FOOT AND MOUTH DISEASE
VETERINARY RISK ASSESSMENT (NO.16)
REMOVING THE RESTRICTED ZONE CONTROLS IN SCOTLAND
Background
When a further outbreak of FMD was confirmed in Surrey on 12 September an immediate GB wide national movement ban was introduced following the re-imposition of a Restricted Zone. In Scotland, certain exemptions from the movement ban were introduced simultaneously to allow urgent husbandry tasks such as milking to continue. Movements to alleviate urgent welfare problems and direct to slaughter were also permitted. Farms on the Scottish islands were not subject to the RZ controls.
Over the following weeks further relaxations of the movement ban have resulted in a number of normal farming activities being permitted including:
- movement of animals to slaughter via collection centres - 16 September
- movements within a farm business up to 8 km - 20 September
- movements between farms anywhere in the RZ but with a 20 day standstill period on the destination farm- 25 September
- slaughter sales - 28 September
- store and breeding sales - 2 October
There have also been other relaxations permitting the resumption itinerant livestock services and multiple pickups and drop-offs between premises.
In comparison with pre-August conditions the temporary safeguard measures remaining in force are the 20 day stand still in place of the usual 13 day standstill period and the cancellation of the system of authorised separation agreements.
Bringing FMD virus to Scotland - the main risk factors
There is a hierarchy of risk of spreading FMD from an infected premises by the movement of livestock, their products and other mechanical means. In decreasing order these are:
- livestock
- livestock vehicles, farm tractors and machinery
- other equipment used in connection with handling or other livestock related procedures, such as sheep shearing, dipping
- hay and straw
- livestock handlers' boots and clothing
- non-farming members of the public
Livestock
Livestock are the greatest risk because they actively excrete FMD virus. The incubation period for the present strain causing the Surrey outbreak is thought to be between 5-8 days. All susceptible livestock excrete FMD virus in breath, saliva, milk, urine and faeces for up to 4 days before the appearance of clinical signs. Observations on the infected farms in Surrey have shown that disease has not been recognised quickly by farmers and stockmen for five to 10 days after lesions first appear. Experience from 2001 has also shown that FMD in sheep is difficult to spot, leading to a higher risk of sheep spreading infection, so-called silent spread.
Moving livestock during an FMD outbreak increases the risk of spreading infection to premises which were previously uninfected. The risk is that undisclosed infection will be carried to new locations. The important risk factors are:-
- infection might have been brought to Scotland by direct or indirect movements of animals from infected farms
- undisclosed FMD at the premises of departure in Scotland or the premises from which the transport was despatched.
- spread by susceptible livestock incubating disease or with unrecognised lesions.
- silent spread of FMD by sheep
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Vehicles, tractors, machinery and other equipment
Vehicles, tractors, machinery and other equipment which have come from an infected farm can be heavily contaminated with FMD virus and can physically carry the infection elsewhere.
The onset of the disease in Surrey coincided with the main shooting seasons in Scotland. Many clients travel from the south east of England for the deer and game bird shooting. The vehicles used could potentially have come from infected farms in Surrey.
There are occasional movements of horses in both directions across the border between England and Scotland. These would generally be to a major equestrian event or race meeting.
Hay and straw
Survival of FMD virus will be highly variable under field conditions but can be up to 20 weeks on hay or straw.
Farmers and other livestock handlers. Farmers and other livestock handlers are a risk because of the likelihood that they will have had close contact with infected animals when visiting other farms. (Other non-agricultural visitors present a significantly lower risk).
Evidence that FMD is not present in Scotland
Livestock tracings
Since 15 July 2007 there have been very few direct or indirect contacts with premises close to the infected premises in Surrey. The CTS, AMLS and SAMS databases were interrogated during both phases of the current outbreak and these have shown:
Outbreak cluster 1
- no direct movements of sheep, goats or pigs from the county of Surrey to Scotland since the beginning of July up to the present.
- no direct movements of cattle, sheep, goats or pigs to Scotland from within 20 km of the first two infected farms and their associated dangerous contact farms from the beginning of July until 8 September when the first period of the outbreak was declared to be over.
- a contact tracing exercise conducted by EPIC revealed that there were 15* farms in Scotland which had indirect links to farms within 20 km of the first two infected farms and their associated dangerous contact farms from the beginning of July until 8 September.
