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Open Access Research article

Potential for epidemic take-off from the primary outbreak farm via livestock movements

Michael J Tildesley13*, Victoriya V Volkova24* and Mark EJ Woolhouse2

Author affiliations

1 Centre for Immunity, Infection and Evolution, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, Kings Buildings, West Mains Road, Edinburgh, EH9 3JT, UK

2 Epidemiology Group, Centre for Infectious Diseases, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, Kings Buildings, West Mains Road, Edinburgh, EH9 3JT, UK

3 Centre for Complexity Science, Zeeman Building, University of Warwick, Coventry, CV4 7AL, UK (Current address

4 Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, S2-064 Schurman Hall, Ithaca, New York 14853, USA (Current address

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Citation and License

BMC Veterinary Research 2011, 7:76  doi:10.1186/1746-6148-7-76

Published: 24 November 2011

Abstract

Background

We consider the potential for infection to spread in a farm population from the primary outbreak farm via livestock movements prior to disease detection. We analyse how this depends on the time of the year infection occurs, the species transmitting, the length of infectious period on the primary outbreak farm, location of the primary outbreak, and whether a livestock market becomes involved. We consider short infectious periods of 1 week, 2 weeks and 4 weeks, characteristic of acute contagious livestock diseases. The analysis is based on farms in Scotland from 1 January 2003 to 31 July 2007.

Results

The proportion of primary outbreaks from which an acute contagious disease would spread via movement of livestock is generally low, but exhibits distinct annual cyclicity with peaks in May and August. The distance that livestock are moved varies similarly: at the time of the year when the potential for spread via movements is highest, the geographical spread via movements is largest. The seasonal patterns for cattle differ from those for sheep whilst there is no obvious seasonality for pigs. When spread via movements does occur, there is a high risk of infection reaching a livestock market; infection of markets can amplify disease spread. The proportion of primary outbreaks that would spread infection via livestock movements varies significantly between geographical regions.

Conclusions

In this paper we introduce a set-up for analysis of movement data that allows for a generalized assessment of the risk associated with infection spreading from a primary outbreak farm via livestock movements, applying this to Scotland, we assess how this risk depends upon the time of the year, species transmitting, location of the farm and other factors.

Keywords:
livestock movement; seasonality; cyclicity; spread of infection; primary outbreak