Download Some useful Definitions

Some useful Definitions
Symbiosis
It was originally coined to refer to all cases where
dissimilar organisms or species (e.g. heterogenetic
associations) live together in an close association.
Major categories of Symbiosis
 Phoresis
 Commensalism
 Mutualism
 Parasitism
If we consider the degree of the association, then
phoresis and commensalism represent “loose”
associations, whereas mutualism and parasitism
indicate “intimate” associations.
Phoresis
(Phoresy)
Phoresis= migration;
it can mean “to carry.”
A type of symbiotic
relationship in which
one organism (the
smaller phoront) is
mechanically carried
on or in another species
(host).
‘The often overlooked
form of symbiosis!’
Phoresis
Phoresis
Carrion beetle with mites
Commensalism
Commensalism derives from the
English word commensal, meaning
"sharing of food" in human social
interaction, which in turn derives
from the Latin “cum mensa”,
meaning "sharing a table“.
Commensalism
occurs when one member of the
associating pair, usually the smaller,
receives all the benefit and the other
member neither benefits nor is
harmed.
Commensalism
• An orchid plant will attach itself high up a
tree trunk to have a safe, sheltered place to
grow and receive water dripping down the
tree trunk.
• The tree trunk which provides the habitat for
the orchid seems to neither be harmed nor
benefit from the relationship.
Mutualism
• Occurs when each member of the association
benefits the other.
• Mutuals are metabolically dependent on one
another
•This dependence can be facultative or
obligated, in the latter case one organism
cannot survive in the absence of the other.
Mutualism
Mutualism (facultative)
Mutualism (facultative)
The relationship between hermit crab and seaanemone is an excellent example of mutualism.
Hermit crab lives inside empty shell of mollusk.
The sea-anemone inhabits the outer surface of shell.
Sea-anemone is transported from place to place to get
food by crab. The Sea-anemone also gets food
captured by crab. The stinging cells of sea-anemone
protect the hermit crab from enemies.
Thus, both partners are benefited.
Mutualism (obligate)
Wolbachia and filarial nematodes
Wolbachia are common intracellular bacteria that are
found in arthropods and nematodes.
Outside of insects, Wolbachia infects a variety of
isopod species, spiders, mites, and many species of
filarial nematodes (a type of parasitic worm),
including those causing onchocerciasis ("River
Blindness") and elephantiasis in humans as well as
heartworms in dogs.
Mutualism (obligate)
Wolbachia and filarial nematodes
elephantiasis
onchocerciasis
("River Blindness")
heartworms in dogs
Mutualism (obligate)
Wolbachia within filarial nematodes are largely
mutualistic, with Wolbachia being essential for host
survival.
Wolbachia (stained red)
distributed throughout the lateral
hypodermal cord cells and
embryos within the uterus of
nematode (Onchocerca volvulus).
Cross section of adult female nematode
(Brugia malayi) stained with antibody
to Wolbachia surface protein (WSP).
Wolbachia (red) are present in the lateral
cords (LC) and ovaries (O)
Mutualism (obligate)
Applications to human health
Not only are these disease-causing filarial worms
infected with Wolbachia, but Wolbachia seem to play
an inordinate role in these diseases. A large part of
the pathogenicity of filarial nematodes is due to host
immune response toward their Wolbachia.
Elimination of Wolbachia from filarial nematodes
generally results in either death or sterility of the
nematode. Consequently, current strategies for
control of filarial nematode diseases include
elimination of Wolbachia via the simple doxycycline
antibiotic rather than far more toxic anti-nematode
medications.
Parasitism
Parasitos (para: beside; sitos: grain or food)
A symbiotic relationship in which one
organism (the parasite) benefits and the other
(the host) is generally harmed.
Parasites derive nutrition from their host and
may also gain other benefits such as shelter
and a habitat in which to grow and reproduce.
Overlapping
Now let’s focus on Parasitology
Some useful definitions in
Parasitology
Parasitism
Definitions of parasitism have traditionally focused
upon some ecological aspect of the parasite-host
interaction.
Here, I will pinpoint the aspect concerning the
metabolic dependency in the parasitological
relationships.
Metabolic Dependency
•
Parasites can be considered organisms which find
their nourishment and habitat on other living
organisms (belonging to a different species) without
destroying it (the host).
•
Parasitism is an intimate relationship between two
organisms during which time one organism (the
parasite) is metabolically dependent on the host:

