Influence on disease spread dynamics of herd characteristics in a structured livestock industry

Tom Lindström,Susanna Sternberg Lewerin,Uno Wennergren

doi:10.1098/rsif.2011.0625

Tom Lindström, Susanna Sternberg Lewerin + Show 1 more

Open Access

https://doi.org/10.1098/rsif.2011.0625

Copy DOI

Abstract

Studies of between-herd contacts may provide important insight to disease transmission dynamics. By comparing the result from models with different levels of detail in the description of animal movement, we studied how factors influence the final epidemic size as well as the dynamic behaviour of an outbreak. We investigated the effect of contact heterogeneity of pig herds in Sweden due to herd size, between-herd distance and production type. Our comparative study suggests that the production-type structure is the most influential factor. Hence, our results imply that production type is the most important factor to obtain valid data for and include when modelling and analysing this system. The study also revealed that all included factors reduce the final epidemic size and also have yet more diverse effects on initial rate of disease spread. This implies that a large set of factors ought to be included to assess relevant predictions when modelling disease spread between herds. Furthermore, our results show that a more detailed model changes predictions regarding the variability in the outbreak dynamics and conclude that this is an important factor to consider in risk assessment.

Highlights

With the aim of providing deeper understanding of the dynamics of livestock disease, researchers have recently focused much attention on the contact pattern between herds [1 – 10]
The final epidemic size is smaller for M2 than MMAM indicating that while there is initially on average a higher rate of infections of M2, the reversed is found in later stages of the outbreak
Kiss et al [23] conclude that heterogeneity in the number of contacts, which in M2 is introduced as an effect of herd size, may lead to a smaller final epidemic size

Summary

Introduction

With the aim of providing deeper understanding of the dynamics of livestock disease, researchers have recently focused much attention on the contact pattern between herds [1 – 10]. Such analysis may be used for predictions about disease transmission [11] as well as estimation of the effect of a changed contact pattern [12]. Different diseases spread with different vectors, but movements of animals between herds are generally considered to be a major risk factor for livestock disease transmission [13]. Assuming that a herd can only be infected once during a defined period of interest implies that reoccurring contacts between two herds will not generate additional disease transmissions. The effect of clustering may be illustrated by how it is usually quantified in network studies, i.e. clustering coefficient, which measures the frequency of ‘triplets’ in the contact network [18]

Objectives

Results

Conclusion