DOI: 10.25349/d9p315
title: Causes of delayed outbreak responses and their impacts on epidemic spread

description: Livestock diseases have devastating consequences economically, socially,
 and politically across the globe. In certain systems, pathogens remain
 viable after host death, which enables residual transmissions from
 infected carcasses. Rapid culling and carcass disposal are
 well-established strategies for stamping out an outbreak and limiting its
 impact, however, wait-times for these procedures, i.e., response delays,
 are typically farm-specific and time-varying due to logistical
 constraints. Failing to incorporate variable response delays in
 epidemiological models may understate outbreak projections and mislead
 management decisions. We revisited the 2001 foot-and-mouth epidemic in the
 United Kingdom and sought to understand how misrepresented response delays
 can influence model predictions. Survival analysis identified farm size
 and control demand as key factors that impeded timely culling and disposal
 activities on individual farms. Using these factors in the context of
 existing policy to predict local variation in response times significantly
 affected predictions at the national scale. Models that assumed fixed,
 timely responses grossly underestimated epidemic severity and its
 long-term consequences. As a result, this study demonstrates how general
 inclusion of response dynamics and recognition of partial controllability
 of interventions can help inform management priorities during epidemics of
 livestock diseases.
description: We integrated different types of response delays into the
 well-established Warwick model. The model includes spatially explicit
 representation of registered farms and their livestock compositions. It
 treats the farm as the basic unit for infection and susceptibility, such
 that all the animals in each holding become infected en masse. The
 parameters are fitted to the incidence data from 2001 and account for
 nonlinear increases of farm-level transmission and susceptibility as a
 function of farm size. The original model description of control actions
 is extended to include the disposal process, carcass transmission rate,
 and variable culling and disposal delays that equate to an individual
 farm’s wait-times in the control queues. The model simulates a general
 scenario where only infected premises and premises with known dangerous
 contacts are targeted for removal. Additional details of the Warwick model
 can be found in: Keeling et al. (2001) Dynamics of the
 2001 UK foot and mouth epidemic: stochastic dispersal in a heterogeneous
 landscape. Science, 294, 813–817.<br> Keeling et al. (2003)
 Modelling vaccination strategies against foot-and-mouth disease. Nature,
 421, 136–142.<br> Tildesley et al. (2008) Accuracy of models for the
 2001 foot-and-mouth epidemic. Proc. Biol. Sci., 275, 1459–1468.<br>
 Tildesley et al. (2017) Mathematical Models of the Epidemiology and
 Control of Foot-and-mouth Disease. Foot and Mouth Disease Virus: Current
 Research and Emerging Trends.<br> Probert et al. (2018) Real-time
 decision-making during emergency disease outbreaks. PLoS Comput. Biol.,
 14, e1006202.