Vet Record June 29 2002
SIR - The present contingency plan to deal with any further incursions of FMD into the UK is still based on the principle of the 24 hour slaughter of infected premises and the slaughter of contiguous premises within 48 hours.
The policy was inrtroduced at the height of the 2001 epidemic and was adopted following the mathematical modelling of Professor Anderson's group at Imperial College, London. Subsequently, the accuracy of the model has been questioned due to its reliance on data that my have been inaccurate or which omitted vital management and husbandry information.
The model predicted that the outbreak should, under the contiguous cull policy, have been over in June 2001. However, it was not until the introduction of 'blue boxing' under veterinary control, first in the Thirsk outbreak and then the Penrith triangle, that outbreaks were swiftly resolved, with the final outbreak confirmed on September 30, 2001.
More disturbingly, the Chief Scientist, basing his reasoning on the same computer models, declared that there were to be no autumn movements of sheep within the UK unless they were tested and found to be serologically negative before movement. His decision was again based on the Imperial College group's computer model, which, he stated, indicated that any relaxation of movement would prolong the outbreak well into the spring of 2002. This was vigorously opposed by the Sheep Veterinary Society and, in conjunction with the National Sheep Association, the autumn movement regime was insitituted based on veterinary risk assessment. No outbreaks have occurred since September 30!
Compouter modelling can be an aid to decision making, just as an x-ray is an aid to diagnosis. To use unproven prediction models relying on potentially flawed data as a sole basis for future contingency planning is questionable and conveys a certainty which is unjustified. It must not be forgotten that over 200 owners successfully prevented the slaughter of their livestock under the contiguous cull and none of these flocks subsequently suffered overt disease. The sporadic cases which occurred early in the outbreak in Northamptonshire, Wiltshire and Oxfordshire were all successfully contained using tried and tested methods of slaughter of the infected premises and of dangerous contacts using veterinary risk assessment to determine the dangerous contacts.
The Sheep Veterinary Society believes that a policy based on computer modelling alone should be abandoned, especially when it is our understanding that the initial models used in March 2001 have yet to be published in full for independent peer review. Future planning must involve veterinary risk assessment and the contiguous cull polciy should be replaced by slaughter policy of true dangerous contacts only.
Furthermore, we would also urge policy makers in the transmissible spongiform encephalopathy field to be equally aware of the poetential limitations of computer modelling and for the need to always place increased reliance on verifiable scientific evidence wherever possible.
Ian Gill (President), Chris Lewis, Colin Macaldowie (Secretary), Sheep Veterinary Society, Pentlands Science Park, Bush Loan, Penicuik EH26 0PZ