One-dimensional arrangement of flocks

Winter transmission only between neighbouring flocks

Summer transmission also between flocks which share grazing

Gene-flow between flocks

Selective breeding programmes

Force of infection: 0.0045 per farm per year

Mean outbreak duration: 5 years

No evidence for an increase in the force of infection before, during or after the BSE epidemic in British cattle

Estimate transmission parameters for scrapie in Cyprus

Investigate the impact of control measures

R ₀ = 1.4–1.8

Early identification and quarantine of affected flocks most effective for control of disease

Stochastic, spatial flock-level model

Acquisition of infection depends on trade

Probability and duration of a within-flock outbreak depends on flocks size and PrP genotype profile

Model is able to capture the spatial dynamics of scrapie

There is considerable uncertainty when predicting long-term trends for disease

Feasible to eradicate scrapie, but it will take decades to do so

The most-effective strategy is whole-flock culling, though whole-flock genotyping and selective culling is also effective

Simple age- and genotype-structured SI model

Flock structure ignored (same force of infection for all sheep)

Selective breeding strategies will reduce the prevalence and incidence

Targeting only the VRQ allele is sufficient to have a large impact on disease occurrence

R ₀ = 1.47 (95% CI: 1.45–1.50)

D = 2.11 years (95% CI: 2.01–2.23)

Large proportion of cases (80%) go undetected

Occurrence of scrapie may provoke changes in flock management which reduces outbreak duration

Within-flock R ₀ = 1.5–6.0

Formulate a flock-to-flock model of scrapie spread

Assess potential control programmes

SEI epidemic model with affected flocks of “low” and “high” risk (depending on genetic structure) which determines whether they experience outbreaks following exposure

Acquisition of infection depends on trade

R ₀ = 1.1–1.2

High risk flocks predicted to comprise 3–20% of the national population

Targeted programmes predicted to eradicate scrapie more quickly than those aimed at the general population

Develop a model for spread of scrapie in UK sheep population

Use the model to estimate infection prevalence (overall and by breed), and to evaluate possible long-term persistence of scrapie

Metapopulation model based on the coupling of fairly detailed within-flock SI epidemic models (genotype, age, and infection stage structure)

Flock-level acquisition of infection occurs by breeding, trading, or through homogeneous low-level contamination generated by all flocks

Flock-differ in breed, size, and PrP allelic composition

Detection/reporting probability of 16% (12–17)

Prevalence of infected animals in the population estimated to be 0.15%

9% of flocks estimated to be infected overall, rising to 60% in Shetland and 75% in Swaledale flocks

Assess impact of different strategies for control of scrapie in UK sheep

UK National Scrapie Plan (NSP) is the most effective scheme

NSP and UK Compulsory Scrapie Flock Scheme (CSFS) both reduce the case incidence, but CSFS is less effective in decreasing the susceptible allele frequency

Trading restrictions have a limited impact compared to selective breeding and culling