Outbreak cluster 2
- three* direct movements of cattle to Scotland from within 50 km of the Pirbright Laboratory from 15 July up to the present
- no movements of sheep, goats or pigs from within 50 km of the Pirbright Laboratory from 15 July up to the present
- a contact tracing exercise ( see footnote) conducted by the University of Edinburgh partner in EPIC revealed that there were 19* additional farms in Scotland which had indirect links to farms within 50 km of the Pirbright Laboratory from 15 July up to the present
* Animal Health veterinary staff visited and inspected all the susceptible livestock on these farms with negative findings.
Livestock inspections
Large numbers of farm to farm movements have taken place since the initial restrictions imposed in August were relaxed and re-imposed in September. The earliest movements during both phases of the outbreak were only permitted subject to a preliminary veterinary inspection.
Thousands of animals have been slaughtered since the first week in August. All of these animals have been subjected to both ante and post mortem inspection without any signs of FMD being detected.
Collection centres (16 September), slaughter markets (1 October) and store and breeding sales (4 October) have all been operating under veterinary supervision of all susceptible livestock present.
Any of the permitted movements, whether under a specific or general licence, carried a risk of spreading disease and conversely of detecting undisclosed infection.
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Vehicles, tractors, machinery and other equipment
There is no established movement of agricultural machinery from the south of England to Scottish farms. Dipping, shearing and other contractors working in Scotland generally move relatively short distances and would not be expected to come from any further south than the north of England.
Vehicles transporting horses over long distances are generally well maintained and in a clean condition. The likelihood of physical transfer of infection on such vehicles is not high.
On many of the larger shooting estates, the clients would be transported around the hill on estate transport. On some of the lower ground game bird shoots, for example in the Borders, the clients may use their own four wheel drive vehicles. However, the main shooting season will not get under way until the leaves have fallen from the trees later in the autumn.
Hay and straw
Any straw used on Scottish farms tends to move across the country from east to west. Very little, if any, straw is sourced from areas south of the border. Hay, where fed, would be produced on farm or be expected to come from lowland areas in Scotland relatively close to hill farms where it might be fed. Transport costs preclude long distance haulage of hay and straw.
Farmers and other livestock handlers
Work done by the Defra epidemiology team has confirmed that there are no outstanding people or vehicle tracings from any of the eight Infected Premises. The only counties put at risk by ongoing personnel, equipment and vehicle tracings from IPs are Surrey (6), Hampshire (4), West Sussex (4). These had all received initial visits and are negative to date (3 October), but have been marked forward for final revisit 21 days post contact.
With the exception of potential buyers of breeding bulls and rams, there would not be many visits to Scottish farms by farmers in the south east of England.
Comment
At the time of writing there is still diminishing evidence of FMD virus circulating within the current Protection Zone. The risk that FMD virus has been brought to Scotland at the present time is very low but above the pre-outbreak level.
The residual risk
The Defra FMD 2007 Epidemiology Report dated 30 September 2007 states that the six IPs that have occurred in September are all contained within a small area about 16 km north of the Pirbright laboratory. The evidence available suggests that IP5 is likely to have been the first of this group to become infected either from the Pirbright site or from one of the original two IPs. IP8, the last case to be confirmed, is thought to have been infected from IP3. Animals on one of the several parcels of land which comprise IP8 will have remained infectious until 1 October.
The report also considers the possibility of FMD virus being outside the PZ/SZ. It quotes expert opinion that it is unlikely that virus from the original release from the Pirbright site is still infectious. Therefore if FMD exists outside the PZ/SZ it has been taken there either by infected livestock or mechanical transmission by vehicles or equipment.
An analysis of animal movement data by the epidemiology team has confirmed studies already carried out by the University of Edinburgh partner in the EPIC team that there were no direct movements of animals to Scotland from the PZ or SZ during the three months, July to September. Most of the movements that have taken place during July to September have involved relatively small numbers of animals (thousands rather than tens of thousands) and almost half of these moves have been within Surrey.
Although the full analysis of movements has not been completed, the report concludes that it is unlikely that any holdings outside the FMD risk area will be found to have been placed at risk. The numbers of report cases in the southern part of England which have been investigated to date (approximately 190) indicates a high level of awareness and shows that surveillance for FMD is being carried out.
