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Limitation
Limitation is based on negative feedback
which is very common in nature.
A well-known representation is crowding:
Mortality within a population increases
when its density approaches the capacity of the habitat.
Limitation is a basic principle in a finite world.
The corresponding type of curve shows a saturation profile:
the slope of the curve decreases with increasing 'x',
and approaches a limiting value for high values of 'x'.
Limitation in the transmission of filaria occurs, for example,
if flies die from an "overdose" of ingested microfilaria.
Figure: Fitting a limited and a non-regulated relationship
to the same data leads to an intersection between both curves.
This intersection is a stable equilibrium representing
the endemic state.
The trivial equilibrium (the infection-free state) is
in this case instable. Without external influences,
the system tends towards the endemic state (gray arrow).
Limitation processes 'limit' the eradicability of an infection,
because they stabilize the endemic state and
destabilize the infection-free state.
Limitation is a very efficient process for pathogens
to maximize their persistence in the host population:
the pathogen quickly (at small values of 'x') establishes in the host,
and the asymptotic behaviour guarantees for stable transmission
over a wide range of transmission intensities,
without damaging or klling the habitat, the host population.
The opposite of limitation is
facilitation
- a process with positive feedback which 'facilitates'
the eradicability of an infection.
Further reading:
Duerr HP, Dietz K, Eichner M, 2005.
Determinants of the eradicability of filarial infections: a conceptual approach.
Trends in Parasitology 21: 88-96.
Abstract at PubMed
Related pages:
Facilitation,
Limitation & Control,
Eradicability of onchocerciasis,
Uncertainties in the eradicability.
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Responsable de cette page:
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Dr. H.-P. Duerr
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Webmaster:
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Prof. Dr. M. Eichner
(dernière modification de cette page:
13 juli 2009)
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Traduit en français par:
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Claire Le Roux,
Université de Valenciennes et du Hainaut Cambraisis (UVHC),
Institut des Sciences et Techniques (ISTV), France
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Avertissement:
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L'Université Eberhard Karl de Tübingen,
le Centre Hospitalier Universitaire de Tübingen,
le Département de Biométrie Médicale (IMB),
ainsi que les auteurs de cette page déclinent toute responsabilité pour le contenu des pages auxquelles cette page renvoie
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