a parasitic organism that lives on the outer surface of its
host, e.g. lice, ticks, mites etc. 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 nonparasitic modes of living and hence does not absolutely depend on the parasitic way of life, but is capable of adapting to it if placed on a host; e.g. Naegleria fowleri.
Accidental parasite – when a parasite attacks an unnatural host and
survives; e.g. Hymenolepis diminuta (rat tapeworm).
Erratic parasite - is one that wanders in to an organ in which it is not usually found; e.g. Entamoeba histolytica in the liver or lung of humans.
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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)
Paratenic or transport 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 (no parasite development).
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).
Accidental host – a host that is under normal circumstances not infected with the parasite.
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EFFECT OF PARASITES ON THE HOST
The damage which pathogenic parasites produce in the tissues of the host may be
described in the following two ways;
Mechanical injury - may be inflicted by a parasite by means of pressure as it grows
larger, e.g. Hydatid cyst causes blockage of ducts such as blood vessels producing
infraction.
Deleterious effect of toxic substances- in Plasmodium falciparum production of toxic
substances may cause rigors and other symptoms.
Deprivation of nutrients, fluids and metabolites -parasite may produce disease by
competing with the host for nutrients.
Immunological reaction: Tissue damage may be caused by immunological response
of the host, e.g. nephritic syndrome following Plasmodium infections.
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Some terminology to be used Epidemic (disease that affects a large number of humans and spreads
rapidly)
Heteroxenous (alternation of generations of a parasite; altrnative host
life cycle)
Infection (parasitic invasion resulting in injury and reaction to injury)
Monoxenous (single host life cycle)
Parasitemia (parasites in blood)
Pathogenic (results in disease or morbid symptoms)
Prevalence (number of organisms in a population infected with a parasite at any one time)
Virulence (relative infectiousness of a parasite)
Zoonosis (animal diseases that may be transmitted from animals to humans