Developmental Stimuli

Nutritional Dependence

Digestive Enzymes

Control of Maturation
Ecological relationship
Some researchers have stressed that parasites are
distinguished from free living organisms by their
habitat preference.
The habitat (=environment) is formed by another
living animal to which the parasite transferred “the
burden of regulating its relationship with the external
environment”!
Pathogenic Effects
Some parasitologists emphasized that parasites
produced harmful effects on their hosts
Parasitism is defined as the form of symbiosis in
which “one species lived at the expense of the other”
in the association.
I prefer another definition….
Webster’s Dictionary
“An organism living ‘in’ or ‘on’ another
living organism, obtaining from it part or
all of its organic nutriment, commonly
exhibiting some degree of adaptive
structural modification, and causing
some degree of real damage to its host”
An unambiguous definition?
•A number of parasitologists have concluded that
there is no distinct ecology, function, evolution,
or physiology that distinguishes all parasites
from all non-parasites.
•In essence, there is no such thing as an
unambiguous definition of parasitism because
only common ancestry is unambiguous in
biology, and parasites do not represent a
monophyletic group.
An unambiguous definition?
Parasitism is not a definition
but a condition!!!
Medical Parasitology
Parasitic diseases
Parasites
Prevention
Transmission
Treatment
Diagnosis
Pathogenesis
Life Cycle
Morphology
Conceptions related to medical
parasitology
 Symbiosis
 Parasite (stages and mechanisms of interaction
with the host and the environment)
 Life cycle
 Host (vector, reservoir, intermediate host,
definitive host)
Type of parasites
Protozoa
Nematodes
Parasites Helminths Trematodes
Cestodes
Arthropods Ecto-parasites
Endo-parasites
Endoparasite and ectoparasite
A parasite which lives in or on the body of the
host is called endo-parasite (protozoa and
helminthes) or ecto-parasite (arthropods).
Host and type of host
The host is an organism that harbors the parasite
(usually larger than the parasite).
 Intermediate host: The host harboring the larvae or
asexual stage of parasite.
 Final (definitive) host: The host harboring adult or
sexual stage of parasite.
 Reservoir host: Animals harboring the same species
of parasites as man (potential sources of human
infection).
Life cycle and type of life cycle
Life cycle: The whole process of parasite growing
and developing.
 Direct life-cycle: Only one host (no intermediate
host).
 Indirect life cycle: Life cycle with more than one
host (intermediate host and final host).
Relationship (Effect) between
parasite and host
Parasites injures to host
Host (animal or human) harbours parasite
the host’s immune response produces:
• Effects of the parasite on the host
• Effects of the host on the parasite
Effects of parasites on the host
• Depriving the host of essential substance
Hookworm Suck blood Anemia
• Mechanical effects of parasites on the host
Ascaris
Perforation/Obstruction
• Toxic and allergy effect (Hypersensitivity)
e.g. Proteolytic enzyme/Necrosis
e.g. Parasite antigen (anaphylaxix)
Effects of the host on the parasites
 The host can produce certain degree resistance to
parasites infection.
 The resistance (Immunity) is not very strong.
 In general, It doesn’t wipe out parasites completely,
but may limit the number of parasites and establish
balance with parasites.
• Innate immunity
• Acquired immunity (cellular and humoral:
antibodies)
Innate immunity
Barrier: Prevent parasites to invade in
certain degree.
Skin/Mucous Membranes/Placenta.
Acidity in skin or stomach can cause
damage of the parasites.
Phagocytosis: Non-specific/effective
against a wide range of parasitic infection
Acquired immunity
Mechanism: Cellular and humoral immunity.
Sterilizing immunity: Wipe out the parasites
completely, meanwhile get a long-term
specific resistance to re-infection. Rare!
Non-sterilizing immunity: Wipe out most of
the parasites, but not completely. Common!
The basic factor of transmission of
parasitic diseases
Parasitic diseases
Infectious diseases
Transmission
• The source of the infection
• The routes of transmission
• The susceptible host
The combined effect of those factors determines
the prevalence of the parasites at a given time
and place and regulate the incidence of the
parasitic diseases in certain local population.
The source of the infection
Patient: Persons who have parasites in
their body and show clinical symptoms.
Carrier: Persons who have parasites in their
body and do not show symptoms.
Reservoir host: Animals that harbor the
same species of parasites as man.
Sometimes, the parasites in animals can
transmit into human.
The routes of transmission I
Congenital transmission:
From mother to infant (Toxoplasmosis)
Contact transmission:
Direct contact (Trichomonas vaginalis)
Indirect contact (Ascaris lumbricodes)
Food transmission:
Food contaminated with the infectious stage of
parasites/The meat of the intermediate hosts
containing infectious stage of parasites.
The routes of transmission II
Water transmission:
Drink or contact the water contaminated the
infectious stage of parasites.
Soil transmission:
Contamination of the soil by feces containing
the certain stage of parasites and this stage can
develop into host.
Arthropod transmission:
Vectors of certain parasitic diseases.
The paths of invasion
Digestive tract:
Most common path of entrance (Food/Water
transmission)
Skin:
Infective larvae perforate skin and reach to body and
establish infection (soil/water transmission)
Blood:
Bloodsucking insects containing infective parasites
bite the skin and inject parasites into human blood
(arthropod transmission, i.e. malaria).
The prevention measures of the
parasitic diseases
Controlling the source of the infection.
 Treatment of the patients, carriers and reservoir hosts.
Intervention at the routes of transmission.
 Managing feces and water resource
 Controlling or eliminating vectors and intermediate hosts
Protecting the susceptible hosts.
 Paying attention to personal hygiene, changing bad eating
habit, taking medicine.