Control of equine influenza: scenario testing using a realistic metapopulation model of spread

Abstract

We present a metapopulation model of the spread of equine influenza among thoroughbred horses parametrized with data from a 2003 outbreak in Newmarket, UK. The number of horses initially susceptible is derived from a threshold theorem and a published statistical model. Two simulated likelihood-based methods are used to find the within-and betweenyard transmissions using both exponential and empirical latent and infectious periods. We demonstrate that the 2003 outbreak was largely locally driven and use the parametrized model to address important questions of control. The chance of a large epidemic is shown to be largely dependent on the size of the index yard. The impact of poor responders to vaccination is estimated under different scenarios. A small proportion of poor responders strongly influences the efficiency of vaccine policies, which increases risk further when the vaccine and infecting strains differ following antigenic drift. Finally, the use of vaccinating in the face of an outbreak is evaluated at a global and individual management group level. The benefits for an individual horse trainer are found to be substantial, although this is influenced by the behaviour of other trainers.

Transmission of Equine Influenza Virus during an Outbreak Is Characterized by Frequent Mixed Infections and Loose Transmission Bottlenecks

“…If the latent and infectious periods are long, like in a naïve population [44], very rapidly almost all infections will involve mixed infections. If vaccination results in shorter latent and infectious periods [15], then fewer infections will be mixed (40% in the parameterization in Figure 5), consistent with our finding of 52% of horses with mixed infections. Epidemic size also depends on whether infectious periods for mixed infections are longer or shorter (i.e.…”

“…(B) Proportion of reinfections in the Newmarket vaccinated population using data from experiments with heterologous vaccination for the latent and infectious periods [15].…”

What can mathematical models bring to the control of equine influenza?

“…Mathematical models already demonstrated that vaccination (especially with vaccines containing up‐to‐date strains) can work at a within‐yard level (Table ). A meta‐population model incorporating spread from yard‐to‐yard informed by data from the 2003 outbreak of equine influenza in Newmarket, which involved spread of infection between multiple yards , confirmed the previously anecdotal belief that vaccination in the face of an outbreak can be an effective control measure . The model also suggested that ‘poor responders’ can have a significant impact on the effectiveness of vaccination policies, particularly if these are clustered within a few yards in which there is active noncompliance with mandatory vaccination policies.…”

Facing the threat of equine influenza

“…The biological reason for this difference was not clear. More recently, modelling techniques have been applied to test the effects of horses that are poor responders during a large outbreak, affecting multiple yards and also the use of vaccination in the face of an outbreak (Baguelin et al . 2010).…”