Centre of Excellence in Epidemiology, Population Health
& Infectious Disease Control (EPIC)
University of Edinburgh
Executive Summary of Risk Assessment
of introduction and maintenance on Scottish Agricultural holdings
of Foot and Mouth Disease (FMD) virus
responsible for the FMD outbreak in England
declared on 3 August 2007
23 August 2007
Dr Nick Savill, Dr Victoriya Volkova, Paul Bessell
Researchers at the University of Edinburgh were asked by the Scottish Executive to assess the risk of opening livestock markets in Scotland. The risk is that there is undetected Foot and Mouth Disease infection on a livestock farm in Scotland and that opening the markets would spread infection across the country creating a national epidemic. Risk was assessed in two steps: contact tracing of animal movements from farms in Surrey into Scotland, and daily calculation of the chance that there is still undetected infection in Scotland.
Contact tracing used national animal movement databases that record individual cattle movements and batch movements for sheep, pigs and goats. Tracing identified only a handful of contact chains from Surrey to 12 premises in Scotland. Six sheep were moved on 21 July from a single holding within 20km of the confirmed FMD cases in Surrey to a Welsh showground. Five days later sheep were moved from this showground, either directly or indirectly through a market, onto 5 holdings in Scotland. Whether they were the same sheep is impossible to tell because of the nature of the database. Four contact chains were identified for cattle movements from Surrey into Scotland. They began on the 16 and 20 July and ended in 110 animals moving onto 6 holdings in Scotland on 1 August and 1 animal moving onto another holding on 2 August. None of these cattle came from Surrey. All 12 holdings have been checked by veterinarians with no signs of infection. Whilst carrying out their inspections the veterinarians identified 3 unrecorded movements to other holdings. These have been checked and no signs of infection were found.
If there is undetected FMD infection in Scotland now, an estimate of when it might be detected in the future can be made. As time passes, and if no detection happens, it becomes more and more likely there is no infection in Scotland. To err on the side of caution it is best to assume that all livestock holdings in Scotland could have been exposed to FMDV but only a single holding is infected. On advice from the Scottish Executive, detection of infected animals is assumed to occur when they are moved under licence to slaughter or for welfare reasons, when they are moved within the same business, or when their FMD incubation has passed and they begin to show symptoms. Rates of movements used in the analysis are based either on available records or on expert veterinary opinion. Because of uncertainty in incubation periods for this strain of FMD virus in different livestock species, different incubation periods are examined to get a range of possible detection dates. Analyses indicate that if FMD is not detected in Scotland by early to mid September then it is highly likely, although not guaranteed, that Scotland is free of FMD.
Risk maps were produced that show the potential impact of spread of infection across Scotland if the disease either spread locally or spread via movements through markets.
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