It is still possible, though very unlikely, that an infected animal could be moved from a premises in Surrey and brought to Scotland illegally. A more realistic possibility is that viable FMD virus may still be present on premises in Surrey and could be brought by a vehicle to a farm in Scotland. FMD virus is capable of remaining viable for weeks in cool damp conditions where it is not exposed to heat such as under the wheel arches of vehicles. It is therefore possible that a vehicle which had driven on to infected land in Surrey could bring the virus directly to Scotland, as discussed above.
In summary, the residual risk to Scotland is from two possible sources: (1) illegal introduction of an infected animals and (2) mechanical transmission by vehicle. The residual risk is therefore very low but not yet down to inter-epidemic levels.
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The effect of introducing FMD to Scotland during the current period
The impact of that the introduction of FMD virus would have in Scotland would depend on the type of premises first infected, the time of the year and its location.
Farms
FMD can be spread easily between farms by
- nose to nose contact across boundaries
- aerosol spread can occur but only under certain favourable conditions
- moving animals to market or directly to other farms
- the movement of livestock vehicles
- stockmen travelling to outlying land to feed stock
- the movement of farm machinery from farm to farm
- visitors from other farms.
In the absence of any movements of animals, vehicles or people between farms experience, supported by modelling studies, has shown that the risk of spread from farm to farm is greatest in the south west of Scotland (Dumfries & Galloway and Ayrshire). In other parts of Scotland the spread of disease from farm to farm directly could still occur but probably not at the same rate. In crofting counties on the mainland, the widespread use of common grazing would tend to facilitate disease spread.
Movements from farms on the mainland are currently limited by a basic 20 day standstill rule, with certain exemptions for movements assessed to present a lower risk. These include movements to veterinary premises for treatment or research and the movement of male breeding animals.
FMD introduced to a farm in Scotland could spread rapidly to neighbouring farms and to others receiving livestock from that farm. Direct movements could, in theory, set up disease on farms in five other areas because multiple pickups and drop-offs (three of each) are now permitted.
Farms on the islands
Although the risk of FMD reaching island farms is lower, if the virus reached an island, farms on the island would be more vulnerable because of the less stringent animal movement regime.
Animal gatherings
Any gathering of animals which brings together animals from a large number of farms and then involves dispersal to a number of other farms could also result in the dissemination of virus resulting in a starburst of disease. Unrecognised or inapparent disease in animals attending gatherings on unpaved surfaces which are re-used too soon could result in a build up of contamination resulting in the carrying over of infection from one gathering to another. The widespread lack of understanding of the importance of basic hygiene among many in the livestock industry means that persons attending a gathering such as a show or sale are highly likely to take infection home even if no animals are brought on to their premises.
Collection centres for animals intended to travel directly to slaughter present a lower risk of spreading infection because the animals cease to be 'virus factories' immediately after death.
Conclusion
The likelihood that undetected FMD virus is currently present in Scotland is very low. Intensive tracing, sampling and surveillance work is being carried out in the PZ and SZ in Surrey to confirm that by the time the PZ controls fall the risk of viable FMD virus remaining is Surrey will have become very low indeed. The risk to the Scottish livestock industry of introducing the FMD virus currently circulating in Surrey remains above normal levels and mitigation measures continue to be appropriate. However, the lifting of the Protection Zone provides greater confidence that the FMD virus is no longer circulating. Taken with the time that the national movement ban will have been in place (some four incubation periods) it is concluded that the reduced levels of risk justify the removal of the remaining temporary safeguard measures at the time the Protection Zone is lifted.
Veterinary Division
Rural Directorate
Scottish Government
9 October 2007
Footnote
The movement databases were interrogated to perform contact tracings. Each animal movement database was scanned for any movements between the dates in question from holdings within the 20km and later 50km zone. Any movements into Scotland were recorded. The database was scanned a second time for any movements from the secondary holdings to tertiary holdings that occurred on the same day or after the primary to secondary movements. Again, any movements into Scotland were recorded. This process was repeated until no further movements were possible. To speed this process, all movements to abattoirs, which are of less epidemiological importance than other movements, were removed from the databases.
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