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The early drug selection of nematodes to anthelmintics: stochastic transmission and population in refuge

Published online by Cambridge University Press:  09 June 2006

S. GABA
Affiliation:
INRA, Research Unit Biometry, Domaine Saint-Paul – Site Agroparc 84914 Avignon Cedex 9, France INRA, Research Unit Animal Infectious Diseases and Public Health, 37380 Nouzilly, France
J. CABARET
Affiliation:
INRA, Research Unit Animal Infectious Diseases and Public Health, 37380 Nouzilly, France
V. GINOT
Affiliation:
INRA, Research Unit Biometry, Domaine Saint-Paul – Site Agroparc 84914 Avignon Cedex 9, France
A. SILVESTRE
Affiliation:
INRA, Research Unit Animal Infectious Diseases and Public Health, 37380 Nouzilly, France

Abstract

We have developed an individual-based model to reflect the complexity of the early phase of drug resistance selection in a nematode/sheep model. The infection process consists of the stochastic ingestion of infective larvae spatially aggregated in clumps. Each clump corresponds to infective larvae, which are the offspring of the mature nematodes from a given sheep. We studied the dynamics of the parasitic population and the frequency of the recessive resistance alleles during selection by anthelmintic treatments. The interaction between genetic and demographic processes illustrated the trade-off between the control of the infection and the delay of resistance selection. We confirmed the importance of the number of treatments and their timing. The same treatment frequency may result in different outcomes on resistance selection in relation to the size of the refuge (infective larvae on pasture). Treatment applied during the summer (when the mortality of infective larvae on pasture was high), may lead to a rapid selection of drug resistance and a lack of control of sheep and pasture contamination. We showed that higher stocking rates were also a force in promoting the resistance allele selection.

Type
Research Article
Copyright
2006 Cambridge University Press

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