Breeding programmes for TSE resistance in British sheep

Gubbins, Simon; Roden, J.A.

doi:10.1016/j.prevetmed.2005.08.001

Cited by 20 publications

(15 citation statements)

References 29 publications

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“…(a)No long-term persistence was observed for ε 3 <0.01.(b)The values β 1 = 2.80 and β 1 = 4.93 were the lower and upper bound estimates of Gubbins and Roden [6].For a full description of the parameters and of other parameter values used see table 1.…”

Section: Resultsmentioning

confidence: 99%

“…The change of N and X with respect to age and time is described by: where m i ( a ) is the non-scrapie mortality rate for genotype i (SL/SL, SL/RH or RH/RH) at age a , and h i ( a ) is the hazard function for the log-normal age-at-onset of scrapie distribution with genotype specific parameters μ i and σ i [6], representing death due to scrapie.…”

Section: Methodsmentioning

confidence: 99%

“…The number of infected newborns of genotype i is calculated following the approach of Gubbins and Roden [6], relating the proportion of newly infecteds to the current population prevalence and assuming that all animals of a given genotype experience the same force of infection, yieldingwhere β i is a genotype specific transmission parameter. The number of newborns of genotype i at time t is given bywhere ν i ( t ) denotes the proportion of genotype i animals in the newly born population of size N (0, t ) at time t .…”

Section: Methodsmentioning

confidence: 99%

“…[5], [6]). Although the numerous mathematical models and policies vary widely in their approach and underlying assumptions, they unanimously build upon the assumption that polymorphisms of the PrP gene are associated only with scrapie susceptibility and not with any other trait such as fitness or performance.…”

Section: Introductionmentioning

confidence: 99%

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Implications of Conflicting Associations of the Prion Protein (PrP) Gene with Scrapie Susceptibility and Fitness on the Persistence of Scrapie

et al. 2009

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BackgroundExisting mathematical models for scrapie dynamics in sheep populations assume that the PrP gene is only associated with scrapie susceptibility and with no other fitness related traits. This assumption contrasts recent findings of PrP gene associations with post-natal lamb survival in scrapie free Scottish Blackface populations. Lambs with scrapie resistant genotypes were found to have significantly lower survival rates than those with susceptible genotypes. The present study aimed to investigate how these conflicting PrP gene associations may affect the dynamic patterns of PrP haplotype frequencies and disease prevalence.Methodology/Principal FindingsA deterministic mathematical model was developed to explore how the associations between PrP genotype and both scrapie susceptibility and postnatal lamb mortality affect the prevalence of scrapie and the associated change in PrP gene frequencies in a closed flock of sheep. The model incorporates empirical evidence on epidemiological and biological characteristics of scrapie and on mortality rates induced by causes other than scrapie. The model results indicate that unfavorable associations of the scrapie resistant PrP haplotypes with post-natal lamb mortality, if sufficiently strong, can increase scrapie prevalence during an epidemic, and result in scrapie persisting in the population. The range of model parameters, for which such effects were observed, is realistic but relatively narrow.Conclusions/SignificanceThe results of the present model suggest that for most parameter combinations an unfavourable association between PrP genotype and post-natal lamb mortality does not greatly alter the dynamics of scrapie and, hence, would not have an adverse impact on a breeding programme. There were, however, a range of scenarios, narrow, but realistic, in which such an unfavourable association resulted in an increased prevalence and in the persistence of infection. Consequently, associations between PrP genotypes and fitness traits should be taken into account when designing future models and breeding programmes.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Implications of Conflicting Associations of the Prion Protein (PrP) Gene with Scrapie Susceptibility and Fitness on the Persistence of Scrapie

et al. 2009

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“…However, scrapie has a strong host genetic component at the ovine prion protein (PrP) gene, which influences both the risk of infection and the incubation period (Detwiler & Baylis 2003;Baylis et al 2004;Gubbins & Roden 2006;Tongue et al 2006). Five alleles of the PrP gene (defined by the amino acids at codons 136, 154 and 171) are commonly found in British sheep, which, in the order of increasing risk of clinical disease and decreasing age at onset, are: ARR; AHQ; ARH; ARQ; and VRQ.…”

Section: Introductionmentioning

confidence: 99%

Prevalence of sheep infected with classical scrapie in Great Britain: integrating multiple sources of surveillance data for 2002

Gubbins

2008

J. R. Soc. Interface.

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Estimates for the prevalence of sheep infected with classical scrapie are essential for assessing the efficacy of control strategies that have been implemented in Great Britain (GB). Here a back-calculation approach was used to estimate the prevalence in the GB national flock by integrating data on reported cases and the results of abattoir and fallen stock surveys for 2002. Prevalence estimates ranged from 0.33 to 2.06%, depending on the estimates used for the frequencies of prion protein (PrP) genotypes in the national flock and the stage of incubation at which the diagnostic tests used are able to detect infected animals. The risk of infection was found to be higher than that of clinical disease, especially in those PrP genotypes that have a later age at onset of clinical disease. Moreover, results suggest that a high proportion (more than 55%) of infected animals surviving to disease onset die on farm before clinical signs become apparent, which helps account for the high observed prevalence in the fallen stock compared with the abattoir survey. The analyses indicated that attention needs to be given to identifying the stage of incubation at which diagnostic tests are able to detect infected animals and obtaining better demographic data for the GB national flock.

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