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Investigation of a Simple Model for Within-Flock Transmission of Scrapie.

Hagenaars TJ, Windig JJ - PLoS ONE (2015)

Bottom Line: In order to satisfactorily analyze the effectivity of control programs at the population level, insight is needed at the flock level, i.e., how the grouping of sheep in flocks affects the population-level transmission risk.We show that the data are consistent with a relatively simple transmission model assuming horizontal transmission and homogeneous mixing between animals.Here we provide an estimate of its mean value and variation for Dutch flocks.

View Article: PubMed Central - PubMed

Affiliation: Central Veterinary Institute, part of Wageningen UR, P.O. Box 65, 8200 AB Lelystad, The Netherlands.

ABSTRACT
Genetic control programs for scrapie in sheep build on solid knowledge of how susceptibility to scrapie is modulated by the prion protein genotype at the level of an individual sheep. In order to satisfactorily analyze the effectivity of control programs at the population level, insight is needed at the flock level, i.e., how the grouping of sheep in flocks affects the population-level transmission risk. In particular, one would like to understand how this risk is affected by between-flock differences in genotype frequency distribution. A first step is to model the scrapie transmission risk within a flock as a function of the flock genotype profile. Here we do so by estimating parameters for a model of within-flock transmission using genotyping data on Dutch flocks affected by scrapie. We show that the data are consistent with a relatively simple transmission model assuming horizontal transmission and homogeneous mixing between animals. The model expresses the basic reproduction number for within-flock scrapie as a weighted average of genotype-specific susceptibilities, multiplied by a single overall transmission parameter. The value of the overall transmission parameter may vary between flocks to account for random between-flock variation in non-genetic determinants such as management practice. Here we provide an estimate of its mean value and variation for Dutch flocks.

No MeSH data available.


Related in: MedlinePlus

FIS values histogram.Histogram of the FIS values calculated for 49 culled flocks with at least one secondary scrapie case. Negative FIS values, representing a heterozygote frequency excess, occur for 33 flocks.
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pone.0139436.g001: FIS values histogram.Histogram of the FIS values calculated for 49 culled flocks with at least one secondary scrapie case. Negative FIS values, representing a heterozygote frequency excess, occur for 33 flocks.

Mentions: In Fig 1 we show a histogram of the FIS values calculated for the genotype frequencies at the moment of culling for 49 flocks with at least one secondary scrapie case. Negative FIS values, representing a heterozygote frequency excess, occur for 33 flocks, indicating a recent history of selective breeding in these flocks.


Investigation of a Simple Model for Within-Flock Transmission of Scrapie.

Hagenaars TJ, Windig JJ - PLoS ONE (2015)

FIS values histogram.Histogram of the FIS values calculated for 49 culled flocks with at least one secondary scrapie case. Negative FIS values, representing a heterozygote frequency excess, occur for 33 flocks.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4591288&req=5

pone.0139436.g001: FIS values histogram.Histogram of the FIS values calculated for 49 culled flocks with at least one secondary scrapie case. Negative FIS values, representing a heterozygote frequency excess, occur for 33 flocks.
Mentions: In Fig 1 we show a histogram of the FIS values calculated for the genotype frequencies at the moment of culling for 49 flocks with at least one secondary scrapie case. Negative FIS values, representing a heterozygote frequency excess, occur for 33 flocks, indicating a recent history of selective breeding in these flocks.

Bottom Line: In order to satisfactorily analyze the effectivity of control programs at the population level, insight is needed at the flock level, i.e., how the grouping of sheep in flocks affects the population-level transmission risk.We show that the data are consistent with a relatively simple transmission model assuming horizontal transmission and homogeneous mixing between animals.Here we provide an estimate of its mean value and variation for Dutch flocks.

View Article: PubMed Central - PubMed

Affiliation: Central Veterinary Institute, part of Wageningen UR, P.O. Box 65, 8200 AB Lelystad, The Netherlands.

ABSTRACT
Genetic control programs for scrapie in sheep build on solid knowledge of how susceptibility to scrapie is modulated by the prion protein genotype at the level of an individual sheep. In order to satisfactorily analyze the effectivity of control programs at the population level, insight is needed at the flock level, i.e., how the grouping of sheep in flocks affects the population-level transmission risk. In particular, one would like to understand how this risk is affected by between-flock differences in genotype frequency distribution. A first step is to model the scrapie transmission risk within a flock as a function of the flock genotype profile. Here we do so by estimating parameters for a model of within-flock transmission using genotyping data on Dutch flocks affected by scrapie. We show that the data are consistent with a relatively simple transmission model assuming horizontal transmission and homogeneous mixing between animals. The model expresses the basic reproduction number for within-flock scrapie as a weighted average of genotype-specific susceptibilities, multiplied by a single overall transmission parameter. The value of the overall transmission parameter may vary between flocks to account for random between-flock variation in non-genetic determinants such as management practice. Here we provide an estimate of its mean value and variation for Dutch flocks.

No MeSH data available.


Related in: MedlinePlus