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Monitoring the effect of scrapie control policies that use genetics in different countries

Scrapie, the ovine prion disease, is the most common natural form of the transmissible spongiform encephalopathies (TSE), which also include Creutzfeld-Jakob disease in humans and bovine spongiform encephalopathy (BSE) in cattle. Whereas BSE infection has not been proven to exist in ovine animals under natural conditions, there is some uncertaintly about whether BSE may have infected the ovine population and may still be present in that population. Thus TSE infection in ovine animals poses a theoretical public health risk.
In this project we want to determine the effect of introducing a PrP genotype programme to reduce TSE incidence on the evolution of genotype frequencies, incidence of clinical disease, prevalence of infection and on relevant production traits, including reproduction parameters as well as on other diseases and mortality rates. The results will be used to create mathematical and genetic models that can help to determine an optimal breeding strategy for scrapie control.
Flocks in which breeding strategies for reduction of scrapie susceptibility are being used in France, The Netherlands and Italy will be closely monitored. Data on disease incidence and genotype distribution will be collected. Samples will be taken from lymphoid tissues to investigate the prevalence of infection. Data on breeding sheep performance, health and fertility will be collected and analysed in relation to PrP genotype to estimate possible direct effects of the PrP genotypes or indirect effects due to genetic linkage. The results will be used to create statistical, genetic and mathematical models, at flock level, at breed level and at national population level.

The objectives of this project are:
1. To determine the effect of introducing a PrP genotype programme on evolution of genotype frequencies, incidence of clinical scrapie and prevalence of scrapie infection,
2. To determine the effect of introducing a PrP genotype programme on relevant production traits and prevalence of other diseases,
3. To investigate of how to optimise a PrP genotype program using mathematical and genetic models; and to relate epidemiological and genetic models in order to predict and measure the efficiency/effect of the use of resistant rams at flock and population levels.

Progress to Date
During the first reporting period, a significant part of the tasks were done, as illustrated by the percentage of person months devoted to each workpackage, which was respectively around 35% of the planned time for WP1, 25% for WP2, 15% for WP3. Epidemiology and monitoring of affected scrapie flocks was implemented, in an experimental flock naturally affected in Italy, but also in private farms in France and the Netherlands. This was difficult because of the new TSE policy begun since 2002 in these countries. The number of flocks is important: 30 in France, 7 in the Netherlands. The main features of these flocks showed large variations related to size of the flocks, production (milk, meat), scrapie history and incidence, and first year of use of ARR/ARR rams. Such differences give opportunities to implement relevant epidemiological studies (even if difficult) and to provide the people involved in workpackage 3 with suitable parameters for modelling.
For modelling tasks, first at the flock level, essential preparatory work was performed regarding the formulation of candidate mathematical models for estimating the reproduction ratio R0 (measure for the spread of the infection within a flock) and the possible statistical techniques for this estimation. Norwegian data was collected to characterize the scrapie type Nor98 (majority of Norvegian cases since 1998). But, due to violation of assumptions with scrapie type Nor98 in the simulation model built, it was decided to continue the modelling work at national level using "classical" scrapie (VRQ-scrapie).

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Scientist responsible for the project

Woodham Lane, New Haw
KT15 3NB Addlestone
United Kingdom (The) - GB

Phone: +44 1932 357894
Fax: +44 1932 357230


Project ID QLRT-2000-01733
Area 5.1.1
Start date 01 January 2003
Duration (months) 48
Total cost 3 163 183 €
Total EC contribution   1 107 113 €
Status Ongoing

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