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Uncertainties in the control of filariasis
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The
eradicability
of a filarial infection can be affected
by density-dependent side effects of certain interventions.
The figure below shows how the
persistence graph
(lower graphs, colors see persistence graph)
is altered by administration of a microfilaricide.
The pale-colored curve in each graph represents the persistence pattern
without intervention. The full-colored curves represent
the persistence patterns resulting from a microfilaricide-based intervention,
whereby density-dependent characteristics of the microfilaricidal effect
are shown in the upper graphs. In the three scenarios, the microfilaricide
reduces the microfilariae (Mf) density by 95% at the population level but
can deviate from this in a density-dependent manner by 2%.
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Figure: (a) An effect which might result from ivermectin-facilitated immunity.
As a result of this mechanism, the reduction in the Mf density improves in
(a) from 95% to 97% during the course of therapy (from right to left in the upper graph).
The corresponding
persistence graph
shows that under this assumption,
the threshold biting rate (TBR,
see also Glossary)
increases from ~900 to ~18000 bites per person per year,
suggesting that elimination might be easily achieved.
Compared with the TBR of ~11000 in the case of no density dependence
[scenario (b), 95% reduction independent of the Mf density],
a mechanism such as ivermectin-facilitated immunity can considerably
increase the prospects of elimination. In scenario (c),
chosen with respect to symmetry to (a), the reduction in the Mf density
declines from 95% to 93% during the course of therapy
(from right to left in the upper graph), which shifts the TBR
to ~8000 bites per person per year. The examples show that a slight variation
in the density-dependent side effects of an intervention can considerably
alter the prospects of elimination. (Source: Duerr et al., 2005)
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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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Financial support by:
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Deutsche Forschungsgemeinschaft (DFG, DI 308/12-1)
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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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