Causes of delayed outbreak responses and their impacts on epidemic spread

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.