Open Access

Table IV.

Summary of the models for the possible consequences of BSE in sheep.

Author(s) Aims Modelling approach Conclusions
Ferguson et al. [20] Estimate the human health risk from possible BSE infection in the GB sheep flock
  • Deterministic age-structured SI model for within-flock spread

  • Deterministic SIRS model for spread between flocks

  • Deterministic model for transmission to human population

  • Public health risk from ovine BSE are likely to be greater than from cattle

  • Risk could be reduced through additional restrictions on sheep products entering the food chain

  • Upper bound for vCJD cases increases to 150 000 when worst-case ovine BSE scenario included in predictions

Fryer et al. [25] Assess the impact of different control strategies to protect public health from exposure to BSE in sheep
  • Age- and genotype-structured within-farm model used to estimate the exposure of humans to infectivity from BSE-infected sheep entering the food chain

  • Assumes constant number (4) of BSE-affected flocks in GB

  • If BSE were present in the GB national flock, the exposure to consumers from a single infected sheep would be high

  • Annual exposure from four BSE-affected flocks could be considerable

  • Small reductions in exposure can be achieved by strategies based on tissue testing, a 12-month age restriction or expanded definitions of high-risk tissues

  • A 6-month age restriction is more effective

  • Genotype-based restrictions are most effective

Kao et al. [51] Estimate the possible size of a BSE epidemic in British sheep
  • Age- and genotype-structured model to predict size of feed-borne epidemic

  • Flock-level model to predict impact of horizontal transmission on epidemic

  • See also [51] (Tab. II)

  • Feed-borne epidemic peaked in 1990 with between 10 and 1 500 infected sheep

  • In 2001, at most 20 clinical cases of BSE would be expected

  • If horizontal transmission occurs, it could cause a large epidemic

Kao et al. [52] Assess the impact of ARR/ARR sheep being susceptible to BSE
  • Age- and genotype-structured model for feed-borne epidemic

  • Deterministic model for flock-to-flock transmission

  • See also [51, 54]

  • Predictions for size of feed-borne epidemic not affected if ARR/ARR animals can become infected

  • Selective breeding for ARR/ARR should control a BSE epidemic, but there are scenarios consistent with the data in which control fails