Bluetongue: Detailed rationale behind the policy statement
The current strategy is being delivered using disease control measures such as controlling the movements of susceptible animals, as set out in EU legislation. The rationale for this approach is set out below:
Vectors
- Bluetongue is spread between animals by a midge vector (Culicoides spp.). Infected midges have the potential to spread disease in a local area (up to 1.5-2km a day in some cases)
- It is neither possible nor proportionate to attempt to eradicate or control populations to an extent that would mitigate against or have a desired controlling effect on the spread of Bluetongue.
Susceptible animals
- Susceptible animals (i.e. all ruminants and camelids) potentially are a ‘reservoir’ for disease for up to 60 days when infected. Movements of infected animals has the potential to spread disease a much further distance than midges.
- It is extremely difficult/impractical to completely protect an infected animal from attack by midges. Therefore an infected animal provides a source of virus for a local midge population wherever it is located (and potentially further disease transmission in that local area)
- While it is not possible to stop the local spread of disease through movement of midges. It is possible to control the spread of disease through the control of movements of infected and potentially infected animals.
Disease control measures
Protection Zone
- A Protection zone is established in order to try to contain disease within an area around an infected premises. The Protection zone boundary should always be at least 20km away from any infected premises.
- Movements of animals and midges may still spread disease within the zone, however, sufficient surveillance and reporting of signs of disease should monitor the levels of spread, and new infected premises are most likely to be found within this zone.
- Even so, given the nature of the disease, it can be assumed that there will always be a level of undetected infection in the Protection Zone i.e. as clinical signs of disease are not always apparent.
- Therefore, any movement of susceptible animals out of the Protection zone has the potential to spread disease to a new and previously uninfected part of the country.
- Animals can move freely within a PZ, so any decision to extend a PZ geographically (e.g. to allow vaccination in a wider area) must be balanced against the risk of wider movement of potentially infected animals.
Surveillance Zone
- A Surveillance zone is established in order to maintain a buffer area around the Protection zone. This size of the zone is set in EU legislation at at least 150km radius from any infected premises.
- Due to the nature of the spread of Bluetongue, new cases can be found outside of the Protection Zone.
- Any movement of susceptible animals out of the Surveillance zone (although a lesser risk than the Protection zone) has the potential to spread disease to a new and previously uninfected part of the country.
- Therefore the zone, and the movement restrictions within provide a vital buffer against further, and wider spread of disease.
Moves to Slaughter
- Given the nature of the UK farming industry, there is an economic need to allow moves to slaughter, potentially long distances and moving out of zones.
- As infected animals (showing no symptoms) can potentially move to slaughter out of the restricted zones, there is potential for midges at the abattoir of destination to bite them and become infected. This can potentially lead to the creation of a local infection in a previously uninfected area.
- Therefore there is a need to mitigate against the risk of midges biting potentially infectious animals in abattoirs, through licence conditions. As such the following measures are required for moves to slaughter (outside the “vector free period”, VFP).
- A requirement for animals to arrive at abattoirs after dawn, and slaughter animals of the before dusk each day. This minimises the risk of potentially infectious animals being bitten at abattoirs during peak times of midge activity i.e. dawn and dusk.
- Similarly, potentially infectious animals should not be present in abattoirs overnight, as midges are still fairly active at night, and would be particularly attracted by lighting at the abattoirs (as opposed to during the day)
- Vehicles used to transport animals should be treated with authorised insecticides prior to the movement. This will reduce the likelihood of potentially infected midges entering the vehicles and moving with the animals out of the zones.
- Insecticide treatment of the animals to mitigate the same risk is not possible due to the withdrawal periods.
- During the period of low vector activity is has been possible to relax these time constraints and allow movements of livestock to slaughter from the restricted areas through dedicated slaughter markets.
Moves to Live
- Due to the nature of the disease, all animals in the Protection and Surveillance Zones must be considered as potentially infected (although there is a higher risk in the PZ).
- Therefore, any moves of animals outside of the Restricted Zones can potentially lead to the creation of a local infection in a previously uninfected area.
- In the current period of low vector activity moves to live are being allowed out of the current Restricted Zone, providing the livestock meets specific criteria and has a pre-movement test, but such moves will only be allowed after the VFP ends under very specific criteria (e.g. naturally immune animals). Moves out of zones to slaughter will however be allowed (see above).
Transiting zones
- All movements of animals from and to a lower risk area through a higher risk area provide a level of risk to the transiting animals of being bitten by potentially infected midges while in transit, and transferring infection to a previously uninfected area.
- Therefore conditions are required for such moves (outside the VFP) to mitigate against the risk of animals being bitten in transit.
- Moves from free area to free area through a SZ, are subject to the vehicle and animals being treated with insecticides prior to entering the SZ. No stops, apart from required rest periods or for welfare reasons are permitted.
Page last modified: 11 April, 2008