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High infection rates at low transmission potentials
One of the least understood processes in the transmission cycle
of filarial infections is the relationship between
the annual transmission potential
(ATP: no. of L3 transmitted to a human host per year)
and the parasite establishment rate
(PER: no. of adult parasites which establish in a host per year).
Whereas the ATP usually ranges from dozens
up to several thousands of L3 per host per year,
the PER usually amounts to a few parasites per host per year,
in onchocerciasis hardly exceeding values over five per year,
even at high ATPs.
We have investigated the relationship between
the ATP and the PER for 14 West African villages.
The PER increases rapidly with the ATP anda value of
0.3 parasites per year can already be possible
for ATPs of only ~10 L3 per man and year
(the value of 0.3 parasites per year seems low, but
it is an average over the whole population, with many
children who have low parasite burdens).
The PER is not necessarily proportional to the ATP,
and villages even exist where higher ATPs
are associated with lower PERs
(e.g. Guinea villages Gu863, Gu867, Gu910).
This shows that the establishment rate underlies
considerable variability and that it may substantially
be influenced by factors other than the ATP.
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Figure: Relationship between the parasite establishment rate (PER) and the annual transmission potential (ATP).
(A) Linear least-squares fit through zero on a log-transformed scale.
(B) Same data and same fit as in A, but shown on a linear scale to illustrate the degree of limitation.
(Source: Duerr HP et al., 2006)
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Comparing the estimates of all 14 villages suggests considerable limitation in the relationship between the ATP and the PER implying that
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the maximum PER is already reached for ATPs of some hundred L3 per person and year. The consequence for successfully controlled regions is that already a slight increase in the ATP may lead to a considerable increase in the PER.
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the average PER remains almost constant at higher ATPs, even if these differ by magnitudes. The consequence for the control of onchocerciasis is that lowering the ATP from very high to moderate values (say from 2000 to 500 L3 per person and year) may result in only a minor reduction in the infection of humans.
Related pages:
Limitation & control,
Eradicability,
Infection & immunosuppression.
Further reading:
Duerr HP, Leary CC, Eichner M, 2006.
High infection rates at low transmission potentials in West African onchocerciasis.
International Journal for Parasitology 36: 1367-1372.
Abstract in PubMed
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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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Collaborateur:
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Prof. K. Dietz, Institut für Medizinische Biometrie (IMB), Tübingen
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Prof. M. Eichner
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Prof. Dr. H. Schulz-Key |
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Soutenu financièrement par:
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Deutsche Forschungsgemeinschaft (DFG, DI 308/12-1)
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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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