Intro to Parasitology (Day 1 Lecture) Flashcards
the science that deals with organisms living in the human body (the host) and the medical significance of this host-parasite relationship.
Medical Parasitology
living organism, which takes its nourishment and other needs from a host; the host is an organism which supports the parasite.
Parasite
vary depending on whether they harbor the various stages in parasitic development.
Hosts
Different kinds of parasites:
- Ectoparasite
- Endoparasite
- Obligate parasite
- Facultative parasite
- Accidental parasite
- Erratic parasite
- Non-pathogenic parasites
- Pathogenic parasite
a parasitic organism that lives on the outer surface of its host
Ectoparasite
Examples of ectoparasite
lice, ticks, mites, etc
parasites that live inside the body of their host
Endoparasite
Example of Endoparasite:
Entamoeba histolytica
This parasite is completely dependent on the host during a segment or all of its life cycle
Obligate parasite
Example of ObligateParasite:
Plasmodium spp.
an organism that exhibits both parasitic and non parasitic 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.
Facultative Parasite
Example of Facultative Parasite
Naegleria fowleri
when a parasite attacks an unnatural host and survives
Accidental Parasite
Example of Accidental Parasite:
Hymenolepis diminuta (rat tapeworm)
is one that wanders in to an organ in which it is not usually found.
Erratic Parasite
Example of Erratic Parasite
Entamoeba histtolytica in the liver or lung of humans
parasite that do not cause disease
Non-Pathogenic Parasites
disease-causing parasites
Pathogenic parasites
Different Kinds of Hosts:
- Definitive host
- Intermediate host
- Paratenic host
- Reservoir host
- Natural host
- Accidental host
a host that harbors a parasite in the adult stage or where the parasite undergoes a sexual method of reproduction.
Definitive host
harbors the larval stages of the parasite or an asexual cycle of development takes place. In some cases, larval development is completed in two different intermediate hosts, referred to as first and second intermediate hosts.
Intermediate 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 detectable morphological change of parasite. Also known as the Transport host.
Paratenic host
a host that makes the parasite available for the transmission to another host and is usually not affected by the infection.
Reservoir host
a host that is naturally infected with certain species of parasite.
Natural host
a host that is under normal circumstances not infected with the parasite.
Accidental host
Three common symbiotic relationships between two organisms:
- Mutualism
- Commensalism
- Parasitism
Effects of parasites on the host:
- Direct Defects
- Indirect Effects
Under Direct Defects:
- Mechanical injury
- Deleterious effect of toxic substances
- Deprivation of nutrients, fluids and metabolites
may be inflicted by a parasite by means of pressure as it grows larger
Mechanical injury
Example of mechanical injury:
Hydatid cyst causes blockage of ducts such as blood vessels producing infraction
Ex: It is where a Plasmodium falciparum production of toxic substances may cause rigors and other symptoms.
Deleterious effect of toxic substances-
this is where a parasite may produce disease by competing with the host for nutrients.
Deprivation of nutrients, fluids and metabolites
Under Indirect Effects:
- Immunological reaction
- Excessive proliferation of certain tissue
includes size, shape, color and position of different organelles in different parasites at various stages of their development.
Morphology
This is especially important in laboratory diagnosis which helps to identify the different stages of development.
Morphology
Distribution of parasites depends upon:
- Host specificity
- Food habits
the route followed by a parasite from the time of entry to the host to exit, including the extracorporeal (outside the host) life. It can either be simple, when only one host is involved, or complex, involving one or more intermediate hosts.
Life cycle of parasites
infection is the result of entry and development within the body of any injurious organism regardless of its size
Host parasite relationship
Once the infecting organism is introduced into the body of the host, it reacts in different ways and this could result in:
- Carrier state
- Disease state
- Parasite destruction
a perfect host parasite relationship where tissue destruction by a parasite is balanced with the host’s tissue repair. At this point the parasite and the host live harmoniously, i.e. they are at equilibrium.
Carrier state
this is due to an imperfect host parasite relationship where the parasite dominates the upper hand. It can result either from lower resistance of the host or a higher pathogenicity of the parasite.
Disease state
occurs when the host takes the upper hand.
Parasite destruction
depending on the nature of the parasitic infections, the following specimens are selected for laboratory diagnosis:
a. Blood
b. Stool
c. Urine
d. Sputum
e. Biopsy material
f. Urethral, vaginal discharge, penile discharge
Laboratory diagnosis:
in those parasitic infections where the parasite itself in any stage of its development circulates in the blood stream
Blood
important part in the diagnosis of intestinal parasitic infections and also for those helminthic parasites that localize in the biliary tract and discharge their eggs into the intestine.
Stool
when the parasite localizes in the urinary tract, examination of this will be of help in establishing the parasitological diagnosis
Urine
Examination of this is useful in the following:
- In cases where the habitat of the parasite is in the respiratory tract, as in Paragonimiasis, the eggs of Paragonimus westermani are found.
- In amoebic abscess of lung or in the case of amoebic liver abscess bursting into the lungs, the trophozoites of E. histolytica are detected in the sputum.
Sputum
Examples of Biopsy material:
Spleen punctures in kala-aznar and muscle biopsy of Cysticercosis
Example for diagnosis of Urethral, vaginal discharge, and penile discharge
Trichomonas vaginalis
changes indicative of intestinal parasitic infections
Indirect evidences
changes indicative of intestinal parasitic infections
Indirect evidences
are carried out only in laboratories where special
antigens are available.
Serological tests
Indirect evidences where eosinophilia often gives an indication of tissue invasion by helminths, a reduction in white blood cell count is an indication of kala-azar, and anemia is a feature of hookworm infestation and malaria.
Cytological changes in the blood
