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The process of infection with filariae
From a modeling view, filaria infections are
characterized by three properties:
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Property 1: It is a chronic infection
in which some parasites per year
manage to establish in the human host.
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Property 2: The infection rate is low
compared to the transmission potential.
Thus, the host resistance efficiently
controls the majority of the infection,
but it is not fully protective.
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Property 3: At higher transmission potentials,
the infection rate does not increase further,
it seems to be limited.
All three properties can easily be demonstrated in villages where
the average parasite burden does not profoundly differ despite an
annual transmission potential (ATP) which differs by magnitudes
(see Infection rate).
The parasite burden which develops only slowly over age, however,
raises the question: Why is the human host somehow better protected
against infection during the first years of life?
We try to explain this by the following model:
The human host is effectively, but not fully,
protected against infection with the parasite
(arrows 1 and 2 in the figure below).
If an infectious larvae (L3) manages to establish
successfully in a host, then, immunosuppressive processes
are initiated by adult worms and/or by microfilaria,
facilitating future infections.
As the parasite acquisition rate increases
slowly along with the developing parasite burden in a host,
his or her parasite burden increases only slowly over age,
explaining the patterns found in the
age-intensity profiles .
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Figure: Model of parasite acquisition in filarial infections, which occur density-dependently due to parasite-induced immunosuppression.
ATP Annual Transmission Potential of infectious larvae (L3).
L4: Intermediate larval stage. W: Adult, female parasite.
Mf: Microfilariae.
I: Protective immunity against L3.
Arrow 1: Immune-stimulation by a developing L3/L4.
Inhibition 2: Protective immunity can suppress the development of L3.
Inhibition 3: Adult parasites and/or microfilariae suppress immunity.
(Source: Duerr et al., 2003)
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Related pages:
Parasite acquisition,
High infection rates at low transmission potentials.
Further reading:
Duerr HP, Dietz K, Schulz-Key H, et al., 2003.
Density-dependent parasite establishment suggests infection-associated immunosuppression as an important mechanism for parasite density regulation in onchocerciasis.
Transactions of the Royal Society of Tropical Medicine and Hygiene 97: 242-250.
Abstract at PubMed
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Responsible for this page:
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Dr. H.-P. Duerr
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Webmaster:
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Prof. Dr. M. Eichner
(last change of this page on
13 July 2009)
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Cooperation with:
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Prof. K. Dietz, Institut für Medizinische Biometrie (IMB), Tübingen
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Dr. M. Eichner
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Further project partners:
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Prof. H. Schulz-Key, Institute for Tropical Medicine, University of Tübingen, Germany
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Financial support by:
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Deutsche Forschungsgemeinschaft (DFG, DI 308/12-1) |
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Disclaimer:
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Eberhard-Karls-University Tübingen,
Tübingen University Hospital,
the Department for Medical Biometry (IMB),
and the authors of this page disclaim all liability for the content of any page referenced by hyper-link from this